Automotive Mechanics Series Automotive F
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Behind William H. Crouse's clear technical writing is a background of sound mechanical engineering training as well as a variety of practical industrial experiences. He spent a year after finishing high school working in a tinplate mill, summers, while still in school, working in General Motors plants, and three years working in the Delco-Remy Division shops. Later he became Director of Field Education in the Delco-Remy Division of General Motors Corporation, which gave him an opportunity to develop and use his natural writing talent in the preparation of service bulletins and educational literature. During the war years, he wrote a number of technical manuals for the Armed Forces. After the war, he became Editor of Technical Education Books for the McGraw-Hill Book Company. He has contributed numerous articles to automotive and engineering magazines and has written several outstanding books:
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McGRAW-HILL
Automotive Mechanics Series
BY WILLIAM H. CROUSE
Automotive Engines
Automotive Fuel, Lubricating, and Cooling Systems
Automotive Chassis and Body
Automotive Power Trains and Transmissions
Automotive Electrical Equipment
OTHER BOOKS BY WILLIAM
H.
CROUSE
Automotive Mechanics
and five accompanying study guides:
WORKBOOK FOR AUTOMOTIVE CHASSIS
WORKBOOK FOR AUTOMOTIVE ELECTRICITY
WORKBOOK FOR AUTOMOTIVE ENGINES
WORKBOOK FOR AUTOMOTIVE SERVICE
AND TROUBLESHOOTING
WORKBOOK FOR AUTOMOTIVE TOOLS
Everyday Automobile Repairs
AUTOMOTIVE
~
Fuel, Lubricating
and
Cooling Systems
Construction, Operation, and Maintenance
'SECOND EDITION
--
William' H. Crouse
McGRAW-HILL BOOK COMPANY, INC.
New York
Chicago
San Francisco
Dallas
Toronto
London
ABOUT THE AUTHOR
Behind William H. Crouse's clear technical writing is a background of sound
mechanical engineering training as well as a variety of practical industrial experiences. He spent a year after finishing high school working in a tinplate
mill, summers, while still in school, working in General Motors plants, and
three years working in the Delco-Remy Division shops. Later he became Director of Field Education in the Delco-Remy Division of General Motors
Corporation, which gave him an opportunity to develop and use his natural
writing talent in the preparation of service bulletins and educational literature.
During the war years, he wrote a number of technical manuals for the
Armed Forces. After the war, he became Editor of Technical Education
Books for the McGraw-Hill Book Company. He has contributed numerous
articles to automotive and engineering magazines and has written several outstanding books: Automotive Mechanics, Electrical Appliance Serdcing, Everyday Automobile Repairs, Everyday Household Appliance Repairs, and Under-
standing Science.
William H. Crouse's outstanding work in the automotive field has earned
for him membership in the Society of Automotive Engineers and in the American Society for Engineering Education.
AUTOMOTIVE FUEL, LUBRICATING, AND COOLING SYSTEMS
Copyright © 1959 by the McGraw-Hill Book Company, Inc.
Copyright © 1955 by the McGraw-Hill Book Company, Inc. Printed in the
United States of America. All rights reserved. This book, or parts thereof, may not be reproduced in any form without permission of the publishers.
Library of Congress Catalog Card Number: 58-11979
v
How to study this book
THIS IS one of a series of five books covering in detail the construction, operation, and maintenance of automobiles. The five
books are designed to give you the complete background of information you need to become an automotive mechanic. Furthermore,
the comprehensive coverage of the subject matter in the books
should make them a valuable addition to the library of anyone
interested in any phase of automobile engineering, manufacturing,
sales, service, and operation.
GETTING PRACTICAL EXPERIENCE
Of course, these books alone will not make you an automotive
mechanic, just as books alone do not make an airplane pilot or a
dentist or an architect the expert he is. Practice also is required,
practice in handling automotive parts and automotive tools and in
following automotive servicing procedures. The books will give you
the theoretical background you need, but you should seek out means
of getting practice, also. If you are taking a regular course in automotive mechanics, you will get practical experience in the school
automotive shop. But if you are not taking a regular course in
a school, you may still be able to make use of the facilities of any
nearby school with an automotive shop. Perhaps you will meet
others who are taking an automotive mechanics course and can talk
over any problems you have. This often clears up difficult points. A
local garage or service station is a good source of practical information. If you can get acquainted with the automotive mechanics
there, so much the better. Watch them as they work; notice how
they do things. Then go home and think about it. Perhaps the
mechanics will allow you to handle various parts and possibly even
help with some of the servicing jobs.
[v]
How to Study This Book
SERVICE PUBLICATIONS
While you are in the service shop, try to get a chance to study
the various publications they receive. Automobile manufacturers, as
well as suppliers of parts, accessories, and tools, publish shop
manuals, service bulletins, and parts catalogues. All these are
designed to help service personnel do a better job. In addition,
numerous automotive magazines are published which deal with the
problems and methods of automotive service. All these publications
will be of great value to you; study them carefully.
These various activities will help you gain practical experience in
automotive mechanics. Sooner or later this experience, plus the
knowledge that you have gained in reading the five books in the
McGraw-Hill Automotive Mechanics Series, will permit you to step
into the automotive shop on a full-time basis. Or, if you are already
in the shop, you will be equipped to step up to a better and a more
responsible job.
CHECKING UP ON YOURSELF
Every few pages in the book you are given the chance to check
the progress you are making by answering a series of questions.
You will notice that there are two types of tests, progress quizzes
and chapter checkups. Each progress quiz should be taken just after
you have completed the pages preceding it. The quizzes allow you
to check yourself quickly as you finish a lesson. On the other hand,
the chapter checkups may cover several lessons, since they are
review tests of entire chapters. Since they are review tests, you
should review the entire chapter by rereading it or at least paging
through it to check important points before trying the test. If any
of the questions stump you, reread the pages in the book that will
give you the answer. This sort of review is very valuable and will
help you fix in your mind the essential information you will need
when you go into the automotive shop. Do not write in the book.
Instead, write down your answers in a notebook.
KEEPING A NOTEBOOK
Most of the questions require a written answer. It would be well
for you to keep a notebook and write the answers in the notebook. .
[vi}
How to Study This Book
Also, you can write down in the notebook important facts that you
pick up from reading the book or from working in the shop. As you
do this, you will find that the notebook will become a valuable
source of information to which you can refer. Use a loose-leaf, ringbinder type of notebook so that you can insert or remove pages and
thereby add to and improve your notebook.
GLOSSARY AND INDEX
There is a list of automotive terms in the back of the book, along
with their definitions. Whenever you have any doubt about the
meaning of some term or about what purpose some automotive part
has, you can refer to this list, or Glossary. Also, in the back of the
book you will find an Index. This Index will help you look up anything in the book that you are not sure about. For example, if you
wanted to refresh your mind on how some component works, you
could find it quickly by looking in the Index to find what pages the
information is on.
AUTOMOTIVE TOOLS AND COMPONENTS
In the Automotive Engines book (one of the five books in the
McGraw-Hill Automotive Mechanics Series) there is a chapter on
automotive tools. This chapter is an important one and should be
studied along with any of the books in the McGraw-Hill Automotive
Mechanics Series. In other words, the information in the chapter
on tools applies to all service operations on the car, and not just to
engine service. The Automotive Engines book also has a chapter on
automotive components that describes brieRy the operation of all
the mechanisms in the automobile. Reference should be made to
this chapter if the reader desires a short explanation of any
component.
And now, good luck to you. You are engaged in the study of a
fascinating, complex, and admirable mechanism-the automobile.
Your studies can lead you to success in the automotive field, a field
where opportunities are great. For it is the man who knows-the
man who can do things-who moves ahead. Let this man be you.
WILLIAM
H.
CROTJSE
[ vii]
Pl'eface to the·second edition
RAPID technological developments in the automotive field, as well
as advancements in educational methods required to keep pace with
these new developments, have made advisable a new edition of
Automotive Fuel, Lubricating, and Cooling Systems. This revision
includes material on the new automotive equipment introduced in
the past three years and related servicing techniques. Insofar as possible, this new material has not been appended to the old; instead,
it has been integrated into the pattern of the text so that the student
sees the new material as part of the complete presentation.
The comments and suggestions of teachers and. students who have
used the earlier edition have been carefully analyzed and acted upon
where possible during the revision of the text. Reports of their experience in the actual use of the text for classroom and home study
have been of paramount importance to the author in his efforts to
make the book of maximum usefulness. Improvements that have
been made in the present edition, therefore, should be credited to
these users, and acknowledgment of their helpful suggestions is
herewith gratefully extended.
WILLIAM
\
H.
CROUSE
Contents
v
viii
How to Study This Book .
Preface to the Second Edition
xv
Acknowledgments
1
1. AUTOMOTIVE FUNDAMENTALS
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11. Exhaust.
Purpose of This Book.
12. Piston Rings.
Components of the Automobile.
13. Multiple-cylinder Engines.
The Engine.
14. Engine Flywheel.
The Engine Cylinder.
Changing Reciprocating Motion to 15. Engine Classifications.
Rotary Motion.
16. Cylinder Arrangements.
The Valves.
17. Valve Arrangements.
Engine Operation.
18. Engine Accessory Systems.
Intake.
19. The Ignition System.
Compression.
20. Operation of Ignition-advance
Mechanisms.
Power.
28
2. FUEL·SYSTEM FUNDAMENTALS .
21.
22.
23.
24.
25.
26.
27.
28.
29.
Purpose of the Fuel System.
Components in the Fuel System.
Atoms and Elements.
Size of Atoms.
Atomic Structure.
Molecules.
Combustion.
Heat.
Change of State.
30. Expansion of Solids Due to Heat.
31. Expansion of Liquids and Gases
Due to Heat.
32. Increase of Pressure with
Temperature.
33. Gravity.
34. Atmospheric Pressure.
35. Vacuum.
41
3. FUEL-SYSTEM OPERATION
36.
37.
38.
39.
40.
Fuel Tan1e
Fuel Filters and Screens.
Fuel Gauge.
Fuel Pump.
Combination Fuel and Vacuum
Pumps.
41. Electric Fuel Pumps.
42. Air Cleaner.
43. Intake Manifold.
44.
45.
46.
47.
48.
49.
50.
51.
Carburetor.
Evaporation.
Atomization.
Carburetor Fundamentals.
Float BowL
Exhaust System.
Muffler.
Dual Exhaust System.
[ix]
Contents
67
4. CARBURETOR FUNDAMENTALS
52.
53.
54.
55.
56.
57.
58.
59.
60.
61.
62.
63.
64.
65.
Air-Fuel Ratio Requirements.
Carburetor Circuits.
Float Circuit.
Concentric Float Bowls.
Dual-float Circuits.
Float-bowl Vents.
Idling and Low-speed Circuits.
Low-speed Operation.
Other Idle and Low-speed Circuits.
High-speed, Part-load Circuit.
Multiple Venturi.
Other High-speed Circuits.
High-speed, Full-power Circuit.
Mechanically Operated Full-power
Circuit.
66. Vacuum-opcrated Full-power
Circnit.
67. Combination Mechanically
Operated and Vacuum-operated
Full-power Circuit.
68. Accelerator-pump Circuit.
69. Other Accelerator-pump Circuits.
70. Combination Accelerator Pump and
Full-power Valve.
71. Choke.
7'2. Automatic Chokes.
73. :\lanifold Heat Control.
74. V-8 Manifold Heat Control.
75. Anti-icing.
76. Throttle Cracker.
77. Fast Idle.
78. Antipercolator.
79. Air Bleed.
80. Compensating System.
107
S. AUTOMOTIVE CARBURETORS
81.
82.
83.
84.
85.
86.
Accessory Devices on Carburetors.
Ignition-distributor Controls.
Starting-control Switches.
Throttle-return Checks.
Governor.
Carburetor Assembly.
87. Updraft Carburetors.
88. Horizontal Air Entrance.
89. Dual Carhuretors.
90. Four-barrel Carburetor.
gl. Ford Carburetors.
92. Multiple-carburetor Installations.
6. FUEL-INJECTION and LPG FUEL SYSTEMS
93.
94.
95.
96.
Gasoline Fuel-injection System.
Ramjet Fuel-injection System.
Air Intake.
Fuel Intake.
7. AUTOMOTIVE-ENGINE
97. Diesel-engine Operation.
98. Diesel-en 6ine Fuel-injection System.
99. Liquefied Petroleum Gas Fuel
Systems.
159
FUELS
100. Automotive-engine Fuels.
101. Gasoline.
102. Origin of Gasoline.
103. Volatility.
104. Antiknock Value.
105. Compression Ratio.
106. Heat of Compression.
107. Cause of Knocking.
108. Meas\uing Antiknock Values of
Fuels...
[x]
145
109. Detonation versus Preignition.
110. Chemical Control of Knocking.
111. Factors Affecting Knocking.
112. Chemical versus Mechanical
Octane.
113. Octane Requirements.
114. Harmful Chemicals and Cum in
Gasoline.
115. Chemistry of Combustion.
116. Diesel-engine Fuels.
Contents
~
117.
118.
119.
120.
Viscosity.
Cetane Number.
Cetane-number Requirements.
Fuel-oil Purity.
121. Liquefied Petroleum Gas.
122. Types of LPG.
123. LPG Economy.
8. DIAGNOSING FUEL-SYSTEM TROUBLES
124.
125.
126.
127.
128.
129.
130.
131.
I32.
133.
134.
135.
How to Study This Chapter.
Need for Logical Procedure.
Testing Instruments.
Fuel-mileage Testers.
Exhaust-gas Analyzers.
Low-pressure Gauges for
Measuring Fuel-pump Pressure.
Fuel-pump Capacity Testers.
Fuel-pump Vacuum Tester.
Vacuum Gauges for Measuring
Intake-manifold Vacuum.
Tachometers.
Chassis l;)ynamometers.
Trouble Tracing in Fuel System.
9. FUEL-SYSTEM SERVICE
148.
149.
150.
151.
152.
153.
154.
155.
/ 156.
157.
158.
159.
Cleanliness.
Air-cleaner Service.
Manual-choke Adjustment.
Automatic-choke Adjustment.
Removing Hot-air Choke.
Servicing and Replacing Hot-air
Choke.
Fuel Tank.
Fuel Lines.
Fuel Gauges.
Fuel-pump Inspection.
Fuel-pump Troubles.
Fuel-pump Removal.
10. CARBURETOR SERVICE
166.
167.
168.
169.
170.
171.
172.
173.
174.
Cleanliness.
Carburetor Troubles.
Typical Carburetor Adjustments.
Idle-speed and Idle-mixture
Adjustments.
Float Level.
Accelerator Pump.
Metering Rod.
Antipercolator.
Throttle Linkage.
184
136. Fuel-system Trouble-shooting
Chart.
137. Excessive Fuel Consumption.
138. Engine Lacks Power, Acceleration,
or High-speed Performance.
139. Poor Idle.
140. Engine Will Not Start Except
When Primed.
141. Hard Starting with Engine Warm.
142. Slow Engine Warm-up.
143. Smoky, Black Exhaust.
144. Engine Stalls.
145. Engine Backfires.
146. Engine Runs but Misses.
147. Quick Carburetor Checks.
211
160. Fuel-pump Disassembly and
Assembly.
161. Fuel-pump Disassembly and
Reassembly, Type 1.
162. Fuel-pump Disassembly and
Reassembly, Type 2.
163. Combination Fuel- and
Vacuum-pump Disassembly and
Reassembly, Type 1.
164. Combination Fuel- and
Vacuum-pump Disassembly and
Reassembly, Type 2.
165. Fuel-pump Installation.
239
175. Carburetor Removal.
176. Carburetor Overhaul Procedures.
177. Overhauling Chevrolet
Carburetors.
178. Adjustments (Chevrolet Model in
Fig. 10-6).
179. Disassembly (Chevrolet Model in
Fig. 10-6).
180. Reassembly (Chevrolet Model in
Fig. 10-6).
[xi]
Contents
181. Overhauling Plymouth
Carburetors.
182. Adjustments (Plymouth).
183. Disassembly and Reassembly
( Plymouth) .
184. Overhauling Two-barrel
Carburetors.
185. Adjustments (Two-barrel
Carburetor) .
186. Disassembly.
187. Reassembly.
188. Overhauling Ford Carburetors.
189. Adjustments on Carburetors
Shown in Fig. 10-25.
190. Disassembly of Carburetor Shown
in Fig. 10-25.
191. Reassembly.
192. Adjustments on Carburetor Shown
in Fig. 10-31.
193. Disassembly of Carburetor Shown
in Fig. 10-31.
194. Reassembly of Carburetor.
195. Overhauling Four-barrel
Carburetors.
196. Adjustments (Four-barrel Unit).
197. Disassembly.
198. Carburetor Reassembly.
199. Carburetor Installation.
291
11. ENGINE LUBRICATING SYSTEMS
Friction.
Dry Friction.
Greasy Friction.
Viscous Friction.
Theory of Lubrication.
Types of Bearings.
Friction Bearings.
Friction-bearing Lubrication.
Antifriction Bearings.
Purpose of Engine Lubricatil\g
System.
210. Source of Oil.
211. Properties of Oil.
212. Water-sludge Formation.
200.
201.
202.
203.
204.
205.
206.
207.
208.
200.
213. Service Ratings of Lubricating
Oil.
214. Oil Changes.
215. Oil Consumption.
216. Automotive Lubricants.
_/' 217. Types of Lubricating Systems.
218. Oil Pumps.
219. Relief Valve.
220. Oil Filters.
221. Oil Coolers.
222. Oil-pressure Indicators.
/ 223. Crankcase Ventilation.
224. Oil-level Indicators.
12. LUBRICATING-SYSTEM SERVICE
225. Testing Instruments.
226. Lubricating-system Checks.
227. Trouble Tracing in Lubrication
System.
228. Lubricating-system Service.
229. Changing Oil.
230. Oil-pan Service.
. 885
231.
232.
233.
234.
235.
236.
Relief Valve.
Oil Filters.
Filter-element Replacement.
Oil Pumps.
Oil-pressure Indicators.
Cleaning Valves and Piston Rings.
854
13. ENGINE COOLING SYSTEM
" 237. Purpose of Engine Cooling
/
System.
,238. Air-cooled Engines.
239. Liquid-Cooled Engines.
240. Watei Jackets.
/241. Water \Pumps.
242. Engine
[xii]
\an.
·243.
244.
/,245.
/ 246.
I 247.
248.
Radiator.
Hot-water Car Heater.
Thermostat.
Radiator Pressure Cap.
Antifreeze Solutions.
Temperature Indicators.
Contents
.
14. COOLING-SYSTEM SERVICE
249.
250.
251.
252.
Cooling-system Tests.
Care of Cooling System.
Trouble Diagnosis.
Cleaning the Cooling System.
376
253. Locating and Repairing Radiator
Leaks.
254. Water-pump Service.
Appendix A: Exhaust-gas Analyzers .
399
Appendix S: Glossary .
402
Index
..
419
Acknowledgments
DURING the several years that the five books in the McGraw-Hill Automotive Mechanics Series (of which this is one) were in preparation,
the author was given invaluable aid and inspiration by many, many
people in the automotive industry and in the field of education. The author gratefully acknowledges his indebtedness and offers his sincere
thanks to these many people. All cooperated with the aim of providing
accurate and complete information that would be useful in the training
of automotive mechanics. Special thanks are due to the following organizations for information and illustrations that they supplied: AC
Spark Plug Division, Buick Motor Division, Cadillac Motor Car Division,
Chevrolet Motor Division, Delco Products Division, Delco-Remy Division, Detroit Diesel Engine Division, Frigidaire Division, Oldsmobile
Division, Pontiac Motor Division, Saginaw Steering Gear Division, and
United Motors Service Division of General Motors Corporation; Allen
Electric and Equipment Company; American Exporter's Automotive
World; Akron Equipment Company; American Motors Corporation;
Barrett Equipment Company; Bear Manufacturing Company; Bendix
Products Division of Bendix Aviation Corporation; Black and Decker
Manufacturing Company; Carter Carburetor Company; Chrysler Sales
Division, De Soto Division, Dodge Division, and Plymouth Division of
Chrysler Corporation; Clayton Manufacturing Company; Henry Disston
and Sons, Inc.; Eaton Manufacturing Company; E. 1. du Pont de Nemours & Company, Inc.; Electric Auto-Lite Company; Federal-Mogul
Corporation; E. Edelmann and Company; Federal Motor Truck Company; Ford Motor Company; Gemmer Manufacturing Company; B. F.
Goodrich Company; Greenfield Tap and Die Corporation; Hall Manufacturing Company; Jam Handy Organization, Inc.; Hercules Motors
Corporation; Hobart Brothers; Hotpoint, Inc.; Houde Engineering Division of Houdaille-Hershey Corporation; International Harvester Company; Kaiser Motors Corporation; K-D Manufacturing Company; KelseyHayes Wheel Company; Kent-Moor Organization, Inc.; Johnson Bronze
Company; King-Seeley Corporation; Lincoln-Mercury Division of Ford
Motor Company; Linde Air Products Company; Mack-International
{xv]
Acknowledgments
Motor Truck Corporation; Metalizing Company of America; Alexander
Milburn Company; Monmouth Products Company; Monroe Auto Equipment Company; Muskegon Piston Ring Company; New Britain Machine
Company; North American Electric Lamp Company; Perfect Circle
Company; Ramsey Accessories Manufacturing Company; Rottler Boring
Bar Company; A. Schrader's Son Division of Scovill Manufacturing Company, Inc.; Sealed Power Corporation; South Bend Lathe Works; Spicer
Manufacturing Corporation; Standard Oil Company; Storm Manufacturing Company, Inc.; Studebaker-Packard Corporation; Sun Electric
Corporation; Sunnen Products Company; Thompson Products Inc.;
United Specialties Company; United States Rubber Company; Van
Norman Company; Warner Electric Brake Manufacturing Company;
Waukesha Motor Company; Weaver Manufacturing Company; Wilkening Manufacturing Company; and Zenith Carburetor Company.
Special thanks are also due to the staff and instructors at General
Motors Institute; they supplied the author with much excellent information and gave him great assistance during certain phases of the work on
the McGraw-Hill Automotive Mechanics Series. To all these organizations and the people who represent them, sincere thanks!
WILLIAM
H.
CROUSE
I: Automotive fundamentals
THIS CHAPTER discusses engine operation. It supplies you with
the background information you need to understand the operation
of the fuel, lubricating, and cooling systems.
§1. Purpose
You have shown your interest in automotive engines by starting to read this book. We hope to maintain
your interest by giving you, in the pages of this book, a great deal
of information on engine fuel, cooling, and lubricating systems.
Another book in the McGraw-Hill Automotive Mechanics Series
(Automotive Engines) describes in detail engine construction,
operation, and service. This book covers the fuel, cooling, and
lubricating systems used on automotive engines and supplies details of their construction, operation, and service. Regardless of
what job you have or hope to have in the future in the automotive
field, the information in this book should prove of value to you.
The automotive mechanic, the automotive engineer, the man working at the higher level in automotive manufacture, sales, service,
or operation should be able to do his job better if he has the information in this book at his finger tips. And naturally, this information will equip him for the bigger job ahead. The man who
knows the facts and can use them in a practical way is the man
who forges ahead in his chosen field. This book is designed to help
you be that man.
of this book
§2. Components of the automobile Before we begin our studies of
the fuel, lubricating, and cooling systems, let us first take a quick
look at the complete automobile and the automobile engine. The
automobile might be said to consist of five basic mechanisms, or
components. These are:
1. The engine, which is the source of power and which includes
the fuel, lubricating, cooling, and electric systems.
[1]
FIG. 1-1. Chassis of a passenger car. (Metcury Division of Ford Motor
Company)
FIG. 1-2. A typical ~ix-c
: ' lind
er
engine partly cut away to show the internal construction. (Ford DiVision of Ford Motor Company)
\
§3
Aut()'l1{otive Fundamentals
2. The frame, which supports the engine, wheels, steering and
braking systems, and body.
3. The power train, which carries the power from the engine
(through the clutch, transmission, propeller shaft, differential,
and axles) to the car wheels.
4. The car body.
5. Car-body accessories, including heater, lights, windshield
wipers, and so forth.
Figure 1-1 illustrates the chassis of an automobile. The chassis
is made up of the frame, engine, power train, wheels, and steering
and braking systems.
§3. The engine The engine (Fig. 1-2) is the source of power that
makes the wheels turn and the car move. It is usually called an
internal-combustion engine because gasoline is burned inside the
FIG. 1-3. Cutaway view of an eight-cylinder V-type engine. (Mercury Division
of Ford Motor Company)
engine (in the engine cylinders or combustion chambers). This is
in contrast to external-combustion engines (such as steam engines)
where the combustion takes place outside the engine. It is the
burning of the gasoline in the engine cylinders that produces the
[3]
\
§4
Automotive Fuel, Lubricating, and Cooling Systems
power. The power is carried from the engine through the power
train to the car wheels so that the wheels turn and the car moves.
The fuel system plays a vital part in the power-producing process,
since it supplies the gasoline to the engine cylinders. Before we
describe how the fuel system does its job, let us first review the
FIG. 1-4. Cross-sectional view of a six-cylinder engine. Piston is at top of
stroke. Both piston and cylinder are shown cut in half. (Chev1'01et Motor Division of General Motors Corporation)
actions that go on in the engine cylinders. Most automotive engines
have six or eight cylinders. Since the same actions go on in each
cylinder, we need to examine only one cylinder of the engine.
§4. The
Figure 1-3 shows an engine cylinder, cut
away so tha~
the internal parts can be seen. This is the end
cylinder of ,a ' six-cylinder engine; the other five cylinders are not
shown. Fig~
1-4 shows a cutaway view of a similar engine. These
two pictures '!\lay be somewhat confusing since they show so many
[4]
\.
engine cylinder
§4
Automotive Fundamentals
parts, so let's simplify the cylinder by showing it as nothing more
than a round container, closed at one end and open at the other
(Fig. 1-5), like a tin can with the bottom cut out. A movable piston
fits into the cylinder. The piston is slightly smaller in size (or
diameter) than the cylinder, so that it can slip up into the cylinder
as shown in Fig. 1-5 (at b). Note that the cylinder is drawn as
a
b
FIG. 1-5. Three steps in the actions in an engine cylinder. (a) The piston is
a second cylinder that fits snugly into the engine cylinder. (b) When the piston
is pushed up into the engine cylinder, air is trapped and compressed. The
cylinder is drawn as though it were transparent so the piston can be seen.
(c) As the pressure increases due to the burning of the gasoline vapor, the
piston is pushed out of the cylinder.
can
though it were transparent so that the actions in the cylind~r
be seen. For the moment, you can think of the piston as a solid
plug which can be slid up into the cylinder. This action traps air
in the cylinder and compresses it (Fig. 1-5b). If we could put
some gasoline vapor in with the compressed air, and then apply a
lighted match or an electric spark to the air-vapor mixture, it is
obvious what would happen. There would be an "explosion" that
would blow the piston out of the cylinder as shown in Fig. 1-5c.
[5]
Automotive Fuel, Lubricating, and Cooling Systems
§5
This is actually what happens (with some modification) in each
engine cylinder. A mixture of gasoline vapor and' air enters the
cylinder, the piston pushes up into the cylinder to compress the
mixture, and then an elecb'ic spark ignites the compressed mixtu,re
fiston pin)
o
Cronksllaft
Rod beoring
cop~
Crankshaft
~
FIG. 1-6. A piston, connecting rod,
piston pin, and crankpin on engine
crankshaft in disassembled view.
FIG. 1-7. Piston and connecting-rod
assem bly attached to crankpin on
crankshaft. Piston is shown partly cut
away so you can see how it is attached to connecting rod.
so that the piston is forced downward. Of course, in the engine the
piston is not blown clear out of the cylinder; the piston simply
moves up and down in the cylinder-up to compress the mixture,
down as the mixture burns.
§5. Changing reciprocating motion to rotary motion The piston
moves up and down in the cylinder. This straight-line motion is
called reCiprocating motion; the piston moves in a straight line.
This straight-line motion must be changed to rotary motion before
it can be sed to make the car wheels rotate. A connecting rod and
[6)
~6
Automotive Fundamentals
a crank on the engine crankshaft make this change (Fig. 1-6). The
crank is an offset section of the crankshaft. It swings arolmd in a
circle as the shaft rotates. The connecting rod connects between
the crankpin on the crank and the piston (Fig. 1-7). The crank
end of the connecting rod is attached to the crankpin by fastening
the rod cap to the connecting rod with the rod bolts. Bearings in
the rod and cap permit the crankpin to rotate freely within the
rod. The piston end of the connecting rod is attached to the piston
2
i
+
4
+
Pisto n
Connecting rod
5
6
t
7
t
t
1-8. Sequence of actions as crankshaft completes one revolution and as
piston moves from top to bottom to top again.
FIG.
by the piston pin (or wrist pin). Bearings in the piston, or in the
rod permit the rod to tilt back and forth freely.
Now, let us see what happens as the piston moves up and down
in the cylinder (Fig. 1-8). As the piston starts down, the connecting
rod tilts to one side so that the lower end of the rod can follow the
circular path of the crankpin. Study the sequence of action in Fig.
1-8 to see how the rod tilts first to one side and then to the other as
the lower end moves in a circle with the crankpin.
§6. The valves There must be some means of getting the burned
gasoline vapor out of the engine cylinder, and also of getting fresh
charges of gasoline vapor and air into the cylinders. The engine
[7J
§6
Automotive Fuel, Lubricating, and Cooling Systems
valves do this job. There are two openings, or ports, in the enclosed
end of the cylinder. One of these is shown in Fig. 1-3. There is a
valve in each port. The valves are accurately machined plugs on
long stems. When they are closed or seated (that is, moved down
into the ports), the ports are sealed off and gas cannot pass through
the ports. When the valve is opened (as shown in Fig. 1-9) , gas
can pass through the port.
Valve guide
Yolve spring
Valve -lifter
tension spring -;;;---;4"1,
\{live I ifler
FIG. 1-9. A valve and valve seat in
cylinder.
1-10. Valve mechanism. Valve is
raised off seat With every camshaft rotation. (Studebaker-Packard Corpomtion)
FIG.
The valves are opened by cams on the engine camshaft. A cam
on the camshaft, as well as the rest of the valve-operating mechanism, is shown in Fig. 1-10. The cam has a high point, or lobe;
every time the cam rotates, the lobe comes around under the valve
lifter an.d ,moves it upward. The lifter then carries this upward
move~
to the valve stem, causing the valve to move up, or open. ·
Then, aft~
the cam has turned enough to move the lobe out from
under the ilifter, the heavy valve spring pulls the valve back on its
[81
\,
Automotive Fundamentals
§8
seat. The spring is attached to the lower end of the valve stem by
a spring retainer and lock.
There is a cam for each valve (two cams per cylinder) on the
engine camshaft. The camshaft is driven off the crankshaft by gears
or by sprockets and a chain.
§7. Engine operation We have noted that the piston moves up and
down in the cylinder and that the valves open and close to admit
fresh charges of air and gasoline vapor and also to discharge burned
gases. Let us see how these actions occur. The actions can be
divided into four stages, or into four piston strokes. "Stroke" refers
to the piston movement. A stroke occurs when the piston moves
from one limiting position to the other. The upper limit of piston
movement is called top dead center, or TDC. The lower limit of
piston movement is called bottom dead center, or BDC. A stroke
is piston movement from TDC to BDC, or from BDC to TDC.
When the entire cycle of events requires four piston strokes (two
crankshaft revolutions), the engine is called a four-stroke-cycle
engine, or a four-cycle engine. The four strokes are intake, comt. pression, power and exhaust. (Two-cycle engines are also in use;
in these, the entire cycle of events takes place in two strokes, or in
one crankshaft revolution.)
NOTE: For the sake of simplicity in the following discussion, the
valves are considered to open at TDC and BDC, that is, at the
upper and lower limits of piston movement. Actually, they do not.
The valves open well before the piston reaches BDC. Also, the
illustrations of the four strokes (Figs. 1-11 to 1-14) are much
simplified and show the intake and exhaust valves separated and
placed on either side of the cylinder. This is done so that both
can be shown in the same illustration.
§8. Intake (Fig. 1-11) On the intake stroke, the intake valve has
opened. The piston is moving down (being pulled down by the
rotation of the crankshaft). This piston movement creates a partial
vacuum in the cylinder. In a later chapter in the book we will go
into this matter in more detail. For the present, let us merely say
that air rushes into the cylinder past the intake valve to "fill up"
this vacuum. As the air moves toward the cylinder, it must pass
through the fuel-system carburetor. There it is charged with gasoline
[91
§9
Automotive Fuel, Lubricating, and Cooling Systems
vapor. Thus, it is a mixture of air and gasoline vapor that rushes
into the cylinder as the piston moves down on the intake stroke.
§9. Compression (Fig. 1-12) After the piston moves down to BDC
on the intake stroke, the intake valve closes. The lobe on the cam
controlling the intake valve has moved out from under the valve
lifter. Since the other valve is also closed, the upper end of the
cylinder is sealed. Now, as the piston moves up (pushed up by the
rotating crankshaft ), the mixture of air and gasoline vapor that has
,,
\
\
I
I
1-11. Intake stroke. The intake
valve (to left) has opened, and the
piston is moving downward, drawing
air and gasoline vapor into the
cylinder.
FIG .
FIG. 1-12. Compression stroke. The
intake valve has closed, and the
piston is moving upward, compressing the mixture.
been drawn into the cylinder is compressed. By the time the piston
has moved up to TDC, the mixture will have been compressed to a
seventh or an eighth of its original volume. That is like taking a
gallon of air and compressing it to a pint. This results in a fairly
high pressure in the cylinder.
§10. Power (Fig. 1-13) About the time the piston reaches T DC
on the com ression stroke, an electric spark occurs at the cylinder
spark plug. The spark plug is essentially two heavy wire electrodes;
(101
Automotive Fundamentals
§11
the spark jumps between these electrodes. The spark is produced
by the ignition system (discussed on a later page). It ignites, or
sets fire to, the compressed air-gasoline-vapor mixture. Rapid combustion takes place; high temperatures and pressures result. At
this instant, the resulting pressure on the top of the piston, pushing
it down, may amount to as much as two tons ( on a piston 3 inches
in diameter ). This powerful push forces the piston down, and a
power impulse is u·ansmitted to the crankshaft through the connecting rod and crank.
FIG. 1-13. Power stroke. The ignition
FIG. 1-14. Exhaust stroke. The ex-
system produces a spark that ignites
the mixture. As it burns, high pressure is created which pushes the
piston downward.
haust valve (to right) has opened,
and the piston is moving upward,
forcing the burned gases from the
cylinder.
§1 1.
Exhaust (Fig. 1-14 )
The piston is forced down by the pressure of the burning gasoline vapor during the power stroke. When
the piston reaches BDC, the exhaust valve opens. Now, as the
piston starts back up again (pushed up by the rotating crankshaft) ,
it forces the burned gases from the cylinder. By the time the piston
has reached TDC, the cylinder is cleared of the burned gases. The
exhaust valve closes and the intake valve opens. Then, the piston
starts back down again on the next intake stroke. The four cycles,
[11]
Automotive Fuel, Lub1'icating, and Cooling Systems
§12
or piston strokes, are continously repeated all the time that the
engine is running.
§12. Piston rings You can appreciate the fact that a great deal
of pressure exists above the piston during the compression and
RING DIAMETER
RADIAL THICKNESS
DIAMfTRAL TENSION
~
~:
TANGENTIAL TENSION
WIDTH
v=ENDS
e-:=::L
-! I- RING
/
}
/j15~-
SIDE CLEARANCE
GROOVE CLEARANCE
GAP
GROOVE DIAMETER
CHANNel
FIG. 1-15. A compression ring
(top) and an oil-control ring
(bottom ), with various parts
named. (Sealed Power Corporation)
FIG. 1-16. External and sectional views of piston with four
piston rings in place. The
upper two, 1 and 2, are top
and second compression rings.
The lower two, 3, are oilcontrol rings. (Plymouth Division of Chrysler Corporation)
power strokes. To prevent the escape of much of this pressure past
the piston (between the piston and cylinder wall) the piston
must be equipped with rings. The reason is this: the piston cannot be machined accurately enough to provide a sealing fit with
the cylinder wall. If it did make a gas tight fit, then it would be too
[~21
\.
\
•
Automotive Fundamentals
§13
tight to slip up and down easily. Furthermore, changes in dimensions due to temperature changes might make it stick tight;
this would mean that something might break (rod, piston, crankshaft). The metal of the piston expands with temperature increase;
if the piston fit properly when cold, it would stick when hot. To
provide a good seal that will expand and contract with changing
temperatures (and also to compensate for cylinder-wall wear),
piston rings are used.
Typical piston rings are shown in Fig. 1-15. The rings are of cast
iron or similar metal. They have a joint which permits them to be
expanded and slipped over the end of the piston. There are grooves
in the piston into which the rings are installed (Fig. 1-16). Actually,
only the upper two rings shown in Fig. 1-16 have the job of sealing
in compression and combustion pressure. These rings, called the
compression rings, do this by pressing tightly against the cylinder
wall and also against the side of the ring groove in the piston. The
lower two rings shown in Fig. 1-16 are oil-control rings. Their job
is to scrape excessive amounts of lubricating oil off the cylinder
walls. As we will mention again when we describe lubricating
systems, considerable amounts of lubricating oil are thrown on
the cylinder walls to provide for lubrication of the moving rings
and piston. In fact, there is so much oil that if most of it were not
removed, it would work up into the combustion chamber and burn,
producing carbon that would interfere with valve and spark-plug
action so that engine performance would be very poor. The oilcontrol rings scrape off most of this oil from the cylinder walls
and return it to the oil reservoir (oil pan) at the bottom of the
engine.
§13. Multiple-cylinder engines You will remember that the cylinder
produces only one power impulse every four piston strokes. During
exhaust, intake, and compression, the crankshaft is driving the
piston, forcing it to push out the burned gases, to draw in a fresh
charge, and to compress the charge. Thus, a one-cylinder engine
would give power only one-fourth of the time and would not be
smooth or powerful enough for automotive operation. To prOVide
for a more continuous flow of power, modern automotive engines
use four, six or eight cylinders. With a four-cylinder engine, the
power impulses would follow one another so that there would be
[13]
§1 4
Automotive Fuel, Lubricating, and Cooling Systems
a power impulse going on all the time. With the six-cylinder engine,
the power impulses would overlap to some extent while the eightcylinder engine would have two power impulses going on at all
times. This would give a relatively even flow of power.
§14. Engine flywheel Even though the power impulses of a multicylinder engine follow each other or overlap, additional smoothing
out of the power impulses is desirable. The engine flywheel does
this job and thus improves the smoothness of the engine. Figure 117 shows an engine crankshaft with the flywheel attached to one
end. The flywheel is a relatively heavy metal wheel. It resists any
sudden change of crankshaft (or engine) speed. Thus, when a
power impulse starts (with its initial high pressure), the crankshaft is given a momentary hard push (through the connecting rod
and crankpin). But the flywheel resists the tendency for the crankshaft to surge ahead. Thus, the momentary power peaks are leveled
off so that the engine runs smoothly.
The flywheel also serves as part of the engine clutch (on engines
so equipped). In addition, the flywheel has teeth on its outer
edge; the electric cranking-motor pinion teeth mesh with these
teeth when the engine is being cranked for starting.
§15. Engine classifications Engines can be classmed in several ways.
They cla n be classified by the type of fuel they use [gasoline, LPG
(liquefred petroleum gas), or diesel fuel oil]. Most of this book
pertai~s
to the gasoline fuel engine since most automotive engines
use gaspline as fuel. Later chapters describe LPG and diesel fuel
[14]
\.
(a)
(b)
FIG. 1-18. (a) Side sectional view and (b) end sectional view of a V-8 engine.
This is called a Fire Dome engine by the manufacturer; the combustion chambers are hemispherical in shape. Note valve and push-rod arrangement. (De
Soto Division of Chrysler Corporation)
[15]
Automotive Fuel, Lubt'icating, and Cooling Systems
§16
systems and the fuels these systems use. Engines can also be
classified as liquid-cooled or air-cooled, and this distinction is discussed in the chapters on engine cooling systems. Other ways of
classifying engines are by number and arrangement of cylinders,
and by arrangement of valves. These are discussed in the following
sections.
L-Head
F-Head
FIG.
§16.
T-Head
I-Head
V-Type I-Head
1-19. Valve arrangements for various engines.
Most automotive engines have four,
six, or eight cylinders. All cylinders are similar in construction and
in operation. Four-cylinder and Six-cylinder engines are in-line
engines; that is, the cylinders are arranged in a Single row (Fig.
1-2). Eight-cylinder engines may be in-line (all cylinders in a single
row) or V-8. In the V-8, the cylinders are arranged in two rows,
or banks, which are usually perpendicular (or 90 degrees) to each
other, (Fig. 1-18).
Cylinder arrangements
\
§1t , Valve
The valves may be in the block as shown
in Figs. 1-2 to 1-4, or they may be in the cylinder head, above the
cylin~er,
as shown in Fig. 1-18. An engine that has the valves in the
[16] .
arrangements
Automotive Fundamentals
§17
block is called an L-head engine because the cylinder and combustion chamber are in the shape of an inverted "L." An engine that
has the valves in the head is called an I -head engine (or overheadvalve engine) because the cylinder and combustion chamber are
in the shape of an "1." There is a type of engine that has valves in
Valve
(a)
FIG. 1-20. Valve-operating mechanism for an I-head, or overhead-valve, engine.
Sectional view of an actual engine is shown in (a). In (b) only the essential
parts are shown, including the gears to drive the camshaft from the crankshaft,
the valve lifters, push rods, rocker arms, and valves for one cylinder. (Buick
Motor Division of General Motors C~rpoatin)
both the block and the head; it is called an F -head engine. Comparison of different types of valve and cylinder arrangement is
shown in Fig. 1-19.
Figure 1-10 shows the valve mechanism in an L-head engine.
Figure 1-20 shows the valve mechanism for an overhead-valve (or
I-head) engine. Note that a rocker arm and push rod are needed for
[17]
Automotive Fuel, Lubricating, and Cooling Systems
§18
each valve in order to push down on the valve stem and thus open
the valve. In the L-head engine the valve lifter pushes up on the
valve stem.
§18. Engine accessory system The engine requires four accessory
systems to supply it with fuel and electric sparks, to cool it, and
to lubricate it. The fuel, lubricating, and cooling systems are considered in detail in later pages in the book. The system that provides the electric sparks (the ignition system) is discussed in detail
in Automotive Electrical Equipment (another book in the McGrawHill Automotive Mechanics Series). A brief discussion of the ignition
system follows.
§19. The ignition system The ignition system is part of the automotive electric system (Fig. 1-21). The electric system has several
jobs to do. It cranks the engine for starting, supplies the electric
sparks to ignite the compressed charges in the cylinders, operates
the radio and car heater, supplies light for night driving, and
operates gauges on the car dash that indicate battery charging rate,
oil pressure, engine temperature, and level of fuel in the fuel tank.
Figure 1-22 shows, in schematic view, a typical ignition system.
It consists of the source of electric power (the battery), ignition
switch, ignition coil, ignition distributor, spark plugs, and wiring.
The ignition has two jobs. First, it takes the low voltage from the
battery (or generator) and steps it up to the several thousand volts
needed to produce the sparks at the cylinder spark plugs. Secondly,
it delivers each spark to the proper cylinder at the proper instant.
The voltage step-up job is done by the ignition coil and the
distributor contact points. The contact points are mounted on a
plate inside the distributor housing. One of the paints is stationary;
the other is mounted on a movable arm. This arm is moved by a
breaker cam inside the housing. The breaker cam revolves (it is
driven by a gear from the engine camshaft), and as it does so,
lobes on the cam cause the movable contact-point arm to move,
closing and opening the contact pOints. When the contact paints
are closed (and ignition switch is on), electric current flows from
the battery through the ignition coiL Then, a moment later, as the
cam turns,further, a lobe on the cam moves the arm and separates
the contact points. The current stops flowing. During the time that
current :ijows,
the ignition coil becomes "loaded" with electric
,\
(18J
\
\
Automotive Fundamentals
§19
energy. Then, when the contact pOints separate and the current
stops flowing, the electric energy is released from the coil in the
form of a high-voltage surge.
NOTE: An ignition capacitor, or condenser, is connected across
CURRENT Eo VOLTAGE
REGULATOR
FIG. 1-21. A typical one-wire automobile electric system. Return circuits
between electric units are formed by the engine block and the car frame.
The symbol -1 means ground, or return circuit. (United Motors Service
Division of General Motors Corporation)
the contact pOints to prevent the high-voltage surge from discharging across the contact points. This saves the surge for its designed
purpose, which is to produce a spark at a spark-plug gap.
The high-voltage surge produced by the coil is carried by wires
to the distributor cap and from there to the spark plug of the
[19]
Autorrwtive Fuel, Lubricating, arul Cooling Systems
§20
cylinder that is ready to fire (air-fuel mixture compressed). The
surge passes through the center terminal of the distributor cap.
The center terminal is connected by a wire to the coil. The center
terminal is connected inside the cap by a contact spring to the
distributor rotor. The rotor is mounted on the breaker cam so that
it turns with the cam. As it turns, it connects between the center
Battery
Ignifion coil
FIG. 1-22. Typical ignition system. It consists of the battery (source of power),
ignition switch, ignition coil, distributor (shown in top view with cap removed
and placed above it), spark plugs, and wiring. Units are not in proportion.
(Delco-Remy Division of General Motors Corporation)
terminal and each outer terminal in turn. The outer terminals are
connected by wires to the spark plugs in the engine cylinders. Thus,
as each high-voltage surge is produced, it is led through the cap,
rotor, and wiring to the spark plug of the cylinder that is ready
to fire (piston nearing TDC on the compression stroke).
§20. Operati,on of ignition-advance mechanisms When the engine
is idling, the sparks are timed to appear in the engine cylinders
[20]
\
\
§20
Aut9ffl-otive Fundamentals
on their compression strokes.
just before the pistons reach T~C
But at higher speeds, the air-fuel mixture has less time to ignite
and bum. If ignition still took place just before TDC on the compression stroke, the piston would be up over the top and moving
WEIGHT
SPRING
~
~
~
HOUSING
DRive
SHAFT---I
O ___ WASHER
COUPLING PIN"\
o
I
5
3
I
I
I
I
I
6
I
I
=
7
i
I
O_SHIM
8
I
I
FIG. 1-23. Disassembled view of a distributor. Advance mechanism is to left.
(Delco-Remy Division of General Motors Corporation)
down before the mixture was well ignited. This means that the
piston would be moving away from the pressure rise; much of the
energy in the burning fuel would be wasted. However, if the
mixture is ignited earlier in the compression stroke (at high engine
[21]
Automotive Fuel, Lubricating, and Cooling Systems
§20
speed), the mixture will be well ignited by the time the piston
reaches TDC. Pressure will go up and more of the fuel energy will
be used.
1. Advance based on speed. To ignite the mixture earlier at high
speed, a spark-advance mechanism is used. This mechanism is incorporated in the ignition distributor. One type consists of a
centrifugal device that pushes the breaker cam ahead of the distributor shaft as engine speed increases. Figure 1-23 shows the parts
of this mechanism. The breaker cam is attached to an oval-shaped
advance cam and this assembly sets down on a plate attached to
the drive shaft. Two crescent-shaped advance weights are also
NO
ADVANCE
FUll ADVANCE
1
I
I
FIG. 1-24. Centrifugal-advance mechanism showing initiaI- and maximum-
advance positions. (Delco-Remy Division of General Motors Corporation)
assembled on the plate as shown in Fig. 1-24. Figure 1-24 also
shows how the mechanism operates to move the breaker cam ahead
as engine speed increases. With increasing engine speed the
advance weights move out against the weight-spring tension. This
movement pushes the breaker cam ahead so that the cam lobes
close and open the contacts earlier. The sparks thus occur earlier;
the spark is advanced so that ignition occurs earlier in the compression stroke.
Different engines require different amounts of spark advance at
various speeds. Typical advance curves are shown in Fig. 1-25. In
curve A, the spark is timed to occur just a few degrees of crankshaft rotation before TDC during idle. Then, as engine speed is
increased, tlle spark moves ahead, or advances, until it reaches a
maximum of 28 degrees at 2,900 rpm (revolutions per minute) .
\
[22]
\
'.
\
§20
Automotive Fundamentals
Curve B is a little more complicated. It "dog-legs," or changes
slope, at 1,500 rpm. A curve is worked out for each engine so that
the advance at any particular speed will provide best performance.
The mechanism is then built to provide this advance.
Figure 1-26 illustrates a distributor that achieves spark advance
with increasing speed by a different method. In this unit the contacts are mounted on a movable breaker plate. The plate is linked
to an airtight diaphragm. Movement of the diaphragm will cause
Maximum
advance
Engine rpm
FIG. 1-25. Typical centrifugal-advance curves.
the plate to rotate a few degrees and carry the contacts around
with it. This movement causes the contacts to be closed and
opened earlier so that a spark advance is produced. The plate
rotation results from the vacuum-line connection between the airtight diaphragm on the distributor and an opening in the carburetor
venturi. As we will explain later, vacuum increases in the carburetor venturi with increasing engine speed (§47). The greater
the vacuum (or the greater the engine speed), the further the
diaphragm is moved and the more the plate mOves to advance the
spark.
2. Advance based on intake-manifold vacuum. With a partly
closed throttle valve, there is a partial vacuum in the intake mani[23]
Automotive Fuel, Lubrlcating, and Cooling Systems
§20
[24]
\.
Automotive Fundamentals
§20
fold. Less air-fuel mixture gets into the engine cylinders and it is
therefore less highly compressed. This means the mixture burns
more slowly. An additional spark advance, under these conditions,
will allow the mixture ample time to burn and give up its energy
to the piston. Spark advance based on intake manifold vacuum is
achieved by an airtight diaphragm linked to a movable breaker
plate. This type of arrangement is shown in Fig. 1-26. A vacuum
connection is made to an opening just above the edge of the throttle
plate (B in Fig. 1-26) in the carburetor. Whenever the throttle is
opened, its edge moves past the opening, thus introducing the intake
manifold into the tube. This vacuum then causes diaphragm and
breaker plate movement. The spark is advanced. Note that advance
is based, in this arrangement, on manifold vacuum, which is
part-throttle vacuum. When the throttle is opened wide, there is
no appreciable manifold vacuum and thus there will be no vacuum
advance from this effect.
CHAPTER CHECKUP
NOTE: Since the following is a chapter review test, you should review
the chapter before taking the test.
Now that you have completed a chapter in the book, you will want to
test your knowledge of the subjects covered in the book. The questions
that follow have two purposes. One is to test your knowledge. The second
purpose is to help you review the chapter. The chances are that you will
not be able to answer, offhand, all the questions. If this happens, turn
back into the chapter and reread the pages that will give you the answer.
Don't be discouraged if you can't answer all the questions. Most good
students reread their lessons several times in order to be sure that the
essential information will "stick" with them. Rereading the pages and rechecking the questions will help you learn how to pick out and remember
the important facts in the book. And it is these important facts that will
help you when you go into the automotive shop, office, or laboratory.
Correcting Parts Lists
The purpose of this exercise is to give you practice in spotting unrelated parts in a list. For example, in the list, cylinder, piston, rings, whee'.
flywheel, crankshaft, you can see that wheel does not belong because it
is the only part named that does not belong in an engine.
In each of the lists, you will find one item that does not belong. Write
down each list in your notebook, but do not write down the item that
does not belong.
[25]
Automotive Fuel, Lubricating, and Cooling Systems
1. The four piston strokes are intake, compression, injection, power,
exhaust
2. The engine parts that change the reciprocating motion of the piston
to rotary motion include the connecting rod, crank on crankshaft,
cam on camshaft
3. The valve mechanism in the L-head engine includes the camshaft,
valve spring, crankshaft, valve, spring retainer, lock
4. The two types of piston rings are oil-control rings, compression rings,
performance rings
5. The ignition system includes the ignition coil, ignition distributor,
ignition switch, spark plugs, cranking motor, wiring
Completing the Sentences
The sentences below are incomplete. After each sentence thcre are several words or phrases, only one of which will correctly complete the sentence. \Vrite each sentence down in your notebook, selecting the proper
word or phrase to complete it correctly.
1. The connecting rod is attached to the piston by the rod cap
piston pin
cap bolts
cap bearing
2. The connecting rod is attached to the crankpin on the crankshaft by
the
piston pin
crank
rod cap
rod boots
3. In the standard engine each cylinder has
one valve
two
valves
three valves
four valves
4. The two types of engine valves are
intake and port
intake
and inlet
intake and exhaust
5. The four strokes in the engine are, in order of occurrence,
intake, power, exhaust, and compression
intake, exhaust, power
and compression
intake, compression, power, and exhaust
6. During the power stroke, the intake and exhaust valves are, respectively,
closed and opened
opened and closed
closed
and closed
7. The device for smoothing out the power impulses from the engine
is called the
crankshaft
camshaft
flywheel
clutch
8. The camshaft has a separate cam for each
engine valve
engine cylinder
piston
crankpin
9. Two parts that the I-head valve mechanism has that the L-head valve
push rod and rocker arm
mechanism does not are the
valve lifter and spring
camshaft and valve lifter
lock retainer{l~d
lock
[26]
\
1\
Automotive Fundamentals
10. In the ignition system the high-voltage surges produced by the coil
as the contact points separate are carried through the distributor cap
and rotor to the
ignition switch
spark plugs
battery
or source of power
capacitor
SUGGESTIONS FOR FURTHER STUDY
If you would like to study the engine and engine-component systems
further, there are several things you can do. For one thing, you can read
the Automotive Engines and the Automotive Electrical Equipment books
(two other books in the McGraw-Hill Automotive Mechanics Series).
Also, you can inspect your own and your friends' cars as well as cars and
engine components in the school automotive shop. You can go to a
friendly automotive service shop where repair work on engines is done,
By watching what goes on in the ordinary work of the day, you will learn
much about these automotive components. Perhaps you can borrow shoprepair manuals from your school automotive shop library or from the
car-dealer service shop. Your school may have cutaway models of engines or other automotive parts. By studying all this material, you will
better understand the construction and operation of the engine and thl'
engine-accessory systems.
[271
Z: Fuel-system funclamentals
THERE ARE two general types of fuel systems: the type with a
carburetor such as is used in most cars and the fuel-injection fuel
system that is beginning to come into common use. This chapter describes the fundamentals of the carburetor-type fuel system. Chapter
6 discussed the fuel-injection system.
§21. Purpose of the fuel system The fuel system is designed to
store liquid gasoline and to deliver it to the engine cylinders on the
intake strokes in the form of vapor mixed with air. The fuel system
must vary the proportions of air and gasoline to meet the requirements of different operating conditions. For example, during initial
starting with a cold engine, the fuel system must deliver a very
rich mixture (rich in gasoline) of about 9 pounds of air to 1 pound
of gasoline. Then, after the engine has warmed up, the mixture must
be leaned out (made less rich) to about 15 pounds of air to 1
pound of gasoline. For acceleration or high-speed operation, the
mixture must again be enriched.
§22. Components in the fuel system The fuel system (Fig. 2-1)
consists of the fuel tank, fuel gauge, fuel pump, carburetor, intake
manifold, connecting fuel lines, and the accelerator pedal and linkage. The accelerator pedal controls the amount of air-fuel mixture
entering the engine cylinders, and thus the amount of power the
engine produces. The fuel tank prOVides a reservoir, or storage space,
for gasoline. The fuel gauge has an indicator needle on the car
dash to indicate how full the fuel tank is. The fuel pump delivers
gasoline from the fuel tank to the carburetor, and the carburetor
mixes the gasoline with the air passing into the engine.
[281
§2~
Fuel-system Fundamentals
r:~
. .- . GAS UNE
GASTANK""""""'__
TAIL PIPE
r
MUFFLER
FIG. 2-1. Fuel system in phantom view.
§23. Atoms and elements Before we go into detail on how the carburetor and fuel system operate, let us talk about something that,
at first, may seem unrelated to the subject. We refer to atoms
and elements. As we look around us, we can see thousands of
different substances and materials, from wood to steel, from glass
to cloth, from gasoline to water. Yet the amazing fact is that all
these many substances are made out of only a few different types
of "building blocks" called atoms.
Actually, there are about ninety different kinds of atoms. Each
has a special structure that makes it different from other atoms,
and each has a special name such as iron, copper, hydrogen, sulfur,
tin, oxygen, and so on. A piece of iron, for example, is made up
entirely of one particular variety of atom. A quantity of the gas
oxygen is made up of a great number of another type of atom.
Any substance made up entirely of only one type of atom is called
an element. The table on page 30 lists a number of the more common elements.
The ninety some kinds of atoms can combine in many ways to
form hundreds of thousands of different combinations, or compounds. We can compare this to the 26 letters of the alphabet,
which can be combined in many ways to form the thousands of
words in our language. Thus, salt, water, wood, glass, gasoline, the
very blood and bones in our bodies are made up of compounds
produced by the combining of a few types of atoms. Salt is made
up of atoms of the elements sodium and chlorine. Water is made
up of atoms of the elements of hydrogen and oxygen.
[29]
§24
Automotive Fuel, Lubricating, and Cooling Systems
TABLE OF ELEMENTS
Name
Symbol
Atomic
number
Approximate
atomic weight
Electron
arrangement
Aluminum
AI
13
27
'2)8)3
Calcium
Ca
20
40
'2)8)8 )2
Carbon
C
6
12
·2)4
Chlorine
CI
17
35.5
,2)8 )7
Copper
Cu
29
63.6
'2)8)18)1
Hydrogen
H
Iron
Fe
26
56
'2)8) 14)2
Magnesium
Mg
12
24
'2)8)2
Mercury
Hg
80
200
Nitrogen
N
7
14
'2)5
Oxygen
0
8
16
'2)6
Phosphorus
P
15
31
'2)8)5
Potassium
K
19
39
'2)8)8)1
Silver
Ag
47
108
Sodium
Na
11
23
'2)8) 1
Sulfur
S
16
32
,2)8 )6
Zinc
Zn
30
65
'2)8)18)2
·1
.2)8)18)32)18)2
'2)8)18)18)1
§24. Size of atoms Individual atoms are far too small to see. There
are billions upon billions of atoms in a single drop of water. A
cubic inch of the gas hydrogen (at a temperature of 32° and at
atmospheric pressure) contains about 880,000,000,000,000,000,000
(880 billion billion) atoms. To give you an idea of how small atoms
really are, suppose we could expand this cubic inch until it was
large enough to contain the earth. That means each edge would
measure 8,OQO miles (instead of an inch). If the atoms were expanded in proportion, each atom would then measure about 10
inches in diallleter.
[30]
§25
Fuel-system Fundamentals
§2S. Atomic structure All of us, in this atom-bomb age where
"splitting the atom" is commonplace, have heard something of the
atom. We have mentioned that there are more than ninety varieties
of atoms. But basically, all atoms are composed of no more than
three fundamental particles called electrons, protons, and neutrons.
For instance, the hydrogen atom is made up of a proton at its center
(or nucleus) and an electron circling the proton at high speed
(Fig. 2-2). The proton has a charge of positive electricity (indicated
by a
sign). The electron has a charge of negative electricity (indicated by a - sign). There is a strong attraction between positive
and negative charges; this attraction tries to pull the electron into
the nucleus. But balancing this pull is the tendency that the electron
has to flyaway from the nucleus due to its rotary motion (that is,
+
FIG. 2-2. The hydrogen atom consists
of two particles, a proton at the center,
or nucleus, and an electron that circles
the proton.
+- means plus or positive
- meons minus or neqat/ve
the centrifugal force). This is the same balancing of forces you get
when you whirl a ball on a rubber band around your hand (Fig.
2-3). The rotary motion (or centrifugal force) tends to move the
ball away from your hand, but the rubber band (or attractive force)
keeps the ball moving in a circle around your hand.
The helium atom (helium, like hydrogen, is a gas) has 2 protons
in its nucleus and 2 electrons circling the nucleus. In addition, it has
2 neutrons in its nucleus (Fig. 2-4). The apparent function of the
2 neutrons is to hold the two protons together, though how they
do this is not known. But if the neutrons were absent, the
protons would fly apart, and there would be no helium atom. The
reason the two protons would fly apart is that their positive
charges repel each other, if the neutrons are not present. The
neutrons are neutral electrically; they have nO electric charge.
The atoms of the other elements are still more complicated than
the hydrogen atom; they have more protons, more neutrons, more
[31]
§26
Automotive Fuel, Lubricating, and Cooling Systems
electrons. Lithium (a light metal), for example, has 3 protons, 4
neutrons, and 3 electrons. Next comes beryllium (another light
metal) with 4 protons, 5 neutrons, and 4 electrons; boron with 5
protons, 5 neutrons, and 5 electrons; carbon with 6,6, and 6;
nitrogen with 7,7, and 7; oxygen with 8,8, and 8. Note that each
atom normally has the same number of electrons as protons. This
makes the atom electrically neutral since there is a negative electrical charge (or electron) for every positive charge (or proton).
§26. Molecules We have already mentioned that the many substances, or compounds, in the world are made up of different
combinations of atoms. Whenever two or more atoms combine,
ELECTRONS
FIG. 2-3. The electron in a hydrogen atom
FIG.
2-4. A helium atom.
circles the proton like a ball on a rubber
band swung around the hand.
they form a larger particle called a molecule. This is like combining
letters to form words. For example, when two atoms of hydrogen
and one atom of oxygen are combined, a molecule of water is
formed. When an atom of carbon is combined with two atoms of
oxygen, a molecule of carbon dioxide is formed. There are literally
millions of combinations, or molecules, that the various elements
can form. Some molecules have only two or three atoms, other
molecules may contain tens of thousands of atoms. The molecules
of albumin (a constituent of blood plasma) have more than ten
thousand a~oms.
When atoms combine to form molecules, or molecules are
changed by the addition or subtraction of atoms, the action is
[32J
Fuel-system Fundamentals
§27
called a chemical reaction. In other words, the atoms react with
each other.
§27. Combustion Combustion, or fire, is a common chemical reaction that involves atoms of the gas oxygen and atoms of other
elements such as hydrogen or carbon. Combustion takes place in
the engine cylinders. You will recall that air and gasoline vapor are
mixed in the carburetor and then the mixture is ignited, or set on
fire, in the engine cylinders. The air contains oxygen (about onefifth of the air is oxygen). Gasoline is made up essentially of
hydrogen and carbon molecules (and thus it is called a hydro-
carbon).
An oxygen atom has eight protons and eight neutrons in its
nucleus, and eight electrons circle the nucleus in two separate
paths, or orbits (Fig. 2-5). The inner orbit has 2 electrons. The
FIG. 2-5. An atom of oxygen.
outer orbit has 6 electrons. But the outer orbit has "room" for 8
electrons. It will, in fact, take on 2 additional electrons if free
electrons are nearby. The hydrogen atom has 1 proton in its nucleus
and 1 electron, as has already been mentioned.
When the gasoline burns, its molecules split into hydrogen and
carbon atoms. Then these atoms combine with oxygen atoms. For
instance, when the hydrogen atoms and oxygen atoms combine,
the action is about as follows. Two hydrogen atoms lose their
electrons as an oxygen atom "grabs" these "lost" electrons. The 2
electrons "fill up" the outer electron orbit of the oxygen atom. But
this gives the oxygen atom two negative electric charges. Meantime, the 2 hydrogen atoms are left with positive electric charges
(from their protons). The resulting electrical attraction between
the hydrogen and oxygen atoms causes them to combine into a
(33]
Automotive Fuel, Lubricating, and Cooling Systems
§28
molecule with the chemical symbol H 2 0 and the common name
water (Fig. 2-6).
At the same time, the carbon atoms are combining with oxygen
atoms. A carbon atom has 6 protons and 6 neutrons in its nucleus
and 6 electrons circling the nucleus in two orbits. In the combustion
process, the 4 electrons are "grabbed" by 2 oxygen atoms somewhat as shown in Fig. 2-7. Then, because of the resulting positive
and negative charges of the carbon and oxygen atoms, they
OXYGEN
HYDROGEN
2-6. An atom of oxygen uniting
with two atoms of hydrogen to form
a molecule of water (H,O).
FIG.
FIG. 2-7. One atom of carbon uniting
with two atoms of oxygen to form a
molecule of carbon dioxide (C02).
combine. One carbon atom combines with 2 oxygen atoms to form
carbon dioxide, or C02.
To sum up, in the combustion process in the engine cylinders,
the oxygen in the air unites with the hydrogen and carbon atoms in
the gasoline to form H 2 0 and C02 (water and carbon dioxide).
§28. Heat During combustion, as described in the previous section,
a great deal of heat is produced. All of us have a general idea of
what is meant by the word "heat." But the scientific explanation of
the word may not be familiar to us. For actually, to heat a substance
is to set the molecules of that substance into more rapid motion.
We tend to think that the molecules of a piece of wood or iron
(34)
,
Fuel-system Fundamentals
§29
or any other solid are motionless. However, they are in motion,
even though they move in rather restricted paths. But the higher
the temperature, the faster the motion of the molecules. When iron
is heated to a high enough temperature, the molecules are moving
so fast that the iron actually melts.
§29. Change of state When iron, or ice, or any similar solid melts,
it undergoes a change of state (it changes from a solid to a liquid).
Then, if it is further heated, it undergoes another change of state
(from a liquid to a vapor). Conversely, if the vapor is cooled, it will
change back to a liquid, and on further cooling, back to a solid.
All these changes are simply indications of the change in the speed
of the molecular motion.
For example, in ice, the water molecules are moving slowly and
in restricted paths. But if ice is heated in a pan over a fire, the
molecules will move faster and faster. As this happens, the molecules begin to break out of their restricted paths; the ice melts.
Then, presently, the molecules are moving so fast that they jump
clear of the water; the water boils, or turns to vapor.
Let us take another look at our pan of ice which changes to
water and then to vapor. The fire under the pan is produced by
oxygen atoms uniting with carbon and hydrogen atoms. Regardless
of what fuel is used (gasoline, coal, wood, gas, kerosene, oil), there
are hydrogen and carbon atoms in it that unite with the oxygen in
the air as already described (§27). The H20 and C02 molecules
that are formed during this process are very fast-moving. As the
molecules form, they dart oH in all directions. Many of them
bombard the bottom of the pan, almost like so many tiny baseballs
thrown against a barn door. This bombardment sets the molecules
of metal forming the pan into rapid motion (the pan gets hot). The
metal molecules, in turn, hammer against the ice molecules, setting
them into rapid motion. The ice melts. Then, as the bombardment
continues, the water boils.
NOTE: This is only a partial explanation of what takes place in a
fire. In addition to the fast-moving molecules, other effects are produced by the fire. These eHects are known as radiations. We see
some of these radiations as light and feel other radiations as heat.
Any modern high school physics book will describe these radiations
in detail.
[351
§30
Automotive Fuel, Lubricating, and Cooling Systems
A steel rod that measures
exactly 10 feet in length at 100°F will measure 10.07 feet in length
at 1000°F. The rod expands and gets longer as it is heated from
100 to 1000°F. The reason for this is that as the material becomes
hotter, the molecules move faster and faster. If the steel is heated
enough, it will melt. But even before this happens, the steel expands a little. This is because as the molecules move faster and
faster, they must have more room. They "push" adjacent molecules
away, so that all molecules, in effect, spread out, and expansion
takes place.
§30. Expansion of solids due to heat
§31. Expansion of liquids and gases due to heat Liquids and gases
also tend to expand when heated. A cubic foot of water at 39°F
will increase in volume to 1.01 cubic feet when heated to lOO°F. If
you had a cubic foot of air at 32°F and increased its temperature to
100°F, holding the pressure constant, you would find that its
volume had increased to 1.14 cubic feet. These expansion effects
result from more rapid molecular motion that tends to push the
molecules farther apart so that they spread out and take up more
room.
§32. Increase of pressure with temperature You get a different
effect if you hold the volume constant while the cubic foot of air
is heated from 32 to lOO°F. If we started with a pressure of 15
FIG. 2-8. Gas pressure in a container is the result of unending bombardment of the inner sides of the container by
the fast-moving molecules of gas. This bombardment is
shown on one side only of the container for simplicity. It
actually takes place against all the inner sides. The molecules are shown tremendously enlarged. There are, of
course, almost countless billions of molecules in action, and
not a few as shown.
psi (pounds per square inch), we would find that the pressure had
increased to about 17 psi at lOO°F. This is further evidence of the
molecular nature of heat. Actually, the pressure is due to the endless
bombardment of the sides of the container by the fast-moving
molecules of air or gas in the container (Fig. 2-8). Of course, a few
molecules ~:)Umping
against the sides of the container would show
However, since there are billions upon billions of
little ef~t:
[36]
\.
Fuel-system Fundamentals
§34
molecules bumping the walls, their combined "bumps" add up to a
definite "push," or pressure.
As temperature increases, the molecules of air are moving faster.
They bump the walls of the container harder and more often, thus
registering a stronger "push," or greater pressure.
In a similar way, when the molecules are pushed closer together
(that is, when the air in the container is compressed), the molecules bump into each other and into the walls of the container more
often. This more intense bombardment corresponds to a greater
pressure.
§33. Gravity Let us get away from molecules for a moment and
talk about gravity. Gravity causes the stone we drop to fall to the
earth. It makes the rain fall and the automobile coast down the
hill. Conversely, it makes you work harder when you climb stairs
and makes the engine work harder when pulling the car up a hill.
Gravity is the attractive force between all objects. We normally
measure gravity in terms of weight. When we put an object on a
scales and note that it "weighs" 10 pounds, we are actually saying
that the object has sufficient mass for the earth to register that
much pull on it. If the object had twice as much mass, then the
pull, or weight, would be 20 pounds.
§34. Atmospheric pressure We do not usually think of the air
around us, our atmosphere, as having any weight. But since it is a
substance (composed of gas molecules) and since the earth attracts
it (or attracts each molecule), it does have weight. At sea level,
and at average temperature, a cubic foot of air weighs about I}!
ounces (or 0.08 pound). This does not seem like very much. But
when you consider that the atmosphere (the blanket of air surrounding the earth) extends upward many miles, you can see that
the total effect is large. For there are, in effect, thousands upon
thousands of cubic feet of air, piled one on top of another, each
adding its weight. This total weight, or downward push, amounts to
about 15 psi (pounds per square inch) at sea level. This amounts to
2,l60 pounds, or more than a ton, of pressure per square foot (2,000
pounds = 1 ton).
Atmospheric pressure is not constant. It changes with the
weather. It also varies with height above sea level (on a mountain
or in a plane). The higher you climb, the lower the pressure; there
[37]
§35
Automotive Fuel, Lubricating, and Cooling Systems
is less air above you to press down on you. At 30,000 feet above
sea level, the air pressure is down to about 5 psi. At 100,000 feet
altitude, the pressure is no more than 0.15 psi. The farther out from
earth, the less air, and therefore less air pressure, there is. A few
hundred miles from the earth's surface there is practically no air at
all; there is simply a vacuum.
NOTE: During hot weather, the air expands and becomes lighter.
This means the atmospheric pressure is reduced. Cooled air is
heavier and increases atmospheric pressure. Varying air temperatures (due to the amount of heat the air gets from the sun) do more
than cause changing atmospheric pressure. The lighter air rises;
the heavier air sinks; and the varied movements of the air give rise
to our changing weather.
§35. Vacuum As we mentioned in the previous section, absence
of air or other material substance is called vacuum. We can create
a partial vacuum on the earth, but our best vacuum is not so good
as the vacuum far out in space, hundreds of billions of miles away
from the earth. The automobile engine is in one sense a vacuum
producer. Every time a piston moves down in a cylinder on the
intake stroke, it produces a partial vacuum in the cylinder. As the
piston moves down, it leaves "nothing" behind it. This "nothing" is
the partial vacuum. Let us look at this from the standpoint of the
molecules. We know that the air is made up of molecules or atoms
of various gases, moving about in all directions. When the piston
moves down, the gas molecules in the upper part of the cylinder
are given more room to move around in. They spread out to occupy
more or less uniformly the increasing space (as piston moves
down). Actually, what this means is that the distance between the
molecules increases. The greater the distance between molecules,
the higher the vacuum.
As the vacuum increases in the cylinder (due to piston moving
down), the atmospheric pressure outside the engine pushes air into
the cylinder. This air moves through the carburetor and past the
opened intake valve. Atmospheric pressure always tries to push
air into any space where vacuum exists. Following sections explain how the air movement through the carburetor causes gasoline
to be discharged into the air stream to produce a combustible airfuel mixture.
[38]
\
'~
Fuel-system Fundamentals
§35
CHAPTER CHECKUP
NOTE: Since the following is a chapter review test, you should review
the chapter before taking the test.
Once more, you will want to check up on how well you are remembering the material you have been reading. The questions that follow wiB
help you check yourself so you will know whether you remember the
facts discussed in the chapter you have just completed. In addition, since
the questions are on the most important facts, they serve as a review of
those facts. But don't be discouraged if you cannot answer all the questions offhand. Few people can remember everything they read, especially
after reading it only once. If any of the questions stump you, just turn
back into the chapter and reread the pages that will help you answer the
questions.
Completing the Sentences
The sentences below are incomplete. After each sentence there are
several words or phrases, only one of which will corrctly complete the
sentence. ·Write each sentence down in your notebook, selecting the
proper word or phrase to complete it correctly.
1. A substance made up entirely of only one type of atom is called
a particle
a molecule
an element
2. The three fundamental particles of which atoms are composed are
3.
4.
5.
6.
7.
8.
molecules, atoms, and electricity
electrons, protons, and neutrons
positives, negatives, and molecules
In the chemical reaction known as combustion, each oxygen atom
normally take on
1 electron
2 electrons
2 protons
2 neutrons
Since gasoline is made up essentially of hydrogen and carbon moleliquid
gas
hydrocarbon
carbohycules, it is a
drogen
Two of the products formed when gasoline burns are
oxygen
and hydrocarbon
carbon and oxygen
water and carbon
dioxide
water and oxygen
One way of looking at heat is to say that with increasing temperature,
the
molecules move faster
molecules move slower
molecules vaporize
As the temperature of the gas in a closed container is increased, the
increasing speed with which the molecules are moving produces the
effect of a
pressure increase
pressure decrease
pressure loss
vacuum increase
Atmospheric pressure is produced by the gravitational attraction of
[39]
Automotive Fuel, Lubricating, and Cooling Systems
vacuum
air
air pressure
weight of air
9. As air is heated, it
expands and becomes heavier
expands
and becomes lighter
contracts and becomes heavier
10. When there are relatively few molecules, widely scattered, the convacuum
pressure of air
pump acdition is called a
tion
space
the earth on the
SUGGESTIONS FOR FURTHER STUDY
If you are interested in the basic principles discussed in the chapter
you have just finished, you might like to study them further. Almost any
up-to-date high school physics book will give you much additional information on the principles covered in the past few pages. The Automotive Engines book (another book in the McGraw-Hill Automotive Mechanics Series) has additional explanations of the prinCiples. Your local
library probably has several physics books you will find of interest. In
addition, if you have a chance, you could talk over various paints that
may not be clear to you with your local high school science or physiCS
teacher. Teachers are almost always fine people who are sincerely interested in helping you gain more knowledge and thereby better yourself.
[40]
\
3: Fuel-system operation
THIS CHAPTER describes the operation of carburetor-type fuel
systems. We have already noted that the automotive fuel system
consists of the fuel tank, fuel gauge, fuel pump, carburetor, intake
manifold, connecting fuel lines, and the accelerator pedal and linkage (Fig. 2-1). Now, in the pages that follow, the purpose and operation of each of these is described in detail.
§36. Fuel tank The fuel tank (Fig. 3-1) is usually located at the
rear of the vehicle and is attached to the frame. It is a storage tank
for fuel, made of sheet metal. It sometimes contains a number of
bames, or metal plates, attached to the inner surface of the tank,
parallel to the ends. These plates have openings through which the
fuel can pass. Their main purpose is to prevent sudden surging of
FilTERING ELEMENT
FUEL GAUGE
FIG. 3-1. Fuel tank, partly cut away to show filtering element and drain plug.
(Plymouth Division of Chrysler Corporation)
[41]
§37
Automotive Fuel, Lubricating, and Cooling Systems
the fuel from one end of the tank to the other when the car rounds
a corner. The filler opening of the tank is closed by a cap, and the
tank end of the fuel line is attached at or near the bottom of the
tank. Usually, this line enters the tank at some point slightly
above the bottom, so that dirt or water that has settled to the
bottom of the tank will not enter the fuel line.
The fuel tank contains the tank unit of the fuel-gauge system
(§38) and usually a filtering element of some kind to filter dirt
from the fuel and prevent it from entering the fuel line. The filter
is located at the point where the fuel line is attached to the tank;
all fuel leaving the tank must pass through the filter. The fuel-tank
cap has a vent which permits air to enter the tank as fuel is withdrawn. If this vent were to become stopped up, a vacuum would
be created in the tank that would prevent normal delivery of fuel
to the fuel pump and carburetor.
§37. Fuel filters and screens Fuel systems include filters and
screens of various types to prevent dirt or grit in the fuel from
entering the fuel pump or the carburetor. The fuel pump has valves
that could be prevented from operating normally by particles of
dirt, while the carburetor contains fuel passages and jets that could
become clogged by dirt. 11). some systems the fuel filter is a separate
unit located in the fuel line. In many systems a filter is incorporated
in the fuel pump itself (see §39). In addition, the carburetor may
contain filter screens.
§38. Fuel gauge Years ago, the standard procedure for finding out
how much gasoline remained in the tank was to remove the tank
cap and insert a measuring stick. Today, however, the driver merely
looks at the gauge on the dash of the vehicle. Gasoline, or fuel,
gauges can be divided into two general classifications, hydrostatic
and electric. The hydrostatic fuel gauge, not in general use today,
will be considered only briefly.
1. Hydrostatic. The hydrostatic fuel gauge depends upon the
pressure of the fuel in the tank on a column of air. The column
of air is contained in a vertical tube open at the end inserted in the
fuel. The fuller the tank, the more pressure the fuel exerts on the
column of air. The upper end of the air tube is connected to an
indicating t\1be on the dash that is partly filled with colored liquid.
Increased" air pressure, caused by a full fuel tank, pushes the
[42]
.
Fuel-system Operation
"1;lOr,.-4. ./d.b < 11
5tv~l!',_
11
h
,
t'
.
,.,
§38icsl:! !
colored liquid high in the indicating tube. As the fuel~v
the air pressure decreases, allowing the colored liquid to drop to' (i. JO
a lower level in the indicating tube. The air in the air tube in the
tank is continually replenished by a splash cup near the top of the
tank, into which gasoline is constantly splashed by the car movement. The gasoline drains back down into a tube attached to the
splash cup, carrying with it air, which is released at the bottom of
the air tube.
2. Elect1'ic. Electrically operated fuel gauges may be divided into
two types, the balancing-coil type and the bimetal-thermostat type.
drop<'::tSit}
RESISTANCE
,.---\---'-.I...74b--"- SLI DING
CONTACT
DASH UNIT
IGNITION
COlIC
FIG. 3-2. Schematic wiring circuit of
balancing-coil
system.
fuel-gauge
indicating
SWITCH
3·3. Schematic wiring circuit of
thermostatic fuel-gauge indicating
system.
FIG.
The balancing-coil type uses a variable resistance, or rheostat, in
the tank and two coils of wire placed at a gO-degree angle to each
other in the dash indicating unit (Fig. 3-2). The movement of a
float up or down in the tank as the tank is filled or emptied causes a
sliding contact to move around to various positions on the resistance. This allows the resistance to pass more or less electric current,
passing more as the tank empties and less as the tank fills. As the
tank empties, more and more of the electric current passing through
the "empty" coil from the battery then flows through the resistance
instead of through the "full" coil. Consequently, the magnetic
strength of the "fuU" coil is weakened, allowing the armature to
which the indicating needle is fastened to be pulled around by the
magnetic force toward the "empty" coil. But when the tank is filled,
the sliding contact moves around so that resistance is increased.
[43]
Automotive Fuel, Lubricating, and Cooling Systems
§39
Most of the current passing through the "empty" coil then passes
through the "full" coil. This produces a different magnetic pattern
which turns the armature and needle toward the "full" coil. Note
that the fuel-gauge indicator is connected to the battery through
the ignition switch. This prevents any drain on the battery when
the ignition switch is turned off and the engine is not running. More
data on magnetism and resistance are contained in another book
in the McGraw-Hill Automotive Mechanics Series (Automotive
Electrical Equipment).
The bimetal-thermostat type of fuel gauge depends upon the
heating and bending of two bimetal-thermostat blades, one in the
tank unit and one in the dash indicating unit (Fig. 3-3). Each
bimetal-thermostat blade consists of two strips of different metals,
welded together. When heated, the two metals expand at different
rates, causing the blade to bend. Around each blade is a heater
wire. Both wires carry the same amount of current, and thus each
blade is heated the same amount. Consequently, each blade will
bend the same amount. When the tank is filled, a cam attached to
the float in the tank moves a contact button that imposes an initial
distortion on the tank-unit blade. This blade must then heat considerably before it bends enough to move away from the contact
button. While it is heating, the blade in the dash unit also heats,
bending so that the indicating needle is moved toward "full." When
the tank-unit blade has bent enough to move away from the contact
button, current stops flowing, and the blade cools and moves back
to the button. Current again flows; the blade heats and bends away
again. As the tank empties, the float drops and the cam moves
around so that it imposes less initial distortion on the blade. Thus,
the blade does not have to heat quite as much to bend further and
move away from the contact button: less heating is required to
keep the tank-unit blade vibrating and opening and closing the
circuit. Consequently, the dash-unit blade is heated less and does
not bend so much, so that the needle moves back toward "empty."
Earlier fuel systems depended on gravity or air
pressure to cause the flow of gasoline from the gasoline tank to the
carburetor. In the gravity system the fuel tank had to be located
above the carburetor, and the fuel ran down from the tank to the
carburetor by force of gravity. It is no longer in common use be[44]
§39. Fuel pump
I
§39
Fuel-system Operation
cause of its disadvantages, among which were the uncertainty of
having enough fuel when climbing a hill and the fire hazard from
the necessary closeness of the tank to the engine. The pressure
system utilized an air pump that built up pressure within the fuel
tank, forcing the fuel from the tank to the carburetor. This design
also is no longer in common use because of the complexity of the
system, which required two lines to the tank and a good tank seal.
Outlet valve-----....
Valve and cage
assembly---,
Valve and cage
,gasket ----_..,_
Drain Screw
gasket-~
Cover plate
ccrpSCrew
Cap screw
gorsket
l---Screen
Cover p/orfe
Cover p/afe
gasket
spring
Rocker arm
pin------'
FIG, 3-4. Sectional view of a fuel pump. Inlet valve is to right and outlet valve
to left. (AC Spark Plug Division of General Motors Corporation )
Modern fuel systems use a simple fuel pump (Figs. 3-4 and 3-5)
to pump the fuel from the tank and deliver it to the carbmetor.
The fuel pump is usually mounted to the side of the engine block,
well down, to avoid excessive temperatmes from the engine (Fig.
3-6). A rocker arm from the pump extends through an opening provided for it in the side of the engine block and rests against an
eccentric (or offset ring ) on the camshaft. Thus, when the camshaft rotates, the eccentric will cause the rocker arm to rock back
and forth. A rocker-arm spring keeps the rocker arm in constant
contact with the eccentric.
The rocker arm is linked to a diaphragm. The diaphragm is made
[45]
Automotive Fuel, Lubricating, and Cooling Systems
§39
of a special flexible clothlike material that is not affected by gasoline. It is fastened between two cuplike plates at its center. Its
outer edge is clamped between the upper and lower parts of the
pump. The diaphxagm is spring-loaded so that it attempts to remain at its upper limit of travel. However, the movement of the
rocker arm, acting tiuough the link, pulls the diaphragm down.
This movement tends to create vacuum in the fuel-pump chamber
which is just above the diaphragm. As we have ah'eady noted (in
Oil seal
Rocker arm
link
Boil screw
FIG. 3-5. Sectional view of a fuel pump. Arrows show direction of fuel flow
through pump. (Studebaker-Packard CorlJoration)
§35), atmospheric pressure attempts to push air toward any space
where there is a vacumTI. In the fuel system the only place the air
can act is in the fuel tank. An air vent in the fuel tank admits
atmospheric pressure. The atmosphere therefore pushes toward the
vacuum in the fuel pump, pushing fuel ahead of it.
As the fuel is pushed toward the vacuum created by the downward movement of the diaphragm, tile inlet valve is forced down
off its seat. Fuel therefore is pushed into the pump chamber (just
above the diapluagm). Now, a moment later, as the camshaft revolves, the high area of the eccentric moves away from the rocker
arm. The 'rocker arm therefore rocks toward the camshaft, releasing
[46J
\
\
Fuel-system Opemtion
§39
the diaphragm. The diaphragm is pushed upward by its spring.
This produces a pressure of several pounds per square inch (psi)
in the pump chamber. The pressure forces the inlet valve closed
and forces the outlet valve open. Diaphragm-spring pressure then
forces fuel through the outlet valve, through the connecting line,
and into the carburetor.
ignifion
ctisfribufor.
FIG. 3-6. Mounting of fuel pump on engine. Other accessories, including water
pump, ignition distributor, starting motor, and generator are also shown.
(Buick Motor Division of Ge /l eral Motors Corporation)
As will be explained in the section on carburetors, the fuel from
the fuel pump is delivered to a float bowl, or reservoir, in the carburetor. The float bowl has a needle valve that shuts off the flow ui
fuel when the bowl is full. When this happens, the fuel pump stops
delivering fuel to the float bowl. During this interval the rocker arm
continues to rock. However, the diaphragm remains at or near the
lower limit of its travel; its spring cannot force the diaphragm upward so long as the float bowl will not accept further fuel. However,
[471
Automotive Fuel, Lubricating, and Cooling Systems
§40
as the carburetor uses up fuel, the needle valve in the float bowl
opens to permit the fuel pump to deliver fuel. Now the diaphragm
can move up (on the rocker-arm return stroke) to force fuel into
the carburetor float bowl.
INLET CYCLE
OUTLET CYCLE
FIG. 3-7. Sectional views of a fuel pump showing the inlet and outlet cycles.
(Mercury Division of Ford Motor Company)
Figure 3-7 illustrates a fuel pump of a somewhat different design
from those shown above. However, it is essentially identical in
operation to the ones previously described.
§40. Combination fuel and vacuum pumps Combination fuel and
vacuum pumps contain not only the fuel pump (as described
above) for supplying fuel to the carburetor, but also a vacuum
pump that provides vacuum to operate the windshield wipers (Fig.
3-8) . A majority of windshield wipers are designed to operate on
vacuum. Many obtain their source of vacuum from the intake manifold. However, since intake-manifold vacuum varies considerably
with diHerent operating conditions, there are times when the
vacuum will not be sufficient to operate the windshield wipers.
This is most noticeable when the throttle is suddenly opened, as
for instan<i_e when accelerating to pass another car. During such
moents~
when clear vision is most needed, the reduction in vac\
uum (du~
, to opening the throttle) may cause the windshield
[48]
1\
\.
Fuel-system Operation
§40
wipers almost to stop. The vacuum pump (which is combined with
the fuel pump) provides a steadier source of vacmill1 and more
even operation of the windshield wipers.
__~-TOINAKE
MANIFOLD
FIG. 3-8. Cutaway view of fuel and vacuum pump. The vacuum unit is at the
top, the fuel pump at the bottom. (Mercurlj Division of Ford Motor Company)
In the combination pump shown in Fig. 3-8, the lower part is the
fuel pump, which operates as ah-eady explained, and the upper
part is the vacuum pump. You will note that it is very similar in
appearance to the fuel pump. It contains a diaphragm actuated by
a second link from the rocker arm, and two valves. The diaphragm
and valves operate in the same manner as those in the fuel pump.
The essential difference is that the vacuum pump pumps air instead
[49]
§41
Automotive Fuel, Lub1"icating, and Cooling Systems
of fuel. Air is pumped out of the windshield-wiper motor, producing the vacuum that causes the windshield wiper to operate.
§41. Electric fuel pumps The elechic fuel pump (Fig. 3-9) found
on some heavy-duty equipment, such as trucks and busses, uses
elechicity from the battery (or generator) to operate a bellows and
thereby supply the carburetor with fuel from the fuel tank. The
bellows serves the same purpose as the diaphragm in the fuel
(a)
(b)
3-9. (a) External and (b) sectional views of electric fuel pump. The
bellows and electromagnet are in the lower part of the pump.
FIG.
pumps previously considered. As it expands 01' collapses, it "pulls"
fuel in or forces it out. The expansion or contraction is produced
by an electromagnet which is repeatedly connected to or disconnected from the battery. The electromagnet becomes connected to
the battery when the ignition switch is turned on. When this happens, the electromagnet is energized. This draws the electromagnet
armature downward so that the bellows expands and produces a
vacuum that causes fuel to pass from the fuel tank to the fuel pump.
The inlet valve opens to permit tlle fuel to enter. As the armature
reaches the lower limit of its travel, it opens contact points which
[OOJ
\
ANGRAU
~
"
~
Central LIbrary
RaJendranagar
11111111111111I11111111I1
Fuel-system Operation
§42
open the circuit to the battery. The electromagnet therefore becomes disconnected and de-energized.
Now, the pump return spring pushes upward on the armature
and bellows, collapsing the bellows and forcing the fuel in the bellows out through the outlet valve. As this happens, the inlet valve
is forced closed. The fuel passes from the fuel pump to the carburetor. As soon as the armature reaches the upper limit of its travel,
it closes the contact points so that the electromagnet is reconnected
to the battery, and the above cycle is repeated. This action continues as long as the ignition system is turned on. The frequency
with which the delivery stroke of the armature is repeated depends
upon the amount of fuel the carburetor and engine require. When
the engine is not using a great deal of fuel, the return spring collapses the bellows slowly since the needle valve in the carburetor
is preventing rapid delivery of fuel to the carburetor. But when
larger amounts of fuel are required, the bellows collapses more
rapidly, and the delivery stroke is therefore repeated more often,
to keep the carburetor supplied with fuel.
A great deal of air passes through an engine when
it is operating. As has already been mentioned, the fuel is mixed
with air in the carburetor and the mixture passes on into the engine
cylinders where it is ignited and burns. During normal running of
the engine, the carburetor supplies a mixture ratio of about 15: 1,
that is, 15 pounds of air for each pound of gasoline. To say it
another way, each gallon of gasoline requires as much as 1,200
cubic feet of air for normal combustion in the engine. As much as
100,000 cubic feet of air may pass through the engine every 1,000
car miles. This is a great volume of air, and it is apt to contain
large quantities of floating dust and grit. Since this dirt and grit
could cause serious damage to the engine parts if allowed to enter
the cylinders, an air cleaner is used to filter such particles from the
air. The air cleaner is mounted on the atmospheric side of the carburetor air horn. It consists of a large drum, the upper part of
which contains a ring of noninflammable filter material (fine-mesh
metal threads, or ribbons) through which the air must pass. This
material provides a fine maze that filters out the dust particles
(Fig. 3-lO). An oil-bath air cleaner is shown in Fig. 3-lO, while H.
heavy-duty horizontal cleaner is shown in Fig. 3-11. The oil-bath
§42. Air cleaner
[511
Automotive Fuel, Lubricating, and Cooling Systems
§42
FIG. 3-10. Carburetor air cleaner and intake silencer of the oil-bath type. It
incorporates an oil reservoir past which the air must flow. The sharp turn that
the air must take throws particles of oil from the oil bath up into the filter. Dust
that accumulates in the filter material is washed down into the oil reservoir by
the oil. (Oldsmobile Division of General Motors Corporation)
3-11. Air cleaner for an eight-cylinder engine. The space limitations under
the hood make is necessary to use a partly horizontal cleaner on this application.
(Oldsmobi{e t?ivision of General Motors Corporation)
FIG.
(52]
\,
Fuel-system Operation
§43
cleaner contains a reservoir of oil past which the air flows. The
moving air picks up particles of oil and carries them into the filter.
There the oil washes accumulated dust and dirt back down into
the oil reservoir. In addition to this washing action, the oiliness of
the filter material improves the filtering action.
The air cleaner has a second function; it muffles the noise resulting from the intake of air through the carbmetor and intake
manifold and past the intake valves. Without the air cleaner, the
sound of the intake of air could become quite noticeable and
annoying to the driver.
The air cleaner also acts as a flame arrester in case the engine
backfires through the carbmetor. Backfiring may occm at certain
times as a result of ignition of the air-fuel charge in the cylinder
before the intake valve closes. When this l1appens, there is a momentary flash-back through the intake manifold and carbmetor.
The air cleaner prevents the flame hom erupting from the carburetor and possibly igniting fuel or gasoline fumes on the outside
of the carbmetor.
§43. Intake manifold The intake ports in the side of the engine
block (or in the side of the head on overhead-valve engines) are
FIG. 3-12. Intake manifold for an L-head engine.
connected by the intake manifold to the carburetor. The air-fuel
mixture from the carburetor passes through the intake manifold to
the intake ports and through these ports to the engine cylinders
(when the intake valves are open). Figure 3-12 shows a typical
intake manifold for an L-head engine. Essentially, the intake manifold is nothing more than a series of passages leading from a central
[53]
Automotive Fuel, Lubdcating, and Cooling Systems
§44
point (where the carburetor mounts) to the intake ports in the
engine. The intake manifold is so designed as to aid in even distribution of the air-fuel mixture to the engine cylinders. In the design,
sharp corners are avoided. Sharp corners might set up eddy currents which could result in uneven mixture distribution; some cylinders might be "starved."
§44. Carburetor The carburetor (Fig. 3-13) mixes air and gasoline
in varying proportions for different operating conditions. As air
passes through the carburetor on its way to the engine, gasoline is
IDLE speeD ADJUSTING SCREW
FIG. 3-13. Exterior view of a typical carburetor. The climatic contwl (at top )
is the automatic choke.
fed into it through various circuits to be described below. The gasoline is fed intp the passing air as a fine spray; that is, it is atomized.
This causes the gasoline to evaporate very quickly, producing a
combustible ~ixture
of gasoline vapor and air.
[54]
/\
I
\
\
•
Fuel-system Operation
§47
When a liquid changes to a vapor (or undergoes a change of state) it is said to evaporate. Everyone is familiar
with evaporation. Water placed in an open pan will eventually disappear; it changes from a liquid to a vapor. Clothes are hung on a
line to dry; the water in the clothes changes to a vapor. When the
clothes are well spread out, they will dry more rapidly than when
they are hung closely or bunched together. This illustrates another
well-known fact about evaporation. The greater the surface exposed to the air, the more rapidly evaporation will take place. If
a pint of water is placed in a tall glass, it will take a long time to
evaporate. But if a pint of water is placed in a shallow pan, the
length of time required for the water to evaporate will be greatly
shortened (Fig. 3-14).
§45. Evaporation
FIG. 3-14. Water will evaporate
from the shallow pan faster than
from the glass: the greater the area
exposed to air, the faster the evaporation.
§46. Atomization Some early experimenters with gasoline engines
tried to charge the ingoing air with gasoline vapor by passing it
over pans of gasoline. This did not work very well because the
pans could not be made large enough to expose a sufficiently large
surface area of gasoline. The resulting mixture was too lean; it
had too small a percentage of gasoline vapor in it. Then it was
found that if the gasoline were sprayed into the passing air, adequate vaporization would take place. Whenever a liquid is sprayed,
it is turned into a great many tiny droplets. This effect is called
atomization because the liquid is broken up into small droplets
(but not actually broken up into atoms as the name implies). Each
droplet is exposed to air on all sides sO that it evaporates, or turns
to vapor, quickly. It is possible that an ounce of gasoline, broken up
into fine droplets by spraying, will actually expose several square
feet of surface area to air. Consequently, vaporization, or evaporation, takes place almost instantaneously.
§47. Carburetor fundamentals A simple carburetor could be made
from a round cvlinder with a constricted section, a fuel nozzle or
[55]
Automotive Fuel, Lubricating, and Cooling Systems
§47
tube, and a round disk, or valve, which could be tilted more or less
to open or close the round cylinder (Fig. 3-15). The round cylinder
is called the air hom, the constricted section the venturi, and the
valve the throttle valve. Figure 3-16 shows the throttle valve in
the closed position, the position at which it throttles, or shuts off,
the air flow through the air horn so that little air can get through.
The opened position is shown dotted. In the opened position, the
valve has little throttling effect; air can flow tlll'ough the air horn
freely.
Fvelnozzle
FIG. 3-15. Simple carburetor consist-
ing of air horn, fuel nozzle, and
throttle valve.
3-16. Throttle valve in air horn
of carburetor. When throttle is
closed, as shown, little air can pass
through. But when throttle is opened
(as shown dotted), there is little
throttling effect.
FIG.
1. Venturi effect. As air flows through, a partial vacuum is produced at the constriction, or ventUl'i. This vacuum causes the fuel
nozzle to deliver gasoline into the passing air. Let us examine these '
actions more closely. The venturi effect (of producing a vacuum)
can be illustrated by the setup shown in Fig. 3-17. In this illustration, three dishes of mercUl'Y (a very heavy metallic liquid) are
connected by tubes to an air horn with a venturi. The greater the
vacuum, the higher the mercury is pushed up in the tube by the
atmospheric pressUl'e acting on the sUl'face of the mercury in each
dish. Note that as air flows through the ventUl'i, the greatest amount
of vacuum ,is produced in the venturi. This vacUlun increases with
the speed ,?.f'the air flowing through the venturi.
[56]
},
\
\,
\
Fuel-system Operation
§41
The air is not a continuous fluid, or substance; it consists of
separate particles, or molecules. When we keep this in mind, the
venturi effect becomes more easily understood. For example, let
us follow two particles through the venturi and see what happens.
As air enters the top of the air horn, all the air particles are moving
downward toward the venturi at more or less uniform speed. However, if all particles are to move through the constriction, or venturi,
they will have to speed up and hurry through. Suppose we watch
------+
Air_
flow
FIG. 3-17. Three dishes of mercury and tubes connected to air horn show differences in vacuum by the distance mercury rises in tubes. Venturi has highest
vacuum.
two of the particles on their way through the venturi. One particle
is somewhat behind the other. The leading particle, entering the
venturi first, speeds up, tending to leave the second particle behind.
The second particle, entering the venturi, also increases in speed.
But the first particle has, in effect, a head start. The second particle
cannot catch 'up. They are farther apart in passing through the venturi than they were when entering the air horn. Now visualize a
great number of particles going through this same action, and you
can understand that in the venturi they are somewhat farther apart
than they were when they first entered the air horn. This is just
another way of saying that a partial vacuum exists in the venturi.
For, as we mentioned previously (§35), a partial vacuum is a thin[57]
§47
Automotive Fuel, Lubricating, and Cooling Systems
ning out of the air, a more than normal distance between the air
particles, or molecules.
2. Fuel-nozzle action. The partial vacuum occurs in the venturi,
where the open end of the fuel nozzle is placed. The other end of
the fuel nozzle is in a fuel reservoir (the float bowl) on the side
of the carburetor (Fig. 3-18). With a vacuum at the upper end of
the fuel nozzle, atmospheric pressure (working through a vent in the
£loat-bowl cover) pushes from the fuel reservoir up through
the nozzle and out into the passing air stream. The fuel leaves the
fuel nozzle in the form of a fine spray which rapidly turns into
vapor as the droplets of fuel evaporate. The more air that moves
through, the faster it moves and the greater the amount of fuel the
FIG. 3-18. The venturi, or constriction,
causes a vacuum to develop in the air
stream just below the constriction.
Then atmospheric pressure pushes fuel
up and out the fuel nozzle.
nozzle delivers (because higher air speed means a higher vacuum
in the venturi).
Fuel-nozzle action might be compared to drinking through a
straw. When you stop at the soda fountain and get a soda, you put
the straw in your mouth and "suck" on it. Actually, you create a
partial vacuum in your mouth by jaw and tongue movement. Atmospheric pressure then cooperates by pushing the liquid up
through the straw and into your mouth. In the same way, atmospheric pressure pushes fuel from the float bowl, or reservoir, up
through the fuel nozzle and into the vacuum of the venturi.
3. Throttle-valve action. As has already been mentioned, the
throttle valve can be tilted in the air horn to allow more or less
air to flow through. The throttle valve is a round disk mounted on
a throttle shaft. The shaft can be rotated to tilt the throttle valve.
When it i~ tilted to the position shown dotted in Fig. 3-16, a great
deal of ait . ca_n flow through. This produces a relatively high vacuum in the\venturi, and a great deal of fuel is delivered to the
[58]
't,
\
\
\
Fuel-system Operation
§48
passing air. When large amounts of air-fuel mixture are fed to the
engine, the engine develops a relatively high power output. This
means that the car tends to speed up, or accelerate. Linkage between the throttle shaft in the carburetor and the accelerator pedal
BEARING ASSEMBLY
-rLT_"'V,\~
:;~
CAR8URET0d,R
::::ER
.
\) 'jCREW
1
ACCELERATOR PEDAL
NUT
THROTTLE LEVER HOOK-UP
FIG. 3-19. Linkage between accelerator pedal and carburetor throttle valve.
in the driver's compartment for one car is shown in Fig. 3-19. The
linkage differs for different cars.
§48. Float bowl The float bowl serves as a constant-level fuel
reservoir. It is necessary for the fuel level in the float bowl to remain at a constant height, regardless of whether small amounts or
large amounts of fuel are being withdrawn. If the fuel level goes
too high, more fuel will be discharged through the fuel nozzle. On
the other hand, if the fuel level is too low, less fuel will be discharged. In either case, the proportions of fuel and air would not
be correct, and the engine would not operate properly.
To maintain the fuel level at a constant height, the float bowl
contains a float pivoted on an arm, and a needle valve and seat.
The needle valve is located at the inlet to the float bowl. Figure
[59]
I
!
I
Automotive Fuel, Lubricating, and Cooling Systems
§48
3-20 is a simplified drawing of a Boat bowl, while Fig. 3-21 is a
sectional view of an actual carburetor and Boat system. When the
engine is running, the fuel pump supplies fuel to the carbmetor,
and the fuel Bows through the inlet into the Boat bowl. If gasoline
FIG. 3-20. Simplified drawing of a
carburetor Boat system.
STRAINER
FLOAT NEEDLE
SEAT ............-....
FLOAT NEEDLE ___.._..,......
iiIP....-==-~
':!F,=-rl
__
FLOAT LEVER
FLOAT
FIG. 3-21. Sectional view of a carburetor, showing Boat system. Fuel enters
as shown by curved arrow. (Studebaker-Packard Corpomtion)
enters faster than it is being withdrawn (by the fuel nozzle), the
Boat bowl will fill up. As this happens, the Boat rises, lifting the
needle valve and forcing it tightly up into the needle-valve seat.
the inlet, preventing fmther delivery of fuel. But as
This closes ~f
soon as s01pe fuel is withdrawn, the fuel level falls, the Boat drops
[60]
\
\
\
\.
Fuel-system Operation
§49
down, the needle valve is lowered off its seat, and additional fuel
is delivered by the fuel pump. In actual operation, the fuel is
maintained at a practically constant level in the float bowl. The
float tends to hold the needle valve partly closed so that the incoming fuel just balances the fuel being withdrawn.
Mter the air-fuel mixtme has been bmned
in the engine cylinders, it is exhausted from the cylinders as the
§49. Exhaust system
FIG. 3-22. Exhaust system of an engine. ~
FIG. 3-23. Exhaust manifold for a six-
cylinder L-head engine with heat-control valve and parts in disassembled
view.
exhaust valves open on the exhaust strokes of the pistons. The
burned gases pass into the exhaust manifold and from there into
the exhaust pipe, the mumer, and the tail pipe (Eig. 3-22). The
exhaust manifold is essentially a series of passages for carrying the
[61]
§50
Automotive Fuel, Lubricating, and Cooling Systems
exhaust gases from the engine cylinders to the exhaust pipe. A
typical exhaust manifold is shown in Fig. 3-23. On L-head engines
the exhaust manifold is bolted to the cylinder block. On I -head, or
overhead-valve, engines the exhaust manifold is bolted to the cylinder head. The exhaust manifold is normally located under the intake manifold, and there is a connection between the two. The purpose of this connection is to supply heat to the intake manifold
(from the hot exhaust gases) when the engine is first started, to assure good vaporization of the gasoline entering the engine through
the intake manifold. This improves engine operation during the
cold-operation period. A following section discusses this matter in
detail.
On V-8 engines there are usually two exhaust manifolds, one on
each bank. The exhaust manifolds are mounted on the outsides of
the cylinder banks. Each has a separate exhaust pipe, but the two
exhaust pipes are connected together into a crossover pipe. The
crossover pipe is connected to a Single mumer and tail pipe. Thus
the exhaust gases from the two manifolds combine in the crossover
pipe and exhaust through the same mufBer. On some V-8 engines
two separate exhaust systems are used (§51).
§50. Muffler The mufBer (Fig. 3-24) is located under the car body
and is connected into the exhaust system between the exhaust pipe
and the tail pipe. It is designed to mume the noise of the engine
exhaust by gradually reducing the pressure of the exhaust gases
II
FIG. 3-24. Exhaust muffler in sectional view. The arrows show the path of
exhaust-gas How through the mufHer. (Chevrolet Motor Division of General
Motors Corporation)
[62]
\,
§51
Fuel-system Operation
as they leave the engine cylinders. Mufflers usually consist of a
series of holes, passages, and resonance chambers that absorb and
damp out the high-pressure surges introduced into the exhaust
system when the exhaust valves open.
§51. Dual exhaust system The dual exhaust system used on one
V-8 engine is shown in Fig. 3-25. Each exhaust manifold exhausts
into a separate exhaust pipe which, in turn, exhausts into its own
muffler, resonator, and tail pipe. The purpose of the resonators is
to reduce exhaust noises further. They are, in effect, secondary
mufflers. The use of two separate exhaust systems, one for each
bank of cylinders, improves the ability of the engine to "breathe."
That is, they allow the engine to exhaust more freely so that there is
less exhaust gas left in the cylinders at the ends of the exhaust
strokes. In other words, they lower the back pressure due to the
restricting effect of the exhaust system. With less exhaust gas in
the cylinders at the ends of the exhaust strokes, more air-fuel mixture can enter, and engine performance is improved. Adding a dual
exhaust system can improve engine output several horsepower.
CHAPTER CHECKUP
NOTE: Since the following is a chapter review test, you should review
the chapter before taking the test.
Here is your chapter checkup that gives you the opportunity to test
yourself on the chapter you have just finished. It is important to fix the
fundamental principles of the fuel system in your mind because understanding of carburetor actions depends on knowledge of these principles.
Thus, you will want to take the test below to determine whether you
remember the principles. Don't be discouraged if you cannot answer all
the questions. That simply means that you haven't quite fixed the facts
in your mind. Thus, all you have to do is go back over the chapter so
that you can get those facts memorized.
Unscrambling the lobs
When the two lists below are unscrambled and combined, they will
form a list of the various components of the fuel system and the jobs these
components do. To unscramble the lists, take one item at a time from the
list to the left, and then find the item from the list to the right that goes
with it. Write the result down in your notebook. For example, the first
item in the list to the left is "tank." When you look down the list to the
right, you can see that the only item that describes the job the tank has
[63J
Automotive Fuel, Lubricating, and Cooling Systems
'"0
>=:
ell
0.0
>=:
LE==;:j;g
~
\
\
\
[64]
\
),
,\
Fuel-system Operation
to do is "stores fuel." So you put the two together to form "tank stores
fuel."
tank
filter
pump
carburetor
gauge
air cleaner
filters air
mixes fuel and air
stores fuel
indicates fuel in tank
cleans fuel
delivers fuel to carburetor
Completing the Sentences
The sentences below are incomplete. After each sentence there are
several words or phrases, only one of which will correctly complete the
sentence. Write each sentence down in your notebook, selecting the
proper word or phrase to complete it correctly.
balancingcoil and hydrostatic
bimetal-thermostat and hydrostatic
balancing-coil and bimetal-thermostat
The tank unit of the balancing-coil fuel gauge contains a
variable resistance
bimetal thermostat
switch
capacitor
The tank unit of the bimetal-thermostat fuel gauge has
a variable resistance
a heating coil
a pointer
an armature
In the fuel pump, the rocker arm, which rests against an eccentric
on the camshaft, is linked to the
inlet valve
outlet valve
diaphragm
Fuel is delivered from the fuel tank to the fuel pump as the rocker
arm
pulls diaphragm down
releases diaphragm
closes inlet valve
Fuel is delivered from the fuel pump to the carburetor by the
rocker-arm pull
diaphragm-spring pressure
float-bowl vacuum
The device mounted on the carburetor air horn has two jobs, to
filter
filter fuel and silence intake
filter air and wash filter
air and silence intake
The breaking up of a liquid into fine droplets by spraying is called
vaporization
atomization
venturi effect
carburetion
A simple carburetor could be made from an air horn with venturi, a
throttle valve, and
a float bowl
throttle linkage
a fuel nozzle
The parts in the carburetor that permit or prevent fuel delivery, thus
maintaining proper fuel level in the reservoir, include the
inlet
float and needle
and outlet valves
fuel nozzle and venturi
valve
[65]
1. Electrically operated fuel gauges are of two types,
2.
3.
4.
5.
6.
7.
8.
9.
10.
Automotive Fuel, Lubricating, and Cooling Systems
SUGGESTIONS FOR FURTHER STUDY
In any automotive shop offering fuel-system service, you will probably
find worn-out fuel gauges and fuel pumps. Perhaps you will be permitted
to examine these units and possibly to tear them down so you can inspect the internal parts. Examining the parts will help you understand the
workings of the mechanisms. School automotive shops often have cutaway units that show the internal working parts clearly; these are very
helpful to the student. Automotive Electrical Equipment (another book
in the McGraw-Hill Automotive Mechanics Series) contains much additional material on electric fuel gauges and the principles on which they
operate. Also, the manufacturers of the fuel-system components supply
service manuals; if you can borrow these from your school automotive
shop library or from a service shop, you will find them of great help. Be
sure to write down in your notebook important facts you run across in
the shop or when reading the manuals. This helps you remember the facts
and also gives you a permanent record to which you can refer in case
your memory gets hazy.
\
\'
\ \
[66]
\,
\
\,
\
\
4: Carburetor fundamentals
THIS CHAPTER discusses carburetor fundamentals and describes
the various circuits, or devices, in the carburetor which provide the
proper air-fuel ratios for various operation conditions. The simple
carburetor described in Chap. 3, "Fuel-System Operation," consisting of a venturi in an air horn, a fuel nozzle, and a throttle
valve, could not supply the proper proportions of fuel for the wide
variety of operating conditions typical of the automotive engine.
For instance, during starting and initial warm-up, a rich mixture is
required (high proportion of fuel). At operating temperatures and
intermediate speeds, the mixture must be relatively lean (lower
proportion of fuel). But when the engine is accelerated, or full
power is demanded, then the mixture must be enriched.
§S2. Air-fuel ratio requirements As we have said, the fuel system
must vary the air-fuel ratio with different operating conditions. The
mixture must be rich (high proportion of fuel) for starting and for
idle, but must be relatively lean during part-throttle, intermediatespeed operation. Figure 4-1 is a graph showing typical air-fuel ratios
as related to various car speeds. The car speeds at which these differing ratios are obtained vary with different cars. In the exampk
shown, a rich mixture of about 9:1 (9 pounds of air for each pouna
of fuel) is supplied for initial starting. Then, during idle, the mixture leans out to about 12:1. At intermediate speeds, with the
throttle partly opened, the mixture further leans out to about 15: 1.
But at higher speeds, with the throttle wide open, the mixture is
enriched to about 13:1. Whenever the throttle is opened to accelerate the car, the mixture is momentarily enriched. This is accomplished by an accelerator pump in the carburetor which supplies
additional fuel when the accelerator is moved toward the open
pOSition. Two examples of the enriching effect are shown (in dotted
line) in Fig. 4-1. The first is at a little below 20 mph (miles per
[67]
§53
Automotive Fuel, Lubricating, and Cooling Systems
hour), when the driver opens the throttle to increase car speed.
The second is at a speed of around 30 mph, when the car driver
accelerates but does not keep the throttle wide open. Following
sections describe the various parts of the carburetor that provide
the different air-fuel ratios during car operation.
5!f
I
~Stor
IV
/7 Acceleration
ldle
!( \
"
I
I
I'. \\
1
20!1
o
20
Full tlro/~
I
,I
I
I I
\
\
\
/'
,
\T' ,", '"
40
60
80
100
Cor speed, mph
FIG. 4-l. Graph of air-fuel ratios for different car speeds. The graph is typical
only; car speeds at which the various ratios are obtained may vary with different
cars. Also, there may be some variation in the ratios.
§53.
The various passages in the carburetor
through which fuel and air are fed are called circuits. Different circuits supply fuel during idle, part throttle, full throttle, and so on.
These various circuits work together, or separately during certain
operating conditions, to supply the required air-fuel ratio. Circuits
and mechanisms in the carburetor include
1.
2.
3.
4.
5.
6.
Carburetor circuits
Float circuit
Idling-and-low-speed circuit
High-speed, part-load circuit
High-speed, full-power-circuit
Accelerator-pump circuit
Choke
\
\
These ar~
discussed in detail on following pages.
\
§54.
Float ci~ut
~,
We have already discussed the function of the
float bowl, H<;>at, and needle valve (§4~).
Figure 3-21 shows a
sectional view of a float circuit. When the fuel level in the float
bowl drops, the float also drops, allOWing the needle valve to move
H68]
Carburetor Fundamentals
§55
off the valve seat. This action allows the fuel pump to deliver additional fuel to the float bowl. As the fuel level rises, the float also
rises. This lifts the needle valve up into the valve seat, shutting off
the fuel flow into the float bowl. In actual operation, the float and
needle valve move very little. They tend to take a position where
the valve admits just enough fuel to balance fuel outgo.
§55. Concentric float bowls Many late-model carburetors have a
"wrap-around" type of float bowl instead of having the float bowl
located on one side of the carburetor air horn. The "wrap-around"
FIG. 4-2. Cutaway view of a carburetor with a "wrap-around" float bowl and
dual-float assembly. (Buick Motor Divivion of General Motors Corporation)
float bowl partly or completely encircles the air horn, and a dualfloat assembly is used, that is, one with two floats instead of one.
Figure 4-2 is a cutaway view of a carburetor using this type of
float assembly. Only one float is shown, the other float being located
on the other side of the air horn. The two floats, fastened to the two
ends of a U-shaped lever, work together to operate a Single needle
valve. The needle valve controls fuel delivery to the float bowl, as
in other carburetors. Figure 4-3 shows a similar carburetor partly
disassembled. In this view, both floats of the dual-float assembly
can be seen. One of the advantages claimed for this type of float[69]
Automotive Fuel, Lubricating, and Cooling Systems
§S6
bowl system is that it assures more uniform delivery of fuel to the
engine. That is, even though the carburetor is tilted sharply one
way or another (as it might be with the car on a bank or slope),
the fuel level remains at the proper height with respect to the fuel
nozzle. The fuel nozzle is close to the center of the float bowl;
regardless of how the carburetor is tilted, the fuel level will stand
FLOAT ASSEMBLY
-."_~
___
lOW SPEED JETS ->~!f"r
FIG. 4-3. Dual carburetor (two-barrel) partly disassembled so that the dualfloat assembly can be seen. (Chrysler Sales Division of Chrysler Corporation)
at about the same height in the fuel nozzle. It is also suggested that
the two floats tend to prevent flooding. When the carburetor is tilted
the lower float bowl can act to close the needle valve even though
the upper float is not supported by the fuel at all.
Four-barrel carburetors (§90) are, in effect,
two separate carburetors in a single assembly. One is a primary
carburetor with the job of supplying air-fuel mixture under all operating conditions. The other is a secondary carburetor and has the
job of supplying air-fuel mixture only at special times, as during
high-speed, full-power operation. Each carburetor assembly has its
own float-bowl circuit, consisting of a dual-float assembly, float
§S6. Dual-float circuits
[70)
\,
CarbUf'etor Fundamentals
§57
bowl, and needle valve (Fig. 4-4). The fuel inlet from the fuel
pump is located above the needle valve for the secondary carburetor float bowl. There is a fuel passage to the primary carburetor
float bowl; this bowl has its own needle valve and float assembly.
Note that the two float bowls are separated by a partition. However, there is a balance passage that connects between the two float
bowls which assures equal fuel levels and air pressures in the two
:£loa t bowIs.
Air horn removed ond
ttlrned upside dfJwn to
show floot ossemblies.
Goge is for. cfleckitig
float odjustment,
FIG. 4-4. Float system of four-barrel carburetor. (Oldsmobile Division of General Motors Corporation)
The primary Boat bowl supplies fuel to the two barrels of the
primary carburetor. The secondary float bowl supplies fuel to the
two barrels of the secondary carburetor. Section 90 covers fourbarrel carburetors in detail.
§57. Float-bowl vents The float bowls of many carburetors are
vented into the carburetor au' hom at a point above the choke
valves. The carburetor shown in Fig. 4-4 has the bowls vented in
this manner. The purpose of this arrangement is to equalize the
effect of a" clogged air cleaner. To explain the advantage of this,
let us first recall what we said in our discussion of carburetor fundamentals (§47) about the way atmospheric pressure acts through
a vent in the float-bowl cover. When there is a vacuum in the
venturi (at tip of fuel nozzle), atmospheric pressure pushes fuel
from the float bowl up through the fuel nozzle and out into the
[71]
§58
Automotive Fuel, Lubricating, and Cooling Systems
passing air stream. However, with this system of venting the float
bowl to the atmosphere, clogging of the air cleaner can change the
air-fuel ratio delivered by the carburetor. Here's the reason for that.
If the air cleaner becomes clogged (as it does when it is not
periodically cleaned), it restricts the passage of air into the carburetor air horn. When this happens, a partial vacuum is created in
the air horn. This adds to and increases the vacuum at the fuel
nozzle. As a result, the fuel nozzle will discharge more fuel. This
may make the air-fuel mixture too rich.
But if the float bowl is vented into the upper air horn as shown
in Fig. 4-4, there will be a balance between the float bowl and the
air horn, and the air pressure in the air horn will be the same as in
the float bowl. The effect of a clogged air cleaner is eliminated.
Only the vacuum produced by the air passing through the venturi
will cause the fuel to discharge from the fuel nozzle. There can be
no unbalance between the air horn and the float bowl that would
tend to cause the fuel nozzle to discharge fuel. A carburetor using
this type of venting (venting the float bowl into the air horn) is
called a balanced carburetor. A carburetor in which the float bowl
is vented to the atmosphere is called an unbalanced carburetor.
§58. Idling-and-Iow-speed circuits When the throttle is closed or
slightly open, only a small amount of air can pass through the air
horn and flow around the throttle valve. The air speed is so low,
and there is such a small amount of air passing through, that practically no vacuum develops in the venturi. This means that the
fuel nozzle (centered in the venturi) will not feed any fuel during
operation with a closed or only slightly opened throttle. For this
reason, the carburetor must have another circuit to furnish air-fuel
mixture during this type of operation. The idling-and-Iow-speed
circuit does this job (Figs. 4-5 to 4-8).
The idling-and-Iow-speed circuit consists of a series of openings
through which air and fuel can flow. With the throttle valve closed
as shown in Fig. 4-5 and the engine idling, very little air can pass
between the throttle valve and the air-horn wall, although some
air does get through. Thus, a relatively high vacuum exists on the
engine (or lower) side of the throttle valve. There is a small passage from'Jhe upper part of the air horn through the carburetor'
body to ijle idle adjustment screw. This passage is called the idling[72]
Carburetor Fundamentals
§58
and-law-speed passage. Atmospheric pressure (in upper air hom )
forces air through this passage (as shown by the lines in Fig. 4-5).
Fuel also feeds into this passage from the float bowl as shown by
the arrows. Atmospheric pressure causes this fuel flow; the fuel is
pushed toward the vacuum below the throttle valve. The air and
fuel mix as they move through the circuit toward the idle adjustment screw. The mixture is rich (has a high proportion of fuel).
FIG. 4-5. Idle-and-Iow-speed circuit in carburetor. Throttle valve is fully closed,
and all gasoline is being fed past the idle adjustment screw. Lines indicate air;
arrows indicate gasoline. (Che'OTolet Motor Division of General Motors
Corporation)
It flows past the tapered point of the idle adjustment screw and
down into the intake manifold. It mixes with the small amount of
air that gets past the throttle valve to form a slightly leaner, but
still satisfactorily rich, mixture. The mixture richness can be adjusted by turning the adjustment screw in or out. When it is turned
in, less air-fuel mixhue can pass through the circuit and the final
mixture is leaner. When it is turned out, more air-fuel mixture can
pass through and the final mixture is richer. Adjustment must be
made so that the engine will be supplied with a correctly proportioned mixture for smooth idling.
[73]
Automotive Fuel, Lubricating, and Cooling Systems
§59
§59. Low-speed operation When the throttle is opened slightly, as
shown in Fig. 4-6, the edge of the valve moves past the low-speed
port in the side of the carburetor air horn. This port is usually a
vertical slot or a series of small holes one above the other. With the
throttle valve only slightly opened, it is still impossible for sufficient
air to pass through to produce a vacuum in tlle venturi. As a result,
the main fuel nozzle still does not feed fuel. However, more fuel
4-6. Idle-and-low-speed circuit in carburetor. Throttle valve is slightly
opened, and gasoline is being fed through low-speed port. Lines indicate air;
arrows indicate gasoline. (Chevrolet Motor Division of General Motors Corporation)
FIG.
is needed than can be supplied through the idle port (past the idle
adjustment screw). The low-speed port supplies this additional
fuel. As the edge of the throttle valve moves past the low-speed
port, intake-manifold vacuum is applied to the port. Now, atmospheric pressure (pushing toward the vacuum) causes this port, as
well as the idle port, to start discharging air-fuel mixture. This
mixture is rich, but it is leaned out by the air passing the throttle
valve. A satisfactory mixture is thus supplied for the operating condition. 'As the throttle is opened more, a larger part of the slotted
port (or "more of the drilled holes) is cleared and more air-fuel
mixture is delivered.
[74]
\
Carburetor Fundamentals
§60
§60. Other idJe-and-Jow-speed circuits Figures 4-7 and 4-8 illustrate idle-and-Iow-speed circuits that are somewhat different from
the circuit described above. Both, however, work in a similar manner. In Fig. 4-7, the fuel flows from the float bowl through the main
metering jet and up tlll'ough the idle tube. The idle tube has an
opening of the proper size to allow the correct amount of fuel to
pass through. As the fuel leaves the idle tube, it mixes with air
entering through an air bleed (from the upper au' horn). The mix-
LOW-SPEED PORT
IOLE I'O«T
FIG.
4-7. Idle-and-lowspeed circuit in carburetor. (Studebaker-Packard Corporation)
FIG . 4-8. Carburetor partly cut away so that
idle-and-low-speed circuit of one barrel can be
seen. Fuel flow is shown by alTOws. Carburetor
shown is a dual, or two-barrel unit. (Buick
Motor Division of General Motors Corporation)
ture passes down around the idle-passage wire to the discharge
ports. A secondary au' bleed feeds additional au' to the mixture just
before it reaches the discharge ports. The two discharge ports work
in the same way as those described above. That is, the lower port
discharges air-fuel mixture during idle. Then, when the throttle is
opened slightly, it moves past the upper, or low-speed, port so that
it also begins to discharge air-fuel mixture.
The lower, secondary air bleed (Fig. 4-7) has another function
aside from bleeding air into the air-fuel mixture as it moves down
the idle passage. At higher engine speeds, when the throttle is
opened and the idle system is inoperative, the air bleed discharges
[75]
§60
Automotive Fuel, Lubricating, and Cooling Systems
a small quantity of fuel into the air stream going through the air
horn. In other words, at higher speeds it works in reverse. Instead
of bleeding air into the idle passage, it feeds fuel into the air horn.
The fact that the air-bleed nozzle projects slightly into the air horn
causes this latter action. The amount of air-fuel mixture fed into the
air horn is small. But it is sufficient to keep the idle passage filled
at all times. Then, when the throttle is suddenly closed, the idle
circuit can take over instantly without the hesitation that might
occur if the idle passage were not filled.
Figure 4-8 is a partial cutaway view of a dual, or two-barrel, carburetor. This type of carburetor, often used on eight-cylinder engines, has two separate air horns; each air horn supplies air-fuel
mixture to four cylinders (§89). In the illustration, one of the air
horns has been partly cut away so that the idle-and-Iow-speed
circuit can be seen. The fuel flows from the float bowl through the
metering-rod jet and the passage leading to the main nozzle. It then
passes upward through the low-speed jet which is of the correct
size to feed the proper amount of fuel. As it leaves the jet, it mixes
with air entering the idle passage through a bypass. The mixture
passes through an economizer, or drilled passage and then combines
with additional air entering through an air bleed. This additional
air tends to break the fuel into still finer particles, or to atomize
it more completely. The air-fuel mixture then moves down the idle
passage to the idle and 10'Y-speed ports. During idle, it feeds out
past the idle adjustment screw in the lower port. When the throttle
is opened slightly, it moves past the upper (or low-speed) port. The
low-speed port then begins to feed air-fuel mixture into the air
horn.
At higher speeds, the high-speed circuit takes over, and fuel
begins to feed into the air horn from the main nozzle. As this happens, the vacuums at the idle and low-speed ports drop so low that
they fade out; the high-speed circuit takes over completely.
A somewhat different type of idle circuit is shown in Fig. 5-14.
In this carburetor the idle adjustment screw works in reverse from
those previously discussed. In the unit shown in Fig. 5-14 the idle
adjustment screw allows air to bleed into the idle circuit. Thus,
as the idle adjustment screw is backed out, it will admit more air
into the idle circuit, and the air-fuel mixture will be leaner. But when
the idle adjustment screw is turned in, less air will be admitted into
[76]
\
Carburetor Fundamentals
§61
the idle circuit, and a richer mixture will be discharged from the
idle port. The unit shown in Fig. 5-14 is an "updraft" carburetor
(discussed in §87). However, this idle-adjustment-screw arrangement is used on both updraft and downdraft carburetors, as explained in §87.
NOTE: On many engines the ignition distributor has an advance
mechanism which advances the spark under part-throttle conditions
(see §82). With this system, the distributor is connected to the
carburetor through a vacuum line (see Fig. 5-1). The vacuum line
opens into holes or a slot cut in the carburetor air horn, approximately on a level with the low-speed port. The two openings
(vacuum and low-speed port) should not be confused. For further
information on vacuum-advance mechanisms in ignition distributors, refer to Automotive Electrical Equipment, another of the
books in the McGraw-Hill Automotive Mechanics Series.
§61. High-speed, part-load circuit When the throttle valve is
opened sufficiently so the edge moves well past the low-speed port,
the difference in vacuum between the upper part of the air horn
and the low-speed port becomes very small. It is too small to cause
any amount of air-fuel mixture to discharge from the low-speed
port. However, under this condition, sufficient air is moving through
the air horn to cause the high-speed circuit to function. The highspeed circuit includes the fuel nozzle (called the main nozzle or
high-speed nozzle), the venturi, and the fuel passages from the float
bowl to the nozzle (see Fig. 4-9). The partial vacuum in the venturi, produced by the air movement through it, causes the nozzle to
discharge fuel into the air. This action is described in detail in §47.
The air-fuel mixture produced is of the correct proportions to meet
the intermediate throttle, part-load operating requirements. The
main nozzle supplies the fuel during operation with the throttle
valve partly to fully opened.
Actually, the low-speed circuit does not suddenly stop supplying
air-fuel mixture, nor does the high-speed circuit suddenly begin to
supply fuel when the throttle valve is slowly opened. The delivery
of air-fuel mixture from the low-speed circuit gradually tapers off as
the edge of the throttle valve swings past the low-speed port.
During this interval the increasing flow of air through the air horn
and the venturi sets the high-speed circuit into operation. Thus, the
£77]
Automotive Fuel, Lubricating, and Cooling Systems
§62
high-speed circuit gradually takes over as the low-speed circuit
fades out. These two circuits are so carefully balanced that, as the
throttle is gradually opened, a nearly constant air-fuel ratio is maintained during the shift from the low-speed to the high-speed circuit.
As engine speed increases, larger amounts of air pass through the
air hom and venturi. This produces a greater vacuum in the venturi
Throttle volve
FIG. 4-9. High-speed circuit in carburetor. Throttle valve is fairly well open,
and gasoline is being fed through high-speed nozzle. Lines indicate air; arrows
indicate gasoline. (Chevrolet Motor Division of General Motors Corporation)
which, in turn, causes the main nozzle to discharge greater amounts
of fuel. Thus a nearly constant air-fuel ratio is maintained by the
high-speed circuit.
To aSSure mOre perfect mixing of the fuel
and air, carburetors usually have multiple venturi, one inside another. An example of a triple-venturi carburetor is shown in Fig.
5-8. The upper, or primary, venturi produces the vacuum that causes
the main nozzle to discharge fuel. The secondary venturi passes a
blanket of air, which holds the spraying fuel away from the walls of
the air horn, where it might otherwise condense. At the same time,
turbulence between the central stream of air-fuel mixture and the
outer blanket of air causes better mixing and finer atomization. of
the fuel spray. This same action is repeated in the main venturi.
[78]
§62. Multiple venturi
\
Carburetor Fundamentals
§6'3
§63. Other high-speed circuits Figures 4-10 and 4-11 illustrate other
types of high-speed circuits in carburetors. Even though the various
carburetors are somewhat different in appearance, design, and construction, they all function as explained in previous paragraphs;
that is, the high-speed circuit takes over at some intermediate
throttle opening as the low-speed cu.-cuit fades out. In the circuit
FIG. 4-10. High-speed circuit in carburetor. (Studebaker-Packard Corporation)
FIG. 4-U. Carburetor partly cut away
so that high-speed circuit of one barrel
can be seen. Fuel flow is shown by arrows . The carburetor is a dual, or twobarrel, unit. (Buick Motor Division of
General Motors Corporation )
shown in Fig. 4-10 tlle high-speed bleeder allows air to be drawn
into the main discharge jet where it mixes with the fuel. This causes
a mixture of air and fuel to be discharged from the fuel nozzle;
better atomization and vaporization of the fuel is thereby achieved.
If any vapor bubbles form in the hot fuel as it moves up the main
discharge jet, they follow the outside channel around the jet and
collect in the high-speed bleeder dome. From there, the vapor
bubbles are drawn down into the jet again, along with the bleeding
air. This design assures more uniform dehvery of fuel even during
exceptionally hot operation.
[79]
§64
Automotive Fuel, Lubricating, and Cooling Systems
The carburetor shown in partial cutaway view in Fig. 4-11 is a
dual, or two-barrel, carburetor such as described in §60 and illustrated in Fig. 4-8. In operation, the high-speed circuit draws fuel
from the float bowl, past the metering-rod jet, up the main nozzle
passage, and out through the main nozzle. Fuel vapor bubbles that
might form in the main nozzle passage rise through the low-speed
jet passage and then exhaust through the antipercolator passage
into the main nozzle. This assures uniform delivery of fuel even
though extreme heat might be causing fuel vapor bubbles to form.
§64. High-speed, full-power circuit The air-fuel ratio provided by
the high-speed circuit is satisfactory for all engine operation from
partly opened to nearly wide-open throttle. However, at wide-open
throttle, where full engine power is desired, an increase in mixture
richness is required. To obt ain this increased richness, and thus full
engine power, an additional device is incorporated in the carburetor. This device admits an additional flow of fuel to the main
nozzle so that it discharges more fuel. Two general types of device
are in use-one mechanically operated,
METERING
the other operated by intake-manifold
ROD
vacuum.
§65. Mechanically operated full-power
circuit The mechanically operated device makes use of a metering-rod jet and
a metering rod with two or more steps
of different diameters as shown in Fig.
4-12. The metering rod is connected to
the throttle linkage, or connector rod, as
shown in Fig. 5-8. When the throttle is
opened, the throttle connector rod moves
FIG . 4-12. Metering rod and
so that the metering rod is raised. At
metering-rod jet for securing added performance at intermediate throttle, the larger diameter,
or step, is in position in the metering-rod
full throttle.
jet. This somewhat restricts the flow of
fuel to the main nozzle. Sufficient fuel does flow, however, to provide the proper air-fuel ratio during intermediate throttle operation.
But when the throttle is fully op ened, the metering rod is raised
enough to cause the smaller diameter, or step, to be lifted up into
the meterin&rod jet. The jet is therefore less restricted and a larger
[80]
•
\.
§66
Carbu'retor Fundamentals
quantity of fuel can pass through it. The fuel nozzle therefore feeds
more fuel and a richer mixture results.
In the carburetor shown in Fig. 4-11 the metering rod has three
diameters, or steps. In this unit, the largest, or economy, step is in
place in the metering-rod jet in the lower-speed ranges. However,
when the throttle is partly opened for higher speed or acceleration,
the metering rod is raised so that the middle step clears the jet.
More fuel can therefore pass tlu·ough the jet for satisfactory performance in the intermediate-speed range. When the throttle is
fully opened, the metering rod is fully raised so that the smallest
step is in the jet; this permits additional fuel delivery through the
jet for full-power, high-speed performance.
§66. Vacuum-operated full-power circuit The full-power, fullthrottle device may also be operated by intake-manifold vacuum,
as shown in Fig. 4-13. The design illustrated makes use of a valve
H-~3!P
IST
ON
SPRING
FIG. 4-13. Vacuum-operated, full-power circuit in carburetor. (StudebakerPackard Corporation)
in the power, or bypass, jet. The valve is held in place in the bypass
jet by a small spring during part-throttle operation. In this position
no fuel can How through the bypass jet; all fuel is fed to the main
nozzle through the main metering jet. Above the valve is a vacuum
piston (or power piston). The upper chamber above the power
[81]
Automotive Fuel, Lubricating, and Cooling Systems
§67
piston is 'connected through a vacuum channel to an opening just
below the throttle valve. Under part-throttle operation, the vacumn
in the intake manifold (or just below the throttle valve) is sufficient
to hold the power piston up against the piston-spring tension. But
when the throttle is opened wide, intake-manifold vacuum drops.
The vacuum is then insufficient to hold the power piston. Now,
spring pressure forces the piston down. The rod below the piston is
also forced down, and the end of the rod moves down against the
valve, causing it to open. Additional fuel can now be fed into the
main nozzle through the bypass jet and bypass passage. This enriches the mixture for wide-open-throttle, full-power operation.
§67. Combination mechanically operated and vacuum-operated fullpower circuit Some carburetors use a full-power circuit that has a
combination device operating on both mechanical movement and
intake-manifold vacuum (Figs. 4-11 and 4-14). On such applica-
FIG. 4-14. Combination mechanically operated and vacuum-operated full-power
circuit. Both vacuum-piston and throttle positions control position of metering
rod. A, nozzle; B, retainer plug; C, plug; D, metering rod; E, linkage; F,
metering-rod jet; G, vacuum piston; H, spring; J, linkage to throttle. (American
Motors Corporation)
[82]
,
\,
\
Carburetor Fundamentals
§67
tions a metering rod is used, as described above. It is linked to the
throttle so that wide-open throttle causes the smaller diameter of
the metering rod to clear the metering-rod jet and feed additional
fuel to the main nozzle. The metering rod is also linked to a vacuum
piston which is assembled into a chamber in the carburetor. When
the throttle is only partly opened and a vacuum is present in the
intake manifold, the vacuum piston is held down in the chamber.
However, when intake-manifold vacuum drops, regardless of throttle
opening, the vacuum piston is pushed up by the piston spring. This
movement is carried by a link to the metering rod, raising it. Now,
more fuel is fed to the main nozzle, and a richer mixture results to
provide full-power performance. When vacuum increases in the
intake manifold, the vacuum piston is again pulled down so that
the larger diameter of the metering rod enters the jet. This restricts
the fuel flow, resulting in a leaner mixture. The metering rod is thus
controlled by both intake-manifold vacuum and throttle position.
CHECK YOUR PROGRESS
Progress Quiz 1
This is the first progress quiz you have seen in this book, although you
have already come across the chapter checkups. This chapter is longer
than previous chapters, however, and thus it is a good idea for you to
pause before you have finished the chapter to check your progress. This
quiz and the chapter checkups have been put into the book to help you.
They help you in two ways. First, they show you how well you are remembering the important points in the material you are reading. Secondly, they provide a review of the important points which helps fix
them more firmly in your mind. If any of the questions seem hard to
answer, reread the pages that will give you the answer.
Completing the Sentences
The sentences below are incomplete. After each sentence there are
several words or phrases, only one of which will correctly complete the
sentence. Write each sentence down in your notebook, selecting the
proper word or phrase to complete it correctly.
1. According to the graph of air-fuel ratios for different operating conditions, the ratio during engine idle is about
9:1
12:1
13:1
15:1
2. According to the graph of air-fuel ratios for different operating con[83)
§68
Automotive Fuel, Lubricating, and Cooling Systems
ditions, the ratio during intermediate speed, part-throttle operation
9:1
12:1
13:1
15:1
is about
dual-float assembly
3. Concentric-type Roat bowls contain a
balance vent
four-barrel setup
4. Float bowls may be vented in two ways; when vented into the air
horn, the carburetor is
a balanced carburetor
an un-
5.
6.
7.
8.
balanced carburetor
a four-barrel carburetor
a dual carburetor
When the throttle is closed and the engine is idling, the air-fuel mixture Haws
around the throttle valve
past the idle ad;ustment screw
past the main nozzle
During low-speed operation, when the throttle is only slightly open,
most of the fuel supplied to the engine is discharged through the
idle port
low-speed port
main nozzle
venturi
During high-speed operation, when the throttle is wide open, the fuel
supplied to the engine is discharged through the
idle port
low-speed port
main nozzle
The full-power circuit may be operated mechanically or by
metering rod
intake-manifold vacuum
linkage to throttle
§68. Accelerator-pump circuit When the throttle is suddenly moved
from a closed to an open position, a momentary out-of-balance
condition results in the carburetor. For acceleration, the engine
requires a relatively rich mixture; the sudden power demand means
that the engine must have additional fuel richness. However, when
the throttle is opened, the effect is to "dump" air into the intake
manifold, thus suddenly reducing manifold vacuum. The sudden
change in air flow, plus the need for a momentary richness, means
that the main nozzle will not feed adequate fuel for acceleration.
To carry the carburetor over this momentary lapse, which could
cause a "flat spot" in engine performance (or logy acceleration), an
acceleration-pump circuit is included in the carburetor.
Figure 4-15 shows a typical accelerator-pump circuit. It contains
a pump assembled into the float bowl with a fuel passage up to a jet
at one side of the air horn. The pump piston is linked to the throttle
so that when the throttle is opened, the piston is pushed down. This
downward movement forces fuel from the pump cylinder under the
piston. The fuel moves through the fuel passage and out the pump
jet into the air stream passing through the air-horn. This momentarily
enriches the mixture and causes the engine to pick up speed quickly;
quick, powerful acceleration results. A small check valve in the fuel
[84]
Carburetor Fundamentals
§69
Accelerating pump lever __ -....
4-15. Accelerator-pump system in carburetor. When the piston moves down,
fuel is sprayed from the pump jet as shown by the arrows. (Chevrolet Motor
Division of General Motors Corporation)
FIG.
passage prevents fuel from being delivered to the air horn as a result of air velocity in the air horn. Fuel is delivered only when the
throttle is opened and the accelerator-pump piston is forced downward.
§69. Other accelerator-pump circuits Figure 4-16 is a sectional view
of a carburetor with an accelerator-pump circuit similar to the one
described. Figure 4-17 shows a somewhat different acceleratorpump circuit used in a dual carburetor. This circuit contains two
discharge nozzles, one for each carburetor air horn. Thus, in this
carburetor the fuel from the accelerator-pump piston movement is
split into two sprays, one for each air horn. All the various
accelerator-pump circuits work in a similar manner. When the
throttle is opened, the pump piston is forced downward and fuel is
discharged into the air horn (or air horns). When the throttle is
closed, the pump piston is pulled upward so that the pump chamber
becomes re£l1ed with fuel, ready for the next acceleration period.
Most of the pistons are spring-loaded with a "duration" spring (see
[851
Automotive Fuel, Lubricating, and Cooling Systems
§69
PUMP JET
PUMP QUTLET
NEEDLE
~r
fIG. 4-16. Sectional view of carburetor showing accelerator-pump system.
(Oldsmobile Division of General Motors Corporation)
RETAINER
SPRING
DURATION
SPRING
OUTLET
INLET BALL
CHECK
\
4-17. Accelerator-pump system and location of discharge nozzles in a dual
carbureto'\'. (Studebaker-Packard Corporation)
FIG.
[86]
\
Carburetor Fundamentals
§71
Fig. 4-17). That is, the piston is not actuated directly by the throttle
linkage, but through the spring. The throttle linkage actually compresses the spring, spring-loading the piston. Then the piston is
moved by the spring to produce the fuel discharge. The purpose of
the spring is to prevent excessive pressures in the pump and to give
some duration (or length of time) to the fuel spray. This guards
against a sudden momentary "squirt" of fuel and provides a more
even enrichening effect that lasts for several seconds, or for as long
as the spring continues to move the piston.
§70. Combination accelerator pump and full-power valve Some carburetors have the full-power valve so arranged that it is operated
by the accelerator pump. With this arrangement, full-throttle position of the accelerator-pump piston forces the full-power valve off
its seat so that additional fuel is delivered from the main nozzle.
The valve operates as described in §§66 and 67. The only difference
is that it is operated by the pump piston instead of by a vacuum
piston or other throttle linkage.
§71. Choke When the engine is being cranked for starting, a very
rich mixture must be delivered to the cylinders. Since normal cranking speeds may be below 100 rpm (revolutions per minute), air
speeds through the carburetor are low. In addition, with a cold
engine, the gasoline will not evaporate readily. Consequently, more
than the normal amount of fuel must be delivered to the air stream
passing through the air horn. The choke causes this fuel-delivery
increase. The choke consists of a butterfly valve in the top of the
air horn (Fig. 4-18). The valve is a round disk that can be tilted
more or less in the air horn to choke off the air flow into the air horn
more or less. It may be operated mechanically, thermostatically, by
vacuum, or electricity. When the choke is closed (in position shown
in Fig. 4-18) only a small amount of air can get past it. Thus, when
the engine is being cranked with the choke closed, a fairly high
vacuum is created in the air horn, causing the main fuel nozzle to
discharge a heavy stream of fuel. The quantity delivered is sufficient
to produce the very rich mixture needed for starting the engine.
The choke valve is not connected rigidly to the choke control, but
is connected through a spring. The spring is strong enough to hold
the choke closed during cranking. But when the engine start5, the
sudden increase in vacuum (as engine speed increases to several
[87]
Automotive Fuel, Lubricating, and Cooling Systems
§72
hundred revolutions per minute) causes the choke valve to be partly
opened (by atmospheric pressure above it). This admits more air
and somewhat leans out the mixture for engine operation during the
warm-up period. The choke valve may be unbalanced by being
FIG. 4-18. Operation of choke when starting engine. (Chevrolet Motor Division
of General Motors Corporation)
mounted off center on the choke-valve shaft (as shown in Fig.
4-18), or there may be a small spring-loaded section in the valve,
which opens when the vacuum increases after the engine starts.
§72. Automatic chokes Mechanically controlled chokes are operated through a pull rod on the dash in the driving compartment.
The pull rod is linked to the choke valve in the carburetor air hom,
causing the choke valve to close when the rod is pulled out. A
spring connection is incorporated at the choke valve so that the
choke valve can spring partly open when the engine starts. The
driver must remember to push the choke control back when the
engine is warmed up. If he fails to do this, the engine will be
supplied with an overrich mixture that will result in fouling of spark
plugs and formation of carbon in the cylinders. To prevent such
[88]
,I
I
\
Carburetor Fundamentals
§72
conditions, many carbmetors now have automatic devices that close
the choke valve when the engine is cold and gradually open it as
the engine warms up. The automatic-choke devices are all similar,
although they vary in detail. They operate on exhaust-manifold
temperature and intake-manifold vacuum (Figs. 4-19 to 4-25).
In the typical automatic choke shown schematically in Fig. 4-19
a spiral bimetal-thermostat spring and a vacuum piston are linked
together to the choke valve and control its position. The bimetalthermostat spring is made up of two different metal strips welded
FIG. 4-19. Automatic choke shown schematically. Thermostatic spring and
vacuum piston operate together to determine amount of choke-valve opening.
together and formed into a spiral. The two metals expand at different rates as the thermostat is heated, and this causes the spring
to wind up. The spring unwinds when it cools. When the engine is
cold, the spring has unwound enough to close the choke valve, and
it spring-loads the choke valve in the closed position. When the
engine is cranked, a rich mixtme is delivered to the cylinders, and
the engine starts. If the choke valve now remained completely
closed, the mixtme would be too rich even for initial running. On
some applications a spring-loaded section of the choke valve is
pulled downward by the vacuum in the air horn to permit additional air to pass so that the mixtme is leaned out to some extent.
Other choke valves are llilbalanced (choke-valve rod on one side)
so that the vacuum in the air horn causes the valve partly to open
[89]
Automotive Fuel, Lub1'icating, and Cooling Systems
§72
against: ~- the
thermostatic spring tension. The vacuum affects the
vacuum piston in the choke also, causing it to move down against
the thermostatic spring tension so that some additional opening of
the choke valve is obtained. The carburetor thus supplies a mixture
of the proper richness for operation during initial, cold-engine
operation.
sA
THERMOSTAT-HOUSING
y
,
. THERMOSTAT HOUSING
AND COIL ASSEMBLY
FIG. 4-20. Carter climate-conb'ol automatic choke. The vacuum-choke piston is
connected through a vacuum channel to the intake manifold, while the thermostat housing receives heat through a hot-air passage from the exhaust manifold.
(Oldsmobile Division of General Motors Corporation)
When the throttle is opened, the mixture must be enriched. The
action of the accelerator pump (§68 ) does enrich the mixture
momentarily, but additional richness is required, since the engine
is cold. lIhis added richness is secured by the action of the vacuum
piston in the automatic choke. The opening of the throttle valve
[90]
\
Carburetor Fundamentals
§72
~
FIG. 4-21. Disassembled view of an automatic choke. Thermostatic spring is in
the housing to right. (Studebaker-Packard Corporation)
1. Choke valve screws
5. Choke-valve shaft
11. Retainer clip
2. Choke valve
and lever
12. Screw
6. Choke piston
13. Climatic-control
3. Air horn and
housing with
7. Choke trip lever
climatic-control
8. Baffle plate
thermostat
housing
4. Fast-idle cam
9. Baffie-plate screw
14. Fast-idle link
10. Gasket
" PASSAGES
FIG. 4-22. Carburetor cut away so the automatic-choke construction can be
seen. (Bu,ick Motor Division of General Motors Corporation)
i 91 ]
Automotive Fuel, Lubricating, and Cooling Systems
§72
causes a loss of vacuum in the intake manifold. This releases the
vacuum piston so that it is pulled upward by the thermostatic
spring tension. This movement is transmitted to the choke valve,
causing it to move toward the closed position an amount depending
on how much vacuum remains in the intake manifold. Dming the
first few seconds of operation the choke valve is thus controlled by
the vacuum piston.
The thermostatic spring begins to take over, however, as the
engine heats up. The thermostatic spring is placed in the carbu-
FIG. 4-23. Stromberg choke control.
This design is much like the one in Fig.
4-20 except for the placement of the
vacuum piston C and choke valve A,
and the manner of linking the vacuum
piston and the thermostatic spring B
together. D is fast-idle cam and E is
idle adjustment screw. ( BUick Moto"
Division of General Motors Corporation)
retor in such a position that it is subjected to engine heat. A small
tube connects the thermostatic-spring housing and the exhaust
manifold. Heat passes through this tube, causing the Spl'ing to heat
up. This heating of the thermostatic spl'ing causes it to wind up.
The winding takes place l'ather slowly as the engine approaches
operating temperatme, taking several minutes when the engine is
stal'ted at low temperatme. As the spring winds up, the spI'ing
tension holding the choke closed is gradually relieved, and the
choke valve begins to open. When operating temperatme is reached,
the choke valve is completely open and, even though vacuum
changes do take place in the intake manifold, the vacuum piston
cannot ca~se
the choke valve to close. During the interval of heating up, the vacuum piston can enrich the mixtme when the throttle
[921
\
\
Carburetor Fundamentals
§72
is opened, as has already been described. As the engine warms up,
the operation of the vacuum piston has less and less effect on the
richness of the mixture until, when operating temperature is
reached, it has no further effect, the thermostatic spring having
wound up enough to spring-load the choke in the open position.
Before the choke can again operate, the engine must be stopped
FIG. 4-24. Stromberg choke control mounted on carburetor. This is the exterior
view of the choke control shown in previous illustration. (Buick Motor Division
of General Motors Corporation)
and allowed to cool. As it cools, the thermostatic spring in the choke.
unwinds, causing the choke valve to close, so that the above
sequence of operations will occur again. These chokes are often
called hot air chokes since they operate when heated air from the
exhaust manifold passes through them. Figures 4-20 to 4-25 illustrate various types of automatic-choke control.
A careful study of the various illustrations of automatic chokes
will disclose that they are basically similar in construction and
[93]
Automotive Fuel, Lub1'icating, and Cooling Systems
§73
operation. The choke shown in Fig. 4-25 is somewhat different,
however, and a further explanation of its action might be desirable.
It operates electrically. When the starting motor is operated (to
crank the engine), the electromagnet in the choke is energized.
This causes the armatUl'e to be pulled upward so that the bimetal
thermostat is pivoted upward. This action, in tum, causes the shaft
in the choke to turn. Since the shaft is linked to the choke valve
(see Fig. 9-3) , turning of the shaft causes the choke valve to move
toward the closed position. Then, after the engine starts and the
BI-METAL
THERMOSTAT
CONTRACTS
AS IT IS WARMED
FIG. 4-25. Construction of elech'ic choke. (Plymouth Division of Chrysler
Corporation)
starting motor is stopped, the electromagnet releases the armature
so that the choke valve partly opens. The position that the choke
valve takes is then determined by how cold the engine is. As the
engine warms up, the bimetal thermostat contracts, further dechoking the engine. When the engine reaches operating temperatUl'es, the choke valve has been opened to the wide-open position.
§73. Manifold heat control As a further means of obtaining smooth
engine operation during warm-up, a manifold heat control is used.
This device causes considerable heat transfer from the exhaust
manifold tQ the intake manifold during initial operation with a cold
engine. Tille heat transfer preheats the air-fuel mixture and assures
[94]
I'
\
\
§73
Carburetor Fundamentals
better fuel vaporization and thus better initial engine operation.
To secure this heat transfer, the intake manifold is placed above the
exhaust manifold, and there is an opening to the jacket that surrounds a part of the intake manifold (Figs. 4-26 and 4-27). Below
this opening there is a thermostatically controlled butterfly valve,
called the manifold heat-control valve.
The thermostat is a coiled spring made of two strips of different
metals welded together. These two metals expand at different rates
GASKET
INTAKE
MANIFOLD
( Ford D ivi-
as temperature increases; this causes the thermostat to wind up.
When the temperature decreases, the thermostat unwinds. This
latter condition causes the butterfly valve to assume the pOSition
shown in Fig. 4-26 when the engine is cold. Thus, when the engine
first starts, the hot exhaust gases circulate through the jacket surrounding the intake manifold, quickly heating the intake manifold
and assuring adequate vaporization of the fuel during the warm-up
period of operation. An end view of this pOSition is shown in the
left-hand illustration in Fig. 4-27.
As soon as the engine begins to heat up, the thennostat, becoming hot, winds up, causing the heat-control valve to rotate into
[95]
Automotive Fuel, Lubricating, and Cooling Systems
§74
the position shown to the right in Fig. 4-27. This shields off the
jacket surrounding the intake manifold, preventing any further flow
of hot exhaust gases through it. Without such a "shutoff" arrangement, too much heat would be introduced into the intake manifold,
FIG. 4-27. The two extreme positions in the exhaust manifold of the manifold
heat-control valve that controls the How of exhaust gases through the intakemanifold jacket. (Chevrolet Motor Division of General Motors Corporation)
prodUCing an excessive expansion of the air-fuel mixture, so that an
insufficient quantity (by weight) would reach the engine cylinders.
§74. V-8 manifold heat control The heat-control arrangement described in the preceding section is for an in-line engine. A different
arrangement is required for a V -8 engine since this type of engine
normally has the intake manifold mounted between the two banks
of cylinders, while there are two exhaust manifolds, One for each
bank, mounted to the outsides of the banks. Thus in the V-8 engine
there is a spec'ial passage in the intake manifold that carries exhaust
gas from qne exhaust manifold to the other (see Fig. 5-19). There is
a therm@statically controlled valve in one exhaust manifold. When
[96]
\
\.
Carburetor Fundamentals
§75
this valve is closed, that exhaust manifold cannot discharge through
its own exhaust pipe. It must discharge through the special passage
in the intake manifold and from there through the exhaust pipe
for the other exhaust manifold. As the exhaust gas is shunted
through this special passage in the intake manifold, it passes under
the carburetor mounting pad (Fig. 4-28). Heat is thus introduced
Hot gases circulate
around intake
manifold passages
.
4-28. Intake manifold and carburetor idle-ports heating passages. Hot exhaust gases heat these areas as soon as the engine starts. (Cadillac Motor Car
Division ot General Motors Corporation)
FIG.
into the intake manifold. Then, when the engine warms up, the
thermostatically controlled valve in the exhaust manifold opens to
permit normal exhaust-gas discharge from both exhaust manifolds
and pipes. The exhaust gases no longer pass through the intakemanifold passage.
§75. Anti-icing When fuel is sprayed into the air passing through
the air horn, it evaporates, or turns to vapor. We have already noted
that this is a change of state (§29) and that during the process, the
fuel takes on heat. In other words, as the fuel vaporizes, it "robs"
the surrounding air and metal parts of heat. This is the same effect
that you get when you pour alcohol on your hand. The alcohol
evaporates, <Crabbing" your hand of heat as it does so. Your hand
feels cold. If you blow on your hand, thus causing the alcohol to
evaporate faster, your hand will feel colder. The faster that evap[971
Automotive Fuel, Lubricating, and Cooling Systems
§76
oration takes heat away from your hand, the cooler your hand will
feel.
In the carburetor the spraying and evaporating fuel takes considerable amounts of heat from the air. This cools the air. In fact,
under certain conditions, the air and surrounding metal parts are
cooled so much that any moisture in the air will condense on the
metal parts and then freeze. The ice that forms can actually cause
the engine to stall. The conditions under which this could happen
include high humidity (air very damp, or having high water-vapor
content) and relatively low air temperature. The cooling, or refrigerating, effect of the evaporating fuel then further reduces the
air temperature so that water condensation and freezing take place.
The ice blocks off the air passages and engine stalling follows.
To prevent this condition, many engines now have special antiicing circuits to heat the carburetor during the engine warm-up
period. After the engine has warmed up, there is little danger of
ice forming. One arrangement for a V-8 engine is shown in Fig.
4-28; a special passage or circuit for hot exhaust gases is incorporated in the carburetor. During the warm-up period, when
hot exhaust gases are being shunted from one exhaust manifold to
the other (as explained in §74), some of the hot exhaust gas passes
around the carburetor idle ports and near the throttle-valve shaft.
This adds enough heat to guard against ice formation. Another
carburetor has water passages in the carburetor. You can see one
of the water passages into the throttle body of the carburetor shown
in Fig. 4-3 (to lower right). The water used is the engine cooling
water; a small amount of the cooling water bypasses through a
special water manifold in the lower part (or throttle body) of the
carburetor. This adds sufficient heat to the carburetor to prevent
icing and consequent stalling of the engine during the warm-up
period.
When the engine is cranked, the throttle
must be partly opened, or cracked, so that enough air can get
through the air horn and to the engine. To crack the throttle during
engine cranking, a special linkage is installed between the crankingmotor-switch lever and the throttle linkage. When the cranking
motor is operated, this special linkage causes the throttle to be
opened a small amount. Figure 4-29 shows one type of linkage with
[98]
§76. Throttle cracker
I
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Carburetor Fundamentals
§77
a special tool installed to check the adjustment. Adjustment must be
correct so that the throttle will be opened the proper amount during
cranking.
Throf//e cross-shuff lever-Ieff .r/Qe,
,,/
Throltle-crcrcker_ -adjusftnq screw /"-1=:r.1001/
J-I469
Bellcrank
/
FIG. 4-29. Linkage connecting cranking-motor-switch lever and accelerator so
that throttle is cracked during cranking. On solenoid-actuated cranking-motorcontrol systems, there is a linkage to the solenoid to perform the same function.
§77. Fast idle When the engine is cold, it is desil'able to maintain
some throttle opening so that the engine will idle faster than it
would when wann. Otherwise, the slow idle, with the engine cold,
might cause the engine to stall. The reason for this is that with the
engine cold, a slow idle does not provide enough air for adequate
fuel delivery and vaporization. But if the engine idles faster, the
additional air passing through provides a much brisker air-fuelmixture movement and better vaporization. To obtain fast idle
with t~e
engine cold, a fast-idle cam linked to the choke valve is
used (Fig. 4-30). The automatic choke (not shown in illustration )
controls the opening of the choke valve. During the warm-up
period, the choke valve is fully or partly closed. In this position,
the linkage to the fast-idle cam holds the cam so that the adjusting
screw rests on the high section of the cam when the throttle is
released. This means that the adjusting screw will not let the throttle
close completely; the throttle is held partly open so that the engine
idles fast. As the engine starts to warm up, the choke valve gradually
opens (due to automatic-choke action). This causes the fast-idle
cam to rotate. By the time the choke is fully opened, the fast-idle
[99}
Automotive Fuel, Lubricating, and Cooling Systems
§78
cam has rotated enough to have moved the high sections away
from under the adjusting screw. Now, when the throttle is released,
the adjusting screw can move into the
low section of the fast~idle
cam, and a
normal slow idle results.
§78. Antipercolator The carbmetor is
placed above the engine and is subject
to engine heat. Under certain conditions, as when idling after a hard run,
heat build-up might be great enough
to cause the high-speed circuit to percolate. TIllS action might be likened
to the action that takes place when a
£lled teakettle is placed on a stove.
As the water in the kettle begins to
FAST
boil, vapor pressme causes water to be
IDLE
forced out thl'Ough the teakettle spout.
CAM
However, the vapor pressure can be
FAST
eliminated
merely by lifting the teaIDLE
ADJUSTING
kettle lid. Similarly, by using a small
SCREW
vent in the high-speed circuit, vapor
FIG. 4-30. Linkage between
choke valve G, fast-idle cam, pressure can be relieved to prevent
and throttle. When the fast- percolation in the circuit and thereby
idle cam is in position shown, prevent boiling of the fuel out of the
fast-idJe adjusting screw does main nozzle. The antipercolating denot allow throttle to close comvice used on some carburetors is conpletely. H, screw; K, clearance. (Buick Motor Division nected into the throttle system so that
of General Motors Corpora- a small valve opens as the throttle is
tion)
released (Fig. 4-31). Another anti~
percolating device consists of a tube connected from the high-speed
circuit to the upper part of the air hom (Fig. 4-11). This tube
relieves vapor pressure sufficiently to prevent percolation.
§79. Air bleed In the high-speed circuits in many carbmetors,
devices are incorporated to permit air to enter, or bleed into, the
high-speed or main nozzle. Some premixing of the fuel with air
is thereby produced, so that the atomization is improved when the
high-speed , circuit is in operation (see Fig. 4-10). In addition, a
better balance of the air~fuelmxt
ratio is maintained, since the
[100]
\,
.
§80
Carburetor Fundamentals
speed and volume of air passing through the air hom (determined
by throttle opening and engine speed ) govern the amount of air
that bleeds into the main nozzle. This combats the tendency for
excessive gasoline to feed through the main nozzle when air speed
through the air hom is high, since considerable air bleeds into the
main nozzle under such a condition. When air speed through the
a,
~
--- ---- -- -- Pump operatinq lever and counters/Jaf'tassembly
----------Pumparm OInd collar assembly
-------Dusl cover
------- Meterinq-rod sprinq
Connecfor link
___ ,' Anlipercolator-cap and rocker-arm assembly
- _ -: ~-,
Plunqerad
rod assembly
_-&O'7 A.._
_ ____ ' Bowl-cover qa6lref
~
------ -Low-speed iel assembly
.Pump discharge relainer pluq assembly
-Pump sprinq
---- Pump check ball
~t'I"
I:>. ' '",~
~f
~
~
__- ,~- - Mefring
rod
Pump drainer
-------- ------ Melerinq-rodjef and qaskefassembly
______ =:,.~
11?rollle s/;aficrrm and screwaS'sembly
-- ---- ___ Torol/le conneclor rod
--_ ..
~-
4-31. Antipercolating device. Closing of throttle causes small valve (sixth
arrow from top) to be lifted from a port, relieving vapor pressure in high-speed
circuit. (Pontiac Motor Division of General Motors Corporation)
FIG.
air hom is low, less air bleeds into the main nozzle, thus compensating for the reduced vacuum in the ventmi, which tends to
pull less gasoline from the nozzle.
Similar air bleeds are used in the idle-and-low-speed circuits of
carbmetors as explained in §60.
§80. Compensating system Several carbmetor models use a compensating system (Fig. 4-32) which has the job of compensating
for variations in fuel flow from the main nozzle. The main nozzle
tends to discharge more fuel as engine speed (and air speed through
[101]
Automotive Fuel, Lubricating, and Cooling Systems
§80
air horn) increases. This tendency may cause an excessively rich
mixture at higher speeds. But the compensating system, which includes a compensating nozzle, works in the reverse manner; it tends
to lean out the mixture as engine speed increases. Thus, the main
nozzle and the compensating nozzle work together to provide a
mixture of uniform richness throughout the operating range. Fuel
FIC.
4-32. COJnpensating system in an updraft carburetor. (Zenith)
for the compensating nozzle enters the compensating well through
the compensating jet (see Fig. 4-32). At low engine speeds (when
the main nozzle is not discharging very much fuel), the compen··
sating nozzle discharges enough fuel to provide a satisfactory rich
mixture. But as engine speed increases, fuel flows through the compensating nozzle faster than it can enter the well through the jet.
The fuel level falls in the well, uncovering the air-bleed holes. Now,
air begins t'Q bleed into the compensating nozzle; the compensating
nozzle db'Charges a leaned-out mixture. Meantime, however, the
[102]
\.
§80
Carburetor Fundamentals
main nozzle discharges more fuel as engine speed increases. The
combination provides a properly proportioned mixture for the
operating condition.
CHECK YOUR PROGRESS
Progress Quiz 2
Once again you have the opportunity to check your progress in your
studies of the automobile. The quiz that follows allows you to check up
on yourself to determine how well you are remembering the facts you
have been reading on the carburetor. Some of the questions may be a
little hard for you to answer, but don't let that discourage you. Just
reread the pages in the book that will give you the answers. This review,
and answering the questions, will fix the important facts in your mind.
Completing the Sentences
The sentences below are incomplete. After each sentence there are
several words or phrases, only one of which will correctly complete the
sentence. Write each sentence down in your notebook, selecting the
proper word or phrase to complete it correctly.
1. In the accelerator-pump circuit fuel is forced into the air hom by
movement of a
check valve
metering rod
discharge
nozzle
piston
2. Dual carburetors (with two air horns) have accelerator-pump cirdischarge nozzles
cuits with two
metering rods
pistons
pumps
3. The purpose of connecting the accelerator-pump piston to the
throttle linkage through a spring is to give the fuel spray from the
accelerator-pump circuit
higher pressure
longer duration
shorter duration
faster starting
4. Closing the choke valve when cranking or running the engine proincreases air
duces a vacuum in the carburetor air horn which
flow
leans out mixture
increases fuel discharge from main
nozzle
5. The most commonly used automatic choke is operated by
vacuum and solenoid
vacuum and thermostat
thermostat
and temperature
6. As the engine warms up, winding up of the thermostat in the automatic choke causes the choke valve to
close
release
vacuum piston
open
7. When the engine is cold, opening of the throttle valve (which re[103]
Automotive Fuel, Lubricating, and Cooling Systems
duces intake-manifold vacuum) causes the vacuum piston to be
released; this causes the choke valve to
move toward closed
position
move toward open position
be held stationary
8. When the engine is cold, the manifold heat control causes hot exhaust
exhaust manigases to circulate through a jacket around the
fold
intake manifold
exhaust pipe
tail pipe
throttle
9. The fast-idle cam is rotated by linkage connected to the
idle ad;ustment screw
choke valve
10. The purpose of the antipercolator is to relieve vapor pressure and
thereby prevent boiling of'the fuel from the
main nozzle
percolator circuit
drip circuit
idle circuit
CHAPTER CHECKUP
NOTE: Since the following is a chapter review test, you should review
the chapter before taking the test.
You have already taken a couple of progress qu:zzes as you went
through the chapter. Now, you can take a general checkup test on the
entire chapter. This helps you review again the essential points covered
in the chapter. Repeated review of the important facts fixes them firmly
in your mind. Then, when you get into the shop or are confronted with a
problem on carburetors, you won't have to grope around in the dark. The
facts will be there in your mind, ready to help you. If any of the questions
that follow stump you, don't be alarmed. Just review the chapter again to
get the facts "down pat." Write the answers in your notebook. This helps
you remember and also assembles all the important facts on the subject
in one place for your easy reference.
Correcting Parts Lists
The purpose of this exercise is to help you spot unrelated parts in a list.
For example, in the list idling circuits, float bowl, idle passage, idle adjustment screw, idler gear, the only part that is not in the carburetor
idling system is the idler gear. This name, therefore, does not belong.
In each of the lists below, you will find one item that does not belong.
Write down each list in your notebook, but do not write down the item
that does not belong.
1. Carburetor parts include air horn, throttle valve, main nozzle, exhaust pipe, venturi.
2. Carburetor circuits include idling-and-Iow-speed circuits; float circuit; high-speed, part-load circuit; ignition circuit; high-speed, fu11power circuit.
3. Float-circuit parts include float bowl, float, needle valve, vent, float
rings. \.
[104]
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Carburetor Fundamentals
4. Idling circuit includes float bowl, idling-and-low-speed passage, idle
adjustment screw, idle gears.
5. Full-power circuit may include such items as main nozzle, recharge
lever, vacuum-operated piston, metering rod, metering-rod jet.
6. Accelerator-pump circuit includes pump piston, check valve, discharge nozzle, linkage to throttle, main nozzle.
7. Automatic choke may include such items as choke valve, thermostat,
solenoid diaphragm, vacuum piston.
8. Special features of carburetors include such items as air bleed, oil
bleed, antipercolator, throttle cracker, fast-idle cam.
Completing the Sentences
The sentences below are incomplete. After each sentence there are
several words or phrases, only one of which will correctly complete the
sentence. Write each sentence down in your notebook, selecting the
proper word or phrase to complete it correctly.
1. The circuit in the carburetor that is responsible for maintaining a
fuel circuit
carburetor circuit
constant-level reservoir of fuel is called the
level reservoir
float circuit
2. When the engine is idling, all the fuel burned by the engine must
pass the
idle adjustment screw
idle-speed setscrew
main nozzle
3. Float bowls may be vented in either of two ways,
or atmosphere
air cleaner
to main nozzle or idle circuit
to atmosphere or float
to air horn
to float or
4. When the float bowl is vented to the atmosphere, the carburetor is
a balanced carburetor
a dual carburetor
an unbalanced carburetor
5. With the throttle only slightly opened, intake-manifold vacuum
causes
venturi action
fuel discharge from main nozzle
fuel discharge from low-speed port
6. With the throttle wide open, venturi action, producing a vacuum,
causes
fuel discharge from main nozzle
fuel discharge from
low-speed port
fuel discharge from accelerator jet
7. As the throttle valve is moved from the closed to the opened position,
lowa spray of fuel is discharged into the air horn from the
speed port
nozzle
accelerating-pump jet
idle port
main
8. As the carburetor full-power circuit begins to function, additional fuel
is delivered to the main nozzle due to the movement of a
thermostat or butterfly valve
metering rod or vacuum
piston thermostat and vacuum piston
[l05]
I
Automotive Fuel, Lubricating, and Cooling Systems
9. In the automatic choke the position of the choke valve is controlled
by
metering rod or vacuum piston
thermostat and
vacuum piston
fast-idle cam or throttle linkage
10. The fast-idle cam, which is linked to the automatic-choke valve,
causes the engine to idle fast when the engine is
cold
warm
overheated
Purpose and Operation of Components
In the following, you are asked to answer questions about certain components in the fuel system, discussed in the chapter you have just finished.
If you have any difficulty in writing down your explanations, turn back
into the chapter and reread the pages that cover the item you are writing
about. Then write down your explanation. Don't copy; try to tell it in
your own words. This is a good way to fix the information in your mind.
Write in your notebook.
1. What are the names of the circuits of the carburetor?
2. How do the float and needle valve work to maintain a constant fuel
level in the float bowl?
3. What two ways are float bowls vented, and what are the names given
to carburetors with these two venting methods?
4. How does the metering rod work when the full-power circuit goes
into operation?
5. How does the accelerator pump operate?
6. How does the automatic choke operate?
7. What is the purpose of the manifold heat control, and how does it
operate?
8. What is the purpose of the anti-icing circuits discussed in the book?
9. What is the purpose of the throttle cracker?
10. What is the purpose of the antipercolator?
SUGGESTIONS FOR FURTHER STUDY
Continue your studies of actual fuel-system components in your school
shop or automotive service shop. As you handle carburetors and carburetor parts, you will understand more clearly how these units operate
and what the various parts do in the complete working assembly. Manufacturers of carburetors and automobile engines prepare service manuals
for the use of engine servicemen. If you can borrow these from your
school automotive shop library or from a friendly service shop, study
them carefully, for they have much valuable information in them. Write
down in your notebook important points about carburetors that you
might learQ- in the shop or from the manuals.
\
[106]
\
"\,
! \
\
5: Aulomolive cal'bul'etol's
THE PURPOSE of this chapter is to describe different accessory
devices used on modern carburetors and to discuss in detail various
carburetors used on modern automotive vehicles.
§81. Accessory devices on carburetors In previous chapters we discussed the various circuits and devices on automotive carburetors
that contribute to good engine performance under various operating
conditions. These circuits and devices include the idling-and-lowspeed circuits, the high-speed circuits, accelerator pump, choke,
and manifold heat control. In addition to these, various carburetors
have special accessory devices that do certain specific jobs on the
vehicle, such as:
l. Vacuum circuits to control the ignition-distributor spark
advance.
2. Electric switches to operate the starting-motor control circuit.
3. Throttle-return checks and magnetically controlled dashpots
to retard throttle closing under certain conditions.
4. Electric kick-down switches that are tied into the operation of
certain types of automatic transmissions.
5. Governors to control or limit top engine speed.
§82. Ignition-distributor controls The vacuum circuits to ignition
distributors have already been mentioned briefly in the note at the
end of §60. The purpose of such circuits is to carry intake-manifold
vacuum into the ignition distributor when the throttle valve is
opened just past the idle position. During idle and low-speed operation there is vacuum in the intake manifold, and this means that
less air-fuel mixture will enter the cylinders. The mixture will be
less highly compressed and will burn more slowly on the combustion stroke. In order to obtain more power from the mixture under
these conditions, the ignition spark must occur earlier in the cycle.
[107]
Automotive Fuel, Lubricating, and Cooling Systems
§82
This is accomplished by carrying intake-manifold vacuum to a
vacuum-control device on the distributor (Fig. 5-1). When the
throttle valve swings past the vacuum opening in the carburetor air
horn (Fig. 5-1), intake-manifold vacuum acts through the vacuum
passage and causes a spring-loaded diaphragm to move inward. In
the unit shown, this causes the distributor to rotate a few degrees
in its mounting. As a result, the distributor contact points open
earlier in the cycle to produce a spark advance. The mixture therefore gets an earlier start in its combustion and has more time to give
up its power to the downward-moving piston. On other distributors
FIG. 5-1. Vacuum-line connection between distributor vacuum-advance mechanism and carburetor. (Delco-Remy Division of General Motors C01'poration)
the breaker plate in the distributor is rotated instead of the complete distributor.
Another variation of this type of control is illustrated in Fig. 1-26.
The carburetor with which it is used is shown in sectional view in
Fig. 5-2. There are two vacuum-line connections into the carburetor air horn. The lower connection at B operates as described in
the previous paragraph and supplies an advance based on intakemanifold vacuum. The upper connection at A supplies a spark advance based On engine speed. The higher the speed, the faster the
air moves through the venturi. This means an increased vacuum
and a greater spark advance. This advance, based on speed, gives
the air-fuel mixture in the cylinders enough time to ignite, burn,
[108]
\
,\
\
\.
Automotive Carburetors
§83
and give up its power to the pistons. Other distributors use a centrifugal device to obtain spark advance based on speed (§§19 and
20).
The subject of distributor-advance mechanisms is covered in
detail in another book in the McGraw-Hill Automotive Mechanics
Series (Automotive Electrical Equipment).
sllOwing vacuum passage and points, A and B, at which vacuum is obtained .
(Ford Motor Company)
§83. Starting-control switches Figure 5-3 illustrates a ball-type,
vacuum-controlled switch which controls the action of the starting
motor. This switch is located in the carburetor. To start the engine,
the ignition switch is turned on and the throttle is opened. As the
throttle is opened, the throttle shaft turns, forcing the ball in
against the switch plunger. The plunger is thereby forced to move
in against the return spring so that the contact spring connects between the two switch terminals. Electric current now flows through
the switch. This current operates electromagnetic controls on the
starting motor. These controls, in turn, connect the starting motor
to the battery so that starting takes place. Mter the engine starts
[109]
Automotive Fuel, Lubricating, and Cooling Systems
§84
and the throttle is released, the intake-manifold vacuum pulls the
ball upward out of the way. Now, the throttle can be operated and
the throttle shaft turned without operating the switch. Further
details of starting-motor conb'ols are found in Automotive Elect1'ical
Equipment, another book in the McGraw-Hill Automotive Mechanics Series.
§84. Throttle-return checks On some carburetors used on certain
cars with automatic transmissions, a device to prevent sudden closing of the throttle is incorporated. Such a device is desirable since
sudden closing of the throttle might cause momentary hesitation
of the engine. With automatic transmissions incorporating a fluid
coupling or torque converter, there is some flexibility in the coupling
between the engine and car wheels. Thus, if the throttle were closed
suddenly, the engine might slow down very rapidly. Slippage in the
coupling would permit this even though the car were moving at
good speed. The rapid slowdown of the engine, as it was suddenly
throttled down, could so unbalance carburetor action as to cause a
momentary hesitation in the engine.
To prevent this, many carburetors on cars equipped with automatic transmissions use a throttle-return check. Figure 5-4 illush'ates one type of check. It contains a spring-loaded diaphragm
which trap~
air behind it when the throttle is opened, and the shaft
and adjusting screw on the check move outward. Then, when the
[110]
\
\
\
Automotive Cm'buretm's
§84
throttle is :released, the contact arm on the throttle lever moves
against the check adjusting screw. Since the air trapped back of
the spring-loaded diaphragm can escape only slowly, the throttle
is checked at this point and moves on to the closed position with
relative slowness.
Another type of tln-ottle-return check is shown in Fig. 5-5. In
this unit, called a dashpot, the mechanism is controlled by a small
electromagnet which causes the dash pot to check the throttle retmn
~
FIG. 5-4. Throttle-return check on carburetor. (Chevrolet Motor Division of
Geneml Motors Corporation)
at some times but not at others. A speed-governor device on the
transmission determines when the dashpot should work. Above a
certain speed (governed speed of transmission), the electromagnet
is not operating and the check ball is not seated. Thus, the air
passage back of the dashpot diaphragm is open and the dashpot
offers no restriction of closing of the throttle. However, at lower
speeds, the electromagnet is energized and the check ball seated.
This restricts air How and retards dashpot diaphragm movement
and thus throttle closing.
Also used on the carburetor illustrated in Fig. 5-5 is a speCial kickdown switch which operates when the throttle is depressed to wide[Ill]
Automotive Fuel, Lubricating, and Cooling Systems
§85
open position with car speeds below 40 to 45 mph (miles per hour) .
Above this speed the intake-manifold vacuum holds the kick-down
switch piston up so the switch cannot work. The purpose of this
switch is to provide a means for the driver to shift down to a lower
transmission gear automatically by simply pushing the throttle
down.
DISCHARGE NOZZLES
GASKET
BAFflE PLATE
HEAT RETAIN ER PLATE
CLIMATIC CONTROL HOUSING
GASK
METERING ROD
DUST COVER
VACUOMEfER
LINK
METERING ROD
UFTER ARM
ACTUATING ARM
DASH POT PLUNGER PLATE
DASH POT DIAPHRAGM
DASHPOT MAG N ET ./'
FIG . 5-5. Carburetor cut away to show dashpot, kick-down switch, and choke
construction. (Chrysler Sales Division of Chrysler Corporation)
Operation of various automatic transmissions and transmission
controls is covered in detail in another book in the McGraw-Hill
Automotive Mechanics Series (Automotive Transmissions and
Power Trains) .
Engine-speed governors prevent overspeeding of
the engine. They are used primarily on trucks and busses and have
two purposes, to prevent excessive vehicle speed and to prevent
excessive engine wear. A truck is designed to have satisfactory highspeed performance when loaded. Thus, when unloaded, it could
operate at excessively high and dangerous speeds. Not only does
this increase the chances of an accident, but also it overspeeds the
engine, thus increasing engine wear. But a truck engine can also be
§85. Governor
[112]
Automotive Carburetors
§85
overspeeded at low vehicle speeds. For example, suppose the safe
maximum engine speed is 3,600 rpm (revolutions per minute).
Suppose this gives the truck a level-road speed, when loaded and in
high gear, of 60 mph. But suppose the driver shifts to a low gear to
pull up a hm. Without a governor, he could very well overspeed the
engine. For instance, suppose the gear ratio is such as to give 10
mph at 3,600 engine rpm. But the driver holds the accelerator down
so that the truck speed increases to 15 mph. This means the engine
is turning at 4,800 rpm. Such high engine speed is very damaging
to the engine and greatly shortens the life of bearings and other
engine parts.
To prevent such damage and reduce accident hazards from high
vehicle speeds, governors are used. They are of two general types,
the centrifugal type, and the velOcity and vacuum types.
1. Centrifugal type. The centrifugal governor is driven mechanically from the engine. It has centrifugal weights that move out
against gravity Or spring tension as engine speed increases. This
movement is carried by mechanical linkage to the carburetor and
throttles down the air-fuel flow to the engine as maximum-rated
engine speed is reached. The throttling action may take place
directly on the throttle valve in the carburetor (by imposing a closing force on it) or on a separate butterfly valve placed below the
throttle valve.
2. VelOcity and vacuum types. VelOcity and vacuum types of governors mount between the carburetor and the intake manifold
(Figs. 5-6 and 5-7). The velocity type of governor has a throttle
plate that is mounted off center. It is held open by a spring. As
engine speed increases, the air-fuel mixture moves faster through
the carburetor air horn and through the governor. The increased
velocity of the air-fuel mixture tends to close the governor throttle;
it strikes the unbalanced part of the throttle and pushes it toward
the closed position. Opposing this force is the spring tension. As
governed speed is attained, the two opposing forces position the
throttle in a partly closed position. This position admits just enough
air-fuel mixture to maintain governed speed. The vacuum type of
governor works in almost the same way except that the closing force
comes from intake-manifold vacuum. Intake-manifold vacuum increases with increased speed. This increasing vacuum acts on a
vacuum piston that is linked to the governor throttle. The vacuum
[113]
Automotive Fuel, Lubricating, and Cooling Systems
§85
tries to close the throttle; a spring tries to hold it open. A balance of
forces is struck when the governed speed is attained. The throttle
is held open just enough to admit sufficient air-fuel mixture for the
engine to maintain governed speed.
Intake manifald- - - - -
FIG. 5-6. Velocity, or vacuum, type of governor mounted between intake mani-
fold and carburetor.
FIG. 5-7. Velocity, or vacuum, type of governor with carburetor removed to
show governor throttle valve.
3. Combination centrifugal-vacuum governor. One type of governor operates on both principles (centrifugal and vacuum). The
centrifugal unit is mounted on the ignition distributor; the centrifugal weights operate an air-bleed valve. The vacuum unit is
mounted on the carburetor; it contains a diaphragm which is linked
[114]
\
Automotive Carburetors
§86
to- the throttle-valve shaft. In operation, increased engine speed
causes the centrifugal unit to shut the air-bleed valve. This closes a
passage to the vacuum unit. Now, intake-manifold vacuum can
actuate the diaphragm in the vacuum unit; this causes the throttle
valve to be moved toward the closed position and thus prevents
any further increase of engine speed. The engine is held at governed speed.
§86. Carburetor assembly All the features discussed in previous
sections may not be incorporated in a single carburetor. But dif-
FIG. 5-8. Carburetor in sectional view. Because of the difficulties of showing
all features in one view, the accelerator-pump system is shown on the left side
of the air horn. Actually, it is part of the Roat-bowl system at the right. The
throttle connector rod is shown twice, although there is only one. It is connected to both the accelerating-pump lever and the metering rod. (Chevrolet
Motor Division of General Motors Corporation)
ferent carburetors use various combinations of these features. The
carburetor is a remarkable device since it maintains a fairly constant
air-fuel-mixture ratio throughout the normal intermediate driving
range and also enriches tlle mixture when a rich mixture is required
for starting, warm-up, and high-speed operation. Figures 5-8 and
[115]
Automotive Fuel, Lubricating, and Cooling Systems
§87
5-9 are sectional views of carburetors having many of the features
described on previous pages. Other carburetor models are discussed
in following sections.
15-A
FIG. 5-9. A dual carburetor for an eight-cylinder in-line engine, Two air horns
and two low- and high-speed circuits are incorporated, each handling four
cylinders. (Buick Motor Division of General Motors Corpomtion)
1. Choke valve
12. Main-nozzle lead
20. Float
2. Power-piston
gasket
21. Float lever
vacuum passage
13. Secondary idle air
22. Float-needle-valve
3. Main nozzle
bleeder
clip
4. High-speed bleeder
14. Idle needle valve
23. Float fulcrum pin
IS. Idle discllarge ports
24. F loat needle valve
S. Idle air bleeder
6. Idle tube
15A. Idle channel25. F loat-needle-valve
reducer wire
7. Vacuum power
seat
16. Vacuum-spark
26. Float-hanger gaskets
piston
connection
8. Pump fulcrum arm
27. Float hanger
17. Throttle valve
9. Power bypass jet
28. Gasoline inlet
18. Primary venturi
10. Main-nozzle plug
29. Gasoline strainer
19. Auxiliary venturi
11. Main metering jet
30. Float-bowl vent
§87. Updraft carburetors The carburetors we have previously described are all known as downdraft carburetors. The ingoing ailmoves downward through the air horn. Some carburetors are of the
updraft type; ill these units the ail- moves upwaJ'd through the air
horn. Downdraft carburetors are mounted on top of the intake
[116]
\
Automotive Carburetors
§87
manifold. But updraft carburetors are mounted below the intake
manifold; the air-fuel mixture flows upward from the carburetor
into the intake manifold. Updraft carburetors are used on applications where there may not be enough headroom above the engine
to accommodate a downdraft carburetor. Essentially, both types
of carburetor operate in the same manner. Typical updraft carburetors are described in the following paragraphs.
1. Float circuit. Figure 5-10 shows, in sectional view, the float
circuit of an updraft carburetor. The float circuit includes a needle
valve actuated by a lip on the float arm, as in other carburetors. As
Choke valve
FIG. 5-10. Float circuit in updraft carburetor. (Carter)
the float bowl fills, the float moves up, thereby causing the lip to
push the needle valve into its seat and shut off the fuel flow. Note
that the float bowl is vented into the carburetor air horn (on atmospheric side of choke valve); the carburetor is balanced (see §57).
2. Idle circuit. The idle circuit in the updraft carburetor (Fig.
5-11) operates in much the same way as the idle circuit in the
downdraft carburetor. It includes an idle-passage tube connecting
the float bowl with the idle ports, an idle adjustment screw, idle air
bleed, and idle ports. When idling with a closed throttle, fuel is
delivered past the pointed tip of the idle adjustment screw. If the
throttle valve is opened a little so that its edge moves past the
secondary idle port, then it, also, beginS to deliver fuel. Air from
[117]
Automotive Fuel, Lubricating, and Cooling Systems
§87
the air bleed is mixed with the hIel as it moves upward around the
idle-passage tube.
3. High-speed circuit. The high-speed circuit in the updraft
carburetor (Fig. 5-12) also operates much like the high-speed cir-
passage tube
FIG.
5-11. Idle circuit in updraft carburetor. (Carter)
Step-up pistan spring
Main
assembly
5-12. High-speed circuit in updraft carburetor. Arrows represent air How,
dashed lines fuel flow . (Carter)
FIG.
cuit in other carburetors. As the throttle is opened, air flow
through the venturi increases. Tllis causes the main nozzle to start
discharging fuel. There is a vent from the upper part of the float
bowl to the main-nozzle assembly. Air enters the main nozzle
[118]
/\
\,
§87
Automotive Carburet01's
through this vent and through a series of holes in the lower end of
the main-nozzle tube. Thus, some premixing of air and fuel takes
place before the fuel is discharged from the nozzle.
4. Full-thmttle operation. When the throttle is only partly
opened, there is sufficient vacuum in the intake manifold to hold
the step-up (vacuum) piston in the upper position. But when the
throttle is opened wide, the intake-manifold vacuum drops. This
allows the piston spring to push the piston down. The piston push
rod then opens the ball valve at its lower end. Additional fuel can
then feed past the opened ball valve into the main-nozzle circuit.
This gives a richer mixture for full-throttle, full-power operation.
pump piston
FIG. 5-13. Accelerator-pump circuit in updraft carburetor. ( Carter)
5. Accelemtor-pump circuit. The accelerator-pump circuit for an
updraft carburetor is shown in Fig. 5-13. When the throttle is
closed, linkage to the accelerator-pump piston lifts it upward. This
draws fuel from the :S.oat bowl past the intake check valve and
into the pump chamber below the piston. Then, when the throttle
is opened, the piston moves downward. Pressure on the fuel increases, causing the intake check valve to close and the discharge
valve to open. Fuel is discharged past the discharge valve under the
pressure of the pump-piston spring. This places the fuel in the line
to the main nozzle under pressure so that the main nozzle discharges additional fuel.
6. Idle circuit. The idle circuit of another type of updraft carburetor is shown in Fig. 5-14. On this unit the idle adjustment
screw serves a somewhat different purpose from that of the idle ad[1191
Automotive Fuel, Lubricating, and Cooling Systems
§87
justment screw on carburetors previously discussed. On this unit the
idle adjustment screw admits air into the fuel flowing through the
idle circuit from the float bowl. The more air is admitted, the less
fuel will flow to the idle discharge port. The fuel flows past the
compensating jet and compensating well, up through the idle jet
and calibration (or restricting orifice) , past the idle adjustment
.
Idle disc/Jorge
port
Colibration
FIG. 5-14. Idle circuit in updraft carburetor. (Zenith)
screw and idle-port plug. As the idle adjustment screw is turned
in or out, it admits less or more air into the fuel stream. Admitting
more air means that less fuel discharges from the idle port, which,
in turn, means that the idling mixture is leaner. This idle-ad justment-screw arrangement is used on several models of carburetors,
both updraft and downdraft.
7. Compensating system. Several carburetor models use a compensating, system, which has already been illustrated (Fig. 4-32 )
[120]
"
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Automotive CarburetO'rs
§87
and described (§80 ). The compensating system tends to lean out
the air-fuel mixture as engine speed increases, thereby compensating
for the tendency of the main nozzle to enrich the air-fuel mixture
as engine speed increases. The combination of compensating system
and main nozzle permits the carburetor to supply a properly
proportioned mixture for the various operating conditions. Figure
5-15 illustrates the high-speed circuit for a carburetor using a compensating system.
and
occeleratiflQ iet
FIG .
5-15. High-speed circuit in updraft carburetor. (Zenith )
8. Accelemtor-pump circuit. Figure 5-16 illustrates the accelerator-pump circuit of the updraft carburetor shown in Figs. 4-32,
5-14, and 5-15. This pump works in much the same manner as
accelerator pumps previously described. When the throttle is
closed, intake-manifold vacuum, operating through the vacuum
passage, draws the vacuum piston upward, compressing the piston
spring. This movement lifts the pmnp piston into the upper part
of the pump chamber. Then, when the throttle is opened, intakemanifold vacuum drops, releaSing the vacuum piston. The piston
spring forces the pump piston downward. The pressure on the
[121]
Automotive Fuel, Lubricating, and Cooling Systems
§88
fuel below the pump piston unseats the power valve and allows
fuel to flow through it and the power jet to the main nozzle. Extra
fuel is thereby discharged from the main nozzle to enrich the
mixture for acceleration. The power valve is also held open during
open-throttle, low-vacuum conditions; under these conditions, there
c
Vacwm piston
air vent passaqe
nozzle
Check valve
FIG. 5-16. Accelerator-pump and full-power circuit in updraft carburetor. A,
plug; B, vent; C, plug opening. (Zenith)
is insufficient vacuum in the intake manifold to hold the vacuum
piston up. It, along with the pump piston, moves to the bottom
position as shown in Fig. 5-16. The pump piston then holds the
power valve open. Now, extra fuel can flow past the power valve
to the main nozzle for wide-open throttle, full-power operation.
Carburetors of the downdraft type
a horizontal air entrance as shown in Fig. 5-17. The
§88. Horizo"tal air entrance
may also ~ave
[122]
~\
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Automotive Carburetors
.
§88
carburetor illustrated is a downdraft unit, but the air int_ake is
located at one side in order to save height. The carburetor contains
float, idle, low-speed, high-speed, and accelerator-pump circuits
similar to those already discussed. Note that the updraft carburetor
shown in Fig. 5-17 has horizontal air entrances; updraft carburetors
usually have this arrangement.
Fast/die screw
Choke counterweight
Slow idle screw -"111"'--_....
FIG. 5-17. Downdraft carburetor with horizontal air enb'ance. (Oldsmobile
Division of General Motors Corporation)
CHECK YOUR PROGRESS
Progress Quiz 3
Here is your progress quiz for the first half of the chapter. The questions below are here to help you. They give you an opportunity to find
out how wen you are remembering the essential details of the carburetors
you have just read about. Also, they help you review the facts you have
read, and this review fixes the facts more firmly in your mind. If you have
any trouble answering the questions, just reread the pages that will give
you the answers. Remember, most good students reread their lessons
several times to make sure they won't forget the essential facts in them.
Completing the Sentences
The sentences below are incomplete. After each sentence there are
several words or phrases, only one of which will correctly complete the
[123)
§89
Automotive Fuel, Lubricating, and Cooling Systems
sentence. Write each sentence down in your notebook, selecting the
proper word or phrase to complete it correctly.
1. In order to give the air-fuel mixture more time to burn during partthrottle operation, the ignition distributor must
retard the
spark
increase the spark
advance the spark
increase
the vacuum
2. Spark advance based on intake-manifold vacuum does not occur
until the throttle
is fully closed
is wide open
opens
a small amount
3. Automatic-type starting-control-switch action is based on both intakemanifold vacuum and
throttle movement
engine speed
choke position
4. Throttle-return checks are used on some cars equipped with
dash pots
power steering
automatic transmissions
power brakes
5. The device installed on some vehicles to prevent overspeeding of the
engine is called a
speeder
governor
control
brake
6. The velOCity-type governor is installed between the carburetor and
the
intake manifold
exhaust manifold
air cleaner
throttle valve
7. In the velOCity governor the throttle plate tends to move toward
the closed position as the velocity of the air-fuel mixture through
the carburetor air horn
decreases
increases
strikes a
balance
8. Carburetors may be divided, according to the direction of air flow
through the air horn, into
downdraft and updraft
forced
draft and free draft
horizontal draft and vertical draft
9. In some carburetors the idle adjustment screw admits air-fuel mixture into the air horn; in others, it admits air into the
mainnozzle circuit
updraft
idle circuit
high-speed circuit
10. The main purpose of the compensating system is to compensate for
variations in fuel flow from the
idle circuit
low-speed
circuit
main nozzle
In eight-cylinder in-line and V-8 engines it
is common practice to use a dual carburetor with dual-type intake
manifolding. In a dual carburetor there are two separate air
horns (or barrels), two venturis, two main fuel nozzles, and two
throttle valve!!. The two throttle valves are attached to a common
throttle shaft so that both valves open and close together. Figures
[124]
\
§89. Dual carburetors
\
\
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\
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Automotive Carburetors
§89
4-3, 4-11, and 5-5 are different views of dual carburetors. The dual
carburetor provides, in effect, two separate single-barrel carburetors,
each carburetor feeding four of the cylinders. Each carburetor
barrel feeds into one section of a dual-type intake manifold. Figure
FIG. 5-18. Fuel distribution through two air horns in dual carburetor and intake
manifolds on an eight-cylinder in-line engine. (Buick Motor Division of General
Motors Corporation)
FIG. 5-19. Fuel distribution through two air horns and dual-intake-manifold
system of dual carburetor on V-8 engine. (Studebaker Corporation)
5-18 shows the air-fuel-mixture delivery pattern for an eightcylinder in-line engine. One carburetor barrel supplies cylinders
3,4, 5, and 6. The other carburetor barrel supplies cylinders 1,2, 7,
and 8. The delivery pattern for a V-8 engine is shown in Fig. 5-19.
In this pattern, each carburetor barrel supplies two cylinders in
[125]
Automotive Fuel, Lubricating, and Cooling Systems
§90
each bank as indicated by the arrows. This arrangement assures
greater uniformity of fuel delivery to all cylinders. If a single barrel
were used to supply all eight cylinders, the most distant cylinders
would get less air-fuel mixture than the nearby cylinders. The end
cylinders in an in-line engine, for example, would be starved. Inferior engine performance would result. But by using a two-barrel,
or dual, carburetor, the intake manifolding can be arranged so that
all cylinders being fed from a barrel will be about equally distant
from the barrel. Thus, all cylinders receive approximately the same
amounts of air-fuel mixture.
\
§90. Four-barrel carburetor The four-barrel carburetor (Figs. 5-21
to 5-25) consists, in effect, of two dual carburetors combined into
a single assembly. The carburetor assembly has four air horns, or
barrels, each with its own venturi, throttle valve, and main fuel
nozzle. Since it has four barrels, and thus four main nozzles, or fuel
jets, it is often called a quadrifet carburetor. One set of air horns,
or barrels, makes up a primary dual carburetor. The other pair
makes up a secondary dual carburetor. The primary dual carburetor is responsible for delivery of air-fuel mixture to the engine
under most operating conditions. The primary dual carburetor, or
primary side, as it is called, contains a full complement of circuits,
including idling-and-low-speed circuit, high-speed circuit, accelerator-pump circuit, and choke circuit. Thus, under most operating
conditions, it alone takes care of engine requirements. However,
when the throttle is moved toward the wide-open position for
acceleration or full-power operation, then the secondary dual carburetor, or secondary side, comes into operation and supplies additional air-fuel mixture. This combination permits satisfactory and
economical part-throttle operation. At the same time, improved
full-throttle operation is attained, since with wide-open throttle,
the passage space for air-fuel mixture to enter the engine is doubled
(from two to four barrels). Greater amounts of air-fuel mixture
can enter the engine for improved high-speed, full-power performance. The following paragraphs describe the features of this
carburetor.
1. Manifold. Since there are four barrels in this carburetor, the
intake manilold must have four openings at the carburetor mounting pad, t'Yo for the primary-side barrels and two for the secondary[126]
\
Automotive Carburetors
§90
side barrels (Fig. 5-20). When the primary side only is in operation,
then the two openings (marked P in the illustration) deliver airfuel mixture to the cylinders. One handles cylinders 1, 4, 6, and 7.
The other handles cylinders 2, 3, 5, and 8. When the secondary side
comes into operation, its two barrels augment the air-fuel-mixture
delivery of the primary-side barrels. Delivery patterns are shown
by long arrows (primary side) and short arrows (secondary side)
in the illustration.
FIG. 5-20. Intake manifold for four-barrel carburetor. P indicates the primary
barrels. Air-fuel-mixture delivery from these is shown by long arrows. S indicates
the secondary barrels. Air-fuel-mixture delivery from these is shown by short
arrows. (Oldsmobile Division of General Motors Corporation)
2. Float circuit. Figure 5-21 illustrates the float circuit of the carburetor assembly. The primary and secondary sides of the assembly
(each consisting of two barrels) have their own float circuits with
separate float assemblies and needle valves. The two float bowls are
separated by a partition, but both vent into the carburetor air
horn. A connecting passage between the two float bowls permits
the fuel levels and air pressures to balance between the two float
bowls.
3. Low-speed circuit. During part-throttle operation, the primary
dual carburetor (or primary side) functions in the same way as a
standard dual carburetor (§89). Delivery pattern of the air-fuel
mixture to the cylinders is as shown by long arrows in Fig. 5-20.
The idle-and-Iow-speed circuit of the carburetor is shown in Fig.
[127J
Automotive Fuel, Lubricating, and Cooling Systems
§90
5-22. This illustration shows the primary and secondary sides
separated so the circuits can be seen. Actually, they are one assembly as shown in Fig. 5-21 or 5-24. Note that, on the carburetor
model illustrated, the secondary side has a fixed idle circuit. A
fixed amount of air-fuel mixture can discharge through it. The
primaJ.'y side has standard adjustable idle circuits (one for each
barrel) . Adjustment can be made on the primary side alone (by
PRIMARY SIDE
I;ECONDARY SIDE
FIG. 5-21. Float system of four-barrel carburetor. (Oldsmobile Division of General Motors Corporation)
turning the idle adjustment screw) to provide correct idle-mixture
richness.
Other carburetors of this type do not have any idle or low-speed
ports or circuits in the secondary side. On these, the primary side
alone supplies fuel for idling and low-speed operation.
The carburetor contains a vapor-vent ball check that opens as the
accelerator-pmnp countershaft returns to the closed-throttle position. Opening of the vapor-vent ball check provides a vent through
which fuel vapors can escape from the float bowls so that percolation will not occur (see §78).
[128]
\
..
Automotive Carburetors
§90
[129]
§90
{1S0]
Automotive Fuel) Lubricating, and Cooling Systems
\
\
\.
Automotive Carburetors
§90
4. High-speed circuit. As the throttle is opened and nears the
wide-open position, the two barrels on the secondary side come
into operation. The secondary throttle valves remain closed until
the primary throttle valves near the wide-open position. But from
that point on, they open rapidly with little further throttle movement so that they reach wide-open position along with the primary
throttle valves. With all throttle valves open, the condition shown
in Fig. 5-23 results. Now, air-fuel mixture is delivered through all
four barrels (see Fig. 5-20). Fuel flows from the secondary nozzles
after passing through fixed metering jets and fuel passages. On the
primary side, fuel delivery is through a combination mechanically
operated and vacuum-operated type of high-speed, full-power
circuit with metering rods controlled by a vacuum piston as well as
by throttle position (§67). The metering rods are lifted either when
the throttle is in the wide-open position or when there is little
vacuum in the intake manifold. In either case, lifting of the metering rods positions the smaller diameter of the rods in the meteringrod jets so that additional fuel is delivered through the fuel nozzles.
5. Accelerator-pump circuits. The accelerator-pump circuit is
shown in Fig. 5-24. This circuit supplies additional fuel for acceleration in the lower speed ranges. When the throttle is opened for
acceleration, the pump plunger is forced down by linkage to the
throttle. This action forces fuel out through the discharge passage,
past the discharge check, and through the pump jet into the passing
air stream. At higher speeds, no accelerator-pump action is necessary for smooth acceleration. To prevent accelerator-pump action at
higher speeds, the plunger linkage is so arranged as to cause the
plunger to bottom in the pump cylinder when the throttle has been
opened a predetermined amount. Thus, no pump action results
when the throttle is opened still wider. Note that the acceleratorpump circuit is in the primary side. The secondary side has no
such circuit.
6. Choke circuit. The choke circuit is shown in Fig. 5-25. Note
that there is a choke valve on the primary side only. The choke valve
is positioned by the thermostatic spring so that it is closed when the
engine is cold and open when the engine is hot. During warm-up,
the vacuum piston also helps to determine choke-valve position.
Vacuum in the intake manifold causes the vacuum piston to tend
to open the choke valve. But during acceleration, when the intake[1311
Autom.otive Fuel, Lubricating, and Cooling System.s
§90
[132]
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Automotive Carburetors
§90
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[133]
Automotive Fuel, Lubricating, and Cooling Systems
§91
manifold vacuum is reduced, the vacuum piston is released, permitting the choke valve to move toward the closed position. Operation of automatic chokes is covered in §72.
§91. Ford .carburetors 1. Six cylinder. The late-model Ford six-cylinder engines use the type of carburetor shown in Fig. 5-26. This carburetor is interesting because of its compactness and the use of a
transparent float-bowl cover (on left side in illustration). Figure
5-27 shows the carburetor partly cut away so that the idle passages
FIG. 5-26. Carburetor used on late-model Ford six-cylinder engines. (F01'd
Motor Company)
can be seen. Note the air bleed from the upper air horn and also
the fact that the carburetor uses a single venturi. There are two
discharge holes into the air horn, the lower of which supplies fuel
when the throttle is completely closed. When the throttle is opened
slightly, it swings past the upper hole so that it also begins to discharge fuel.
Figure 5-28, shows the carburetor partly cut away so that the
main fuel system and high-speed, full-power circuits can be seen.
The main discharge nozzle is located in the venturi and it begins
to feed fuel into the air stream when the engine speed reaches
about 900 or more rpm. Then, between approximately 900 and
[~34] ,
\
,
'.
Automotive Carburetors
§91
UPPER DISCHARGE
FIG.
5-27. Carburetor cut away to show idle circuit. (Ford Motor Company)
VALVE
VACUUM PASSAGE
FIG. 5-28. Carburetor cut away so that main fuel system and high-speed, fullpower circuits can be seen. (Ford Motor Company)
[135]
Automotive Fuel, Lubricating, and Cooling Systems
§91
1,250 rpm, both the idle circuit mentioned in the previous paragraph and the high-speed circuit work together to supply the fuel.
As the speed increases still more, the idle circuit fades out, and the
high-speed circuit alone is responsible for supplying fuel to the
engine. The high-speed air bleed introduces air into the fuel passing through the high-speed circuit before it reaches the main discharge. The fuel is discharged from the main discharge nozzle
I
PUMP OUTLET
VA'"
FIG. 5-29. Carburetor cut away so accelerating system can be seen. (Ford Motor
Company)
directly against the lower side of the choke valve. This helps to
vaporize it and mix it with the passing air.
For high-speed operation or under heavy load, as when climbing
a hill, additional power is desirable, and this means opening the
throttle wider. This action reduces the vacuum in the intake manifold. With a high vacuum, the diaphragm, rod, and spring combination holds the power valve closed. But with reduced vacuum,
the diaphragm is released, and this allows the spring to open the
power valve. When the power valve opens, an added passage for
fuel is op-ened in the high-speed circuit. Additional fuel is supplied
[136]
A
\
\
Automotive Carburetors
§91
to handle the added power demand of the high-speed or heavy-load
operation.
Figure 5-29 shows the carburetor cut away so that the accelerating system can be seen. When the throttle is opened for acceleration, the operating rod and spring impose pressure on the
diaphragm. The diaphragm therefore moves, forcing fuel in the
pump chamber out past the outlet valve, through the drilled
passage, and through the pmnp discharge outlet. When the throttle
DISTRIBUTOR
VACUUM
L_.
IDLE MIXTURE
FIG. 5-30. Carburetor used on late-model Ford V-8 engines. (Ford Motor
Company)
is released, the diaphragm spring returns the diaphragm to its
original position. Additional fuel is drawn into the pump chamber
past the inlet check valve.
2. Eight-cylinder cm·buretor. A late-model carburetor for a Ford
V-8 engine is shovm in Fig. 5-30. This is a dual carburetor (two
barrels) designed to use an air cleaner tllat mushrooms over and
surrounds the main body. The construction gives the carburetor a
somewhat dillerent appearance, but it operates in essentially the
same manner as other dual carburetors. Figure 5-31 shows how the
carburetor air cleaner is assembled on the carburetor.
[137]
Automotive Fuel, Lubricating, and Cooling Systems
§91
Figure 5-32 shows the carburetor cut away so that the idle circuit
can be seen. The fuel passes through the main jet and idle passage
to the discharge holes at the throttle valves. Each barrel has its own
discharge holes, feeding from the common idle passage in the main
body. Note that there is an idle-air-bleed opening in the main body.
When the throttle is closed, fuel feeds through the lower discharge
opening only, past the idle-mixture screw. But when the throttle
is opened a little, it swings past the upper discharge hole so that it
also beginS to discharge fuel into the air stream.
5-31. Phantom view showing how air cleaner sits down over the carburetor,
so that the main body of the carburetor is actually located inside the air cleaner.
(United Specialties Company)
FIG .
The main power circuit is shown in Fig. 5-33. The fuel passes
through the main jet from the float bowl, up through the main
well and down through the two main discharge nozzles into the two
barrels of the carburetor. The main well contains an air bleed at its
upper end.
For full-power, high-speed operation the throttle is moved toward
the wide-open position. This causes a loss of vacuum in the intake
manifold. With a high vacuum, the diaphragm holds the power
valve up ~ the closed position. But when the throttle is opened
so that ~cum
is reduced, the diaphragm moves downward under
[138]
A.,
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Automotive Carburetors
§91
spring pressure, permitting the power valve to open. Now, increased fuel can flow through the power-valve restriction and into
the main well. Additional fuel is therefore delivered from the well
by the main nozzles to handle the added power demands.
FIG. 5-32. Carburetor cut away so the idle circuit can be seen. (Ford Motor
Company)
Figure 5-34 shows the accelerating system of the carburetor. The
carburetor uses a pump piston which is linked to an operating rod
to the throttle. When the throttle is opened for acceleration, the
pump piston is forced downward, causing a discharge of fuel from
the pump outlet into the barrels.
[139]
NOZZLE TUBE EXTENSION
FIG.
PUMP OUTLET
.......,.....---
FIG.
[140J
POWER VALVE RESTRICTION
5-33. Main power circuit of carburetor. (Ford Motor Company)
5-3f Accelerating system of carburetor. (Ford Motor Company)
1\
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Automotive Carburetors
§92
§92. Multiple-carburetor installations For additional performance,
it is possible to install more than one carburetor on an engine. On
racing engines and other applications where maximum possible performance is desired, there may ?-ctually be one carburetor for each
cylinder. This, however, is unusual. For automotive applications,
REAR CARllURETOIt
(SECONDARY)
CENTER CARBURETOR
(PRIMARY)
fRONT CARBURETOR
(SECONDARY)
5-35. Three two-barrel carburetors mounted on a single engine. (Chevrolet Motor Division of General Motors Corporation )
FIG.
two or three carburetors may be installed on one engine. For example, Fig. 5-35 shows a three-carburetor installation on a Chevrolet
V-8 engine. A special intake manifold is required on which the three
carburetors can be mounted. The three carburetors are interconnected by mechanical and vacuum linkage. The center or primary
carburetor supplies all fuel when the throttle is less than 60-degrees
open. When the throttle is opened beyond 60 degrees, the linkage
opens a vacuum slider valve mounted on the center carburetor.
[141]
Automotive Fuel, Lubricating, and Cooling Systems
§92
Vacuum from the vacuum pump (an integral part of the fuel pump)
is now applied to the large diaphragm mounted on the front secondary carburetor. This diaphragm, therefore, is forced to move and
this movement is transmitted to the throttle valve of the front carburetor by a rod. The throttle valve of the front carburetor then
opens wide. This same movement is transmitted to the rear secondary-carburetor throttle valve by a rod so that this valve also opens
wide. The two secondary-carburetor throttle valves are therefore
both opened wide so the two secondary carburetors begin to feed
air-fuel mixture to the engine for improved acceleration and highspeed performance.
When the throttle valve is released, the vacuum slider valve is
closed. This shuts off the vacuum to the diaphragm so that it relaxes and the two secondary carburetor throttle valves close. Now,
the system performs as a single-carburetor system.
CHAPTER CHECKUP
NOTE: Since the follOWing is a chapter review test, you should review
the chapter before taking the test.
You are making excellent progress in your studies of automotive fuel
systems and have completed the part of the book dealing with the operation of gasoline-type fuel systems. The material you have studied thus far
in the book will be of considerable help to you when you go into the
automotive shop or office. This information helps you understand how
and why the fuel system components operate as they do. The later
chapters on fuel-system diagnosis and service will be much easier for
you when you understand the theory behind the units you work on.
The general checkup test that follows will help you review and remember
the essential facts you should know about carburetors. Write the answers
to the questions in your notebook. Writing the answers helps you remember them and also makes your notebook a valuable source of information to which you can refer in times of need.
Unscrambling the Devices
When the two lists below are unscrambled and combined, they will
form a list of the various devices used on carburetors and the applications
or purposes .of these devices. To unscramble the lists, take one item at a
time from the list to the left, and then find the item from the list to the
right that goes with it. For an example of how this is done, refer to
"UnscrambH{lg the Jobs" at the end of Chap. 3, "Fuel-System Operation." Writy the list down in your notebook.
[142]
\
\
Automotive Carburetors
for shifting to lower transmission gear
to control or limit top engine speed
for starting-motor control
for ignition-distributor spark advance
for cars with automatic transmissions
vacuum circuits
electric switches
throttle-return checks
kick-down switches
governors
Completing the Sentences
The sentences below are incomplete. After each sentence there are
several words or phrases, only one of which will correctly complete the
sentence. Write each sentence down in your notebook, selecting the
proper word or phrase to complete it correctly.
1. Many carburetors have a special vacuum circuit that is connected to
fuel pump
distributor
fuel tank
the
fuel gauge
ignition
2. Some carburetors have a special electric switch that is connected into
the
light circuit
horn circuit
starting-motor control circuit
air-
reshifts gears
3. Some carburetors contain a special dashpot, or check, that
tards throttle opening
retards throttle closing
4. The kick-down switch used on some carburetors has the job of producing
lower speed
higher vacuum
throttle retard
transmission downshift
centrifugal and velocity
dashkick-down and vacuum
speed and down-
5. Two types of governor are
pot and electric
shifting
6. There are two separate arrangements of the idle circuit and idle adjustment screw. In one, air-fuel mixture flows past the screw into the
air horn; in the other,
air flows past screw into idle circuit
air flows past screw to main nozzle
exhaust valves
throttle valves
intake manifolds
air flows past screw to venturi
7. In the dual carburetor there are two separate
intake valves
8. The most important function of the secondary side in the four-barrel
carburetor is to
improve wide-open-throttle performance
improve acceleration at part throttle
formance
improve low-speed per-
9. The Ford six-cylinder carburetor has
barrels
one barrel
two
four barrels
10. The Ford V-8 carburetor described in the book has its upper part
completely surrounded by
the float bowl
the air cleaner
the main venturi
the secondary venturi
[143]
Automotive Fuel, Lubricating, and Cooling Systems
Purpose and Operation of Components
In the following, you are asked to write down the purpose and operation of certain carburetor accessory devices discussed in the chapter. If
you have any difficulty in writing down your explanations, turn back into
the chapter and reread the pages that will give you the answer. Don't
copy, try to tell it in your own words. This is an excellent way to fix the
explanation firmly in your mind. 'Write in your notebook.
1. What is the purpose of the vacuum-controlled mechanism in the
ignition distributor?
2. Explain how the starting control switch described in the chapter
operates.
3. What is the purpose of the throttle-return check?
4. What is the purpose of the governor?
5. List the various circuits of the updraft carburetor as explained in the
chapter.
6. What is the reason for using a two-barrel, or dual, carburetor?
7. What is the function of the secondary side of the four-barrel carburetor?
8. List the circuits in the primary side of the four-barrel carburetor; in
the secondary side.
SUGGESTIONS FOR FURTHER STUDY
Refer to other books in the McGraw-Hill Automotive Mechanics Series
(Automotive Electrical Equipment and Automotive Transmissions and
Power Trains) for additional information on electric units and automatic
transmissions referred to in the chapter. You can also find out more about
these units in your school shop or in a friendly service shop. Possibly you
will be able to borrow car manufacturers' manuals from your school automotive shop library or from a service shop. Such manuals have much
valuable information in them about the electric units and automatic
transmissions and explain the manner in which the various units are tied
into the carburetor. Be sure to write down in your notebook all the important facts you come across.
[144]
6: Fuel injection and LPG fuel
systems
IN PREVIOUS chapters, we have discussed carburetor fuel systems; these are the most widely used automotive fuel systems. However, there are other fuel systems; these are considered in this chapter. They include the fuel-injection system which has several variations and the LPG fuel system. Fuel-injection systems are used on
both gasoline engines and diesel engines.
Some automobiles are now
equipped with a fuel-injection system instead of a carburetor fuel
§93. Gasoline fuel-injection systems
FIG. 6-1. Simplified view showing
method of injecting fuel directly into
combustion chamber of engine.
FIG. 6-2. Simplified view showing
method of injecting fuel into intake
manifold just back of the intake valve.
system. There are two basic types of fuel injection systems. In one,
the fuel is injected directly into the combustion chamber (Fig. 6-1).
In the other, the fuel is injected into the intake port behind the in[145J
Automotive Fuel, Lubricating, and Cooling Systems
§94
take valve (Fig. 6-2). The latter system is simpler and is the one
generally used in automotive applications. It is described in the following paragraphs.
§94. Ramjet fuel-injection system The major components of this system are shown in Fig. 6-3. It consists essentially of a special intake
manifold, an air meter, and a fuel meter. The air meter controls the
Bow of air through the intake manifold to the engine cylinders. The
fuel meter controls the Bow of fuel to the injection nozzles in the intake manifold. The system is simple; linkage from the accelerator
FUEl
MfTE~
FIG. 6-3. Basic components of fuel-injection system. (Chevrolet Motor Division
of General Motors Corporation)
pedal actuates a throttle valve in the air meter; more air is admitted
when more engine power is desired. The fuel meter operates to provide varying amounts of fuel; it supplies more fuel as more air is
admitted.
Other mechanisms enrich the mixture for acceleration, warm-up,
hill climbing, and so on. Figure 6-4 is a sectional drawing of the
complete system.
§95. Air intake The air intake of the system is shown in Fig. 6-5.
The amount of air that enters is controlled by the throttle valve
(see Fig. 6i 4) which is located in the throat of the air meter. The
throttle v~l
is connected by linkage to the acclerator pedal, just
[146]
\.
§95
Fuel Injection and LPG Fuel Systems
FAST START SOLENOID
FUEL-ENRICHMENT DIAPHRAGM
.. IR
c"":;"'-_ _ _
COMBUSTION CH ..MBERS -_;,~"
6-4. Sectional view of complete fuel-injection system. (Chevrolet Motor
Division of General Motors Corporation)
FIG.
VACUUM TUBE
AIR
CLEANER
COMBUSTION CHAMBER
FIG. 6-5. Air intake of fuel-injection system. (Chevrolet Motor Division of General Motors Corporation)
L147]
Automotive Fuel, Lubricating, and Cooling Systems
§96
as the throttle valve in the carburetor. As the throttle valve is
opened, more air flows into the intake manifolds and engine cylinders. A vacuum tube, connected at a venturi at the air cleaner
end of the air meter, "senses" the amount of air entering. When only
a little air is entering, then there is only a little vacuum applied to
the vacuum tube. But when considerable air enters, then more
vacuum develops at the venturi and is applied to the tube. This
varying vacuum is used to control the amount of fuel the fuel meter
delivers to the injection nozzles in the intake manifold.
§96. Fuel intake The essential parts of the fuel-intake system are
shown in Fig. 6-6. The regular engine fuel pump sends fuel into a
RETURN TO
RESERVOIR
FIG. 6-6 , Fuel intake and injection of fuel-injection system . (Chevrolet Motor
Division of General Motors Corp01'ation)
reservoir in the fuel-meter hOUSing. There, a high-pressure fuel
pump sends fuel past a ball check and into a metering chamber.
From herE\, It can go either to the injection nozzles or back to the
[148]
!\
\
\
Fuel Injection and LPG Fuel Systems
§96
reservoir. The direction it Hows depends upon the position of the
plunger. Two positions of the plunger are shown in Fig. 6-7. To the
left, the plunger is lowered so as to cause delivery of more fuel to
the injection nozzles. This action results when the throttle is opened
fairly wide and a high vacuum is being applied to the vacuum tube
and to the vacuum diaphragm. The diaphragm lifts, raising the
lever so that the lever pivots around the movable pivot, pushing
down on the plunger. To the right in Fig. 6-7, the condition during
low air How is shown. Here, there is a low vacuum and the vacuum
diaphragm has relaxed and permitted the lever to fall. Therefore,
the plunger pushes up farther and less fuel Hows to the nozzles.
HIGH ,AIR FLOW CAllS FOR HIGH FUEL FLOW.
FUEL LINE
L..J_---'--'(TO NozzLES)
lOW AIR FLOW CAllS FOR lOW FUEL FLOW.
(TO HOULESI
6-7. Method of controlling amount of fuel delivered to injection nozzles.
( Chevrolet Motor Division of General Motors Corporation)
FIG.
1. Acceleration. The movable pivot enters into the control of the
fuel How during both acceleration and during cold starting. Figure
6-8 shows the controls used to obtain fuel enrichment during acceleration. An enrichment vacuum tube is connected between the
air meter and a fuel-enrichment diaphragm. When the throttle is
opened wide for fast acceleration, the vacuum in the air meter
drops. This allows the fuel-enrichment diaphragm to relax so the
spring pushes the diaphragm to the left (in Fig. 6-8). Through
linkage, this pushes the movable pivot to the left and it assumes the
position shown in Fig. 6-9. Now, with the pivot to the left, the
plunger is forced down into the position in which it is shown to the
left in Fig. 6-7. With more fuel Howing to the injection nozzles, a
richer mixture and improved acceleration are attained.
[149]
Automotive Fuel, Lubricating, and Cooling Systems
§96
2. Cold starting. An electrically h.e ated choke enters into the
action to provide control of fuel intake during cold starting (Fig.
6-9). Note that this illustration shows the electric choke cut into the
fuel-enrichment vacuum line. On cold starts, vacuum in the choke
housing hom the fuel-enrichment vacuum line lifts a check ball and
cuts off the vacuum to the enrichment diaphragm. Then the diaphragm relaxes and shifts the movable pivot to the left (in Fig. 6-9).
In this position, the lever forces the plunger down so that more fuel
FUEL ENRICHMENT DIAPHRAGM
FIG . 6-8. Mechanisms for shifting movable pivot to enrich mixture for good
performance on acceleration. (Chevrolet Motor Division of General Motors
Corporation)
is delivered. As the thermostat in the choke is heated, it relaxes and
allows vacuum to pull the piston downward. As the piston moves
down, it pushes the check ball off its seat so that vacuum is permitted to pass through the choke and to actuate the fuel-enrichment
diaphragm. This action causes the movable plunger to swing back
into the warm-engine position so that the mixture is leaned out to
that which is required for warm-engine operation.
The electric choke also controls a fast-idle cam that holds the
throttle val~
slightly opened for better idling when the engine is
cold.
\
[150]
\
Fuel Injection and LPG Fuel Systems
§97
3. Other features. To provide adequate fuel quickly during engine cranking, a fast-start solenoid (see Fig. 6-4) is included in the
fuel-meter assembly. This solenoid is actuated as the cranking motor
operates ( it is connected to the control circuit). The solenoid then
operates linkage to the ball check below the plunger in the fuel
meter to push the ball check off its seat so that the fuel pump can
instantly deliver fuel to the injection nozzles. A fuel cut-off diaphragm (Fig. 6-4) comes into operation when coasting down hill or
decelerating to shut off fuel How. This diaphragm is connected by a
tube to the air meter. When a high vacuum is produced in the air
PLUNGER
I, ·
6-9. Choke system for cold startu>g. (Chevrolet Motor Division of General
Motors COt'poration)
FIG.
meter by deceleration, the diaphragm is actuated and the fuel is
shut off.
§97. Diesel-engine operation Diesel engines use a fuel-injection system that injects fuel into the combustion chamber after the piston
has completed its compression stroke. Air alone is compressed; the
pressure goes up so high that the air temperatme may reach lOOO°F.
Then, when the fuel is injected, it is ignited by the temperature of
the air. Diesel engines are sometimes called compression-ignition
engines for this reason. No ignition system, such as is used in automotive engines, is required.
§98. Diesel-engine fuel-injection system The diesel-engine fuel-injection system must have two special characteristics that the fuelinjection system already described does not require. First, the in[151]
Automotive Fuel, Lubricating, and Cooling Systems
§98
jection must be intermittent; a fuel nozzle must deliver fuel only at
the time the piston is reaching top dead center on the compression
stroke. Secondly, the fuel must be delivered at very high pressure
since it is being injected into air that has been compressed to several hundred pounds per square inch of pressure. In addition to this,
the amount of fuel delivered must vary with varying operating conditions so that more fuel is injected when more power is required.
,._------- ----I
_.-- - --------_ ...........
I
,,
I
I
~'"
_______ _ __ ..: _ _ __________________ _ ____ . __ JI
FIG. 6-10. General Motors dieselengine fuel system. (Detroit Diesel
Engine Division of General Motors
Corporation)
1. Fuel tank
2. Primary filter
3. Fuel pump
4. Secondary filter
5. Lower (inlet) fuel manifold
6. Inlet tube to injector
7. Injector
8. Outlet tube from injector
9. Upper (outlet) fuel manifold
10.
11.
12. Fuel lines
13.
14.
Figure 6-10 illustrates one type of diesel-engine fuel system. The
fuel is delivered by a high-pressure fuel pump through a filter to the
fuel injectors. The fuel injectors are mounted above the engine
cylinders as shown in Fig. 6-11 and are actuated by a camshaft,
push rod, and rocker arm. When the cam lifts the push rod, the
rocker arm forces a plunger in the injector to move down. The
plunger has a helix cut in it as shown in Fig. 6-12. When the helix
is not opposite either of the ports, it is effectively delivering fuel on
its downwartl. stroke, as shown. The effective stroke, and thus the
amount of ,ftwl delivered, can be varied by rotating the plunger.
\
'.
\
\
\
Fuel Injection and LPG Fuel Systen:s
§99
-,,; .
. 3 --
FIG. 6-1l. MOW1ting of fuel injector above the engine
Engine Division of General Motors Corporation)
l. Camshaft
9. Injector rocker arm
2. Cam follower
10. Ball stud and seat
3. Following spring
11. Injector assembly
4. Injector clamp
12. Control tube
5. Push rod
13. Rack-conb'ol lever
14. Injector control rack
6. Lock nut
15. Copper tube
7. Clevis
8. Rocker-arm shaft
16. Cylinder head
cylinder. (Detroit Diesel
17. Cylinder liner
18. Cylinder-head
gasket
19. Balancer shaft
20. Cylinder block
2l. Copper-tube sealing
ring
This eHect is shown in Fig. 6-13. The pltmger is rotated by means
of a rack and gear that is linked to the accelerator pedal or control.
Liquefied petroleum gas,
or LPG, is a fuel that is liquid only under pressure. 1 When the
pressure on LPG is reduced, it vaporizes. Thus, the first need in an
§99. Liquefied petroleum gas fuel systems
1 Composition and characteristics of LPG are discussed in Chap. 7, "Automotiveengine Fuels."
[1531
Automotive Fuel, Lubricating, and Cooling Systems
§99
UPPER
PORT
,
I
LOWER
PORT
,,/"
CENTRAL
PASSAGE I
-
TOP
OF
STROKE
BOTTOM
OF
END OF
INJECTION
STROKE
START OF
INJECTION
STROKE
STROKE
-
.
FIG. 6-12. Operation of the plunger during the injection stroke. (Detroit Diesel
Engine Div ision of General Motors Corporation)
EFFECTIVE
EFFECTIVE
EFFECTIVE
STROKE
STROKE
STROKE
I
.I
UPPER
PORT
I
I
~-r
LOWER
PORT
IDLING
NO
INJECTION
LOAD
HALF
FULL
LOAD
LOAD
6-1S. Positions of plunger to secure various amounts of fuel injection.
(Detroit Diesel Engine Division of General Motors Corporation)
FIG.
LPG fuel system is a special pressure fuel tank that will keep the
fuel under pressure until it is used. The pressure requirement also
means that the storage tanks at the fueling pOints must be of special
construction. In addition, LPG must be transported from the refineries 0 oil fields in special pressure-tank cars or trucks. For
[154}
\
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Fuel Injection and LPG Fuel Systems
§99
these reasons, engineers state that LPG is satisfactory as an automotive fuel only in fleet operations (trucks and busses), where
there are enough vehicles to make it economically reasonable to
invest in the special high-pressure storage equipment required.
Despite the greater cost of transporting and storing LPG (because of the special handling that pressure tanks require), its use
is increasing in fleet operations. Some studies indicate that this increased cost is at least balanced by reduced operating and maintenance costs. Advantages claimed for LPG include:
1. Higher compression ratios can be used, with resulting increased engine power output.
2. No crankcase dilution due to failure of fuel to vaporize (LPG
enters intake manifold completely vaporized).
3. No washing of oil from cylinder walls by unvaporized fuel
and thus no wear from loss of lubrication.
4. Absence of deposits on valves and in combustion chamber.
A typical fuel system for LPG is shown in Fig. 6-14. Notice that
it does not use a fuel pump. The pressure in the fuel tank is more
~
LPG liquid
ill
LPG vapor
~
Engine cooling water
IZSI Air-gas
FIG. 6-14. Typical fuel system for LPG.
mixture
than sufficient to assure a flow of fuel to the carburetor. Actually,
two pressure reducers, or regulators, are placed in the line so that
the pressure is brought down to slightly below atmospheric before
the fuel enters the carburetor.
1. The fuel tank is of heavy construction, capable of containing
[155]
Automotive Fuel, Lubricating, and Cooling Systems
§99
pressures of at least 250 psi. Special filling and relief valves are
required. The tank must not be filled more than 80 percent full,
since there must be expansion room to take care of temperature
variations. Many tanks are designed to use a special pressure nozzle
that locks on the filling valve. The locking action opens the valve so
that fuel can be pumped into the tank. At the same time, it closes
a second valve to an inner expansion tank in the fuel tank. This
inner expansion tank, which is 20 percent of the size of the fuel
tank, provides the necessary expansion room for the fuel. Detaching
the filling nozzle from the tank closes the filling valve and opens
the valve to the expansion tank. Fuel can now expand into the expansion tank if temperature increases.
2. The shutoff valve provides a means of turning off the fuel
for maintenance work. The filter removes from the liquid fuel any
dirt that might have accumulated in it.
3. The liquid fuel is forced from the tank through the tube
to the high-pressure regulator by the pressure in the tank. This
pressure may run anywhere from 225 down to 20 psi. The highpressure regulator reduces this pressure to somewhere between 5
and 15 psi (depending on the type of equipment). The LPG thus
leaves the high-pressure regulator in a semiliquid condition, partly
liquid, partly vapor. It then enters a vaporizer. The vaporizer consists essentially of an inner tank through which the fuel passes, and
an outer tank through which hot water from the engine cooling
system passes. The water adds heat to the fuel, assuring more complete vaporization. The vaporized LPG then passes through the
low-pressure regulator and is reduced in pressure to a value slightly
below atmospheric pressure. It is now ready to pass through the
carburetor. Pressure must be reduced to slightly below atmospheric
so that no fuel will flow until the engine is turning over and drawing air in through the carburetor. This action produces a vacuum
in the carburetor venturi which causes fuel delivery in the carburetor.
4. The carburetor is essentially a mixing valve. It contains a
throttle valve, an air horn, a venturi, and starting, idling, partthrottle, and full-throttle circuits. No provision for atomizing or
vaporizing the fuel is needed, as with gasoline fuel systems, since
the LPG enters the carburetor as a vapor. It passes through a gas
orifice into the air stream in the air horn, and the mixture then
[156]
\
\
:\
Fuel In;ection and LPG Fuel Systems
§99
passes through the intake manifold to the engine cylinders. For
part-throttle operation, many carburetors include a vacuum-operated economizer valve that reduces the size of the gas orifice when
the throttle is partly opened and there is a vacuum in the intake
manifold. When the throttle is opened wide and the vacuum is reduced, the economizer valve is released so that it opens and increases the size of the gas orifice. More fuel is thus delivered, and
the mixture is enriched for full-throttle operation.
CHAPTER CHECKUP
NOTE: Since the following is a chapter review test, you should review
the chapter before taking the test.
You may not run into fuel-injection or LPG fuel systems very often, but
when you do, you will want to be able to deal intelligently with them.
Thus, you will want to remember the important facts discussed in the
chapter just completed. The following questions will give you a chance
to review the material you have just covered on these fuel systems. Write
down the answers in your notebook.
Completing the Sentences
The sentences below are incomplete. After each sentence there are
several words or phrases, only one of which will correctly complete the
sentence. Write each sentence down in your notebook, selecting the
proper word or phrase to complete it correctly.
l. In the diesel engine, fuel oil is injected into the cylinder toward the
2.
3.
4.
5.
6.
7.
end of the
intake stroke
compression stroke
pmver
stroke
exhaust stroke
In the diesel engine, fuel oil is injected into the cylinder at
low
60 psi
pressure
high pressure
In the General Motors diesel fuel system the fuel pump delivers the
fuel oil through a filter to the carburetor ignition distributor
injectors
In the General Motors diesel fuel system the injectors are operated
through rocker arms from a
crankshaft
camshaft
gear shaft
In the General Motors diesel system the effective pressure strokes of
fuel
the plungers in the injectors are regulated by means of a
pump
control rack
camshaft
check valve
The LPG fuel system does not use a
carburetor
fuel tank
fuel pump
LPG must be stored as a
vapor
liquid
gas
[157]
Fuel Iniection and LPG Fuel Systems
8. With LPG fuel, compression ratio of the engine can be
creased
reduced
in-
eliminated
Purpose and Operation of Components
In the following, you are asked to write down the purpose and operation of certain components of diesel and LPG fuel systems. Obviously,
only one diesel fuel system has been covered in the chapter. There are
many. It is suggested that you also attempt to learn about other diesel
fuel systems as well as LPG fuel systems. You can write your answers to
the questions below, as well as what you might learn about other diesel
fuel systems and LPG fuel systems, in your notebook.
1.
2.
3.
4.
List some of the differences between diesel and gasoline engines.
Explain how an automotive fuel-injection system operates.
Explain how a typical diesel fuel-injection system operates.
Explain how the automotive fuel-injection system varies the amount
O.f fuel injected to' suit operating requirements of the engine.
5. What are the advantages claimed for LPG as a fuel?
6. What is the purpose of the pressure regulators in the LPG fuel
system?
7. Explain how the LPG fuel system operates.
SUGGESTIONS FOR FURTHER STUDY
If you wish to learn more about diesel-engine fuel systems, you can
refer to various books that have been written on diesel engines, as well as
to the diesel-engine manufacturers' servicing and operating manuals. Late
information on developments in LPG fuel systems can be found in automotive trade magazines and in publications of LPG producers and
manufacturers of engines designed to use LPG. You will find it helpful
for you to write down in your notebook any facts that you might learn
about such fuel systems. Not only does this fix the information in your
mind, but it also makes your notebook a valuable reference you can use
to refresh your memory.
\
[158]
'\
\\
\
\
7: Automotive-engine fuels
THE PURPOSE of this chapter is to discuss the origin and char,
acteristics of various automotive-engine fuels, including gasoline,
LPG (liquefied petroleum gas), and diesel-engine fuel oi1. In addition, the effect of the different characteristics of gasoline on
engine operation are discussed.
§100. Automotive-engine fuels The American passenger-car engine
uses gasoline as fuel. Other types of engines, for example, those
used in tractors, trucks, and busses, may use kerosene, distillate
alcohol, fuel oil, or LPG. Since this book deals primarily with
gasoline-engine fuel systems, only gasoline will be discussed in
detail. However, diesel fuel oil and LPG are covered in special
sections at the end of this chapter. Diesel-engine and LPG fuel
systems are described in Chap. 6, "Diesel and LPG Fuel Systems."
§101. Gasoline Gasoline appears to be a simple compound when
you first examine it. It is a clear or colored liquid that evaporates
quickly from a flat pan and bums violently in the open air. Gasoline is not, however, a simple compound. It is a complex mixture
of several compounds. It is a blend of i number of different basic
fuels, each of which contributes its own characteristics to the
mixture.
Gasoline is a hydrocarbon, since it is made up of hydrogen
and carbon compounds. We have already noted that, when gasoline bums, the hydrogen and carbon atoms separate from each
other and combine with oxygen atoms (see §27). It is this com·
bustion process that produces the high pressure in the cylinder
that forces the piston down so that the engine produces power.
§102. Origin of gasoline Gasoline, diesel fuel oil, LPG, and many
other compounds are obtained from petroleum, or crude oil. No
one knows exactly how petroleum originated. It is found in "pools')
under the ground, and there is evidence that it was formed over
[1591
§103
Automotive Fuel, Lubricating, and Cooling Systems
a space of many millions of years from animal or vegetable sources.
The petroleum usually is under considerable pressure; when a well
is drilled down to a pool or reservoir, the petroleum gushes up out
of the earth.
Petroleum is a very intricate mixture of many compounds. The
oil refinery separates the petroleum into various substances. It alters
many of the original compounds and forms new compounds in the
refining process. From the refinery come many types and grades
of lubricating oil, fuel oil of various types for diesel engine, heating,
and so forth, gasoline of many grades and types, kerosene, LPG,
and so on.
As mentioned above, gasoline is blended from a number of different basic hydrocarbons, each with its own set of characteristics.
By blending various basic fuels, a gasoline is obtained that will
provide satisfactory engine operation under the many different
operating conditions that the engine will meet. Factors that must
be considered in blending gasoline include volatility, antiknock
value, and freedom from harmful chemicals and gum. These factors
are discussed in detail in following sections.
§103. Volatility Volatility refers to the ease with which gasoline
and other liquids vaporize. The volatility of a simple compound like
water or alcohol is determined by increasing its temperahlre until
it boils, or vaporizes. A liquid that vaporizes at a relatively low
temperature has a high volatility; it is highly volatile. If its boiling
point is high, it has a low volatility. A certain heavy oil, for example, has a low volatility since it will not boil until it reaches a
temperature of over 600°F. Water is relatively volatile since it
boils at 212°F (at atmospheric pressure). Gasoline is still more
volatile.
It is also true that a highly volatile substance will evaporate
much faster at a low temperature than a substance with a low
volatility. Thus, at room temperature, alcohol and gasoline will
evaporate more rapidly than water.
Gasoline is blended from different hydrocarbon compounds that
have different volatilities or boiling pOints. Some compounds of
gasoline will therefore evaporate more readily at low temperatures
than others. This combination assures satisfactory operation under
the various operating conditions the engine meets, as follows.
[160]
Automotive-engine Fuels
§103
1. Easy starting. For easy starting with a cold engine, gasoline
must be highly volatile so that it will vaporize readily as it passes
through the carburetor even when air and fuel temperatures are
low. Thus, a certain percentage of the gasoline must be volatile
enough to permit easy starting. In winter the percentage of highvolatility gasoline is increased for good cold-weather starting. Also,
the percentage of high-volatility gasoline is varied for the different
parts of the country; the percentage is higher in the colder Northern states.
2. Freedom from vapor lock. If the gasoline is too volatile, heat
from the engine will cause it to vaporize in the fuel lines and fuel
pump. This action results in gas pockets, or vapor locks, that prevent normal fuel-pump action. When gas pockets exist, the increasing and decreasing pressure in the fuel line (due to fuelpump action) simply causes the pockets to contract and expand.
Thus, little or no fuel is pumped from the fuel tank to the carburetor. The engine then loses power or completely stalls from
fuel starvation. To prevent vapor locks, the percentage of highly
volatile gasoline must be kept relatively low. Thus, it can be seen
that the requirements for easy starting and requirements for freedom from vapor lock are in opposition. That is, there must be
enough high-volatility gasoline for easy starting, but not so much
as to cause vapor lock.
3. Quick warm-up. The speed with which the engine will warm
up depends in part on the percentage of gasoline that will vaporize
immediately after the engine is started (and thus contribute to
engine operation). Volatility for this purpose does not have to be
quite so high as for easy starting. This is because immediately after
starting, the air speed through the carburetor is greater, and
turbulence in the manifold and cylinder during intake and compression helps to vaporize the gasoline.
4. Smooth acceleration. When the throttle is opened for acceleration, there is a sudden increase of air rushing through the carburetor into the engine cylinder. At the same time, the accelerator
pump delivers an extra amount of gasoline. If the gasoline does not
vaporize quickly during this interval, a large mass of air will reach
the cylinders without carrying its proper proportion of gasoline
vapor. The mixture entering the cylinders will be too lean for good
combustion, and the engine will hesitate or stutter. Immediately
[161]
§103
Automotive Fuel, Lubricating, and Cooling Systems
afterward, as the gasoline metered out by the accelerator pump
begins to vaporize, the mixture reaching the cylinders will become
too rich. This again produces poor combustion and a logy engine.
The result is uneven and inferior acceleration. A sufficient percentage of the gasoline must be volatile enough to prevent this
condition. But on the other hand, if too large a percentage of the
gasoline is highly volatile, there will be an overrich mixture on
acceleration. This would cause the engine to "roll" or "load up,"
causing poor acceleration.
5. Good economy. For good fuel economy, or maximum miles per
gallon, the fuel must have a high heat, or energy, content and
relatively low volatility. High over-all volatility tends to reduce
economy, since the mixture may become overrich under many
conditions of operation. On the other hand, the lower-volatility
fuels tend to burn more efficiently, providing better fuel economy.
But the lower-volatility gasolines increase starting difficulty, reduce
speed of warm-up, and do not give good acceleration. Thus, only a
limited percentage of the gasoline can be of low volatility.
6. Freedom from cmnkcase dilution. When gasoline is not sufficiently volatile, some of it will enter the cylinder in liquid form,
as tiny unevaporated droplets. These droplets spray on the cylinder
walls, washing off the film of lubricating oil. Removing the lubricating-oil film in this manner increases the rate at which the
cylinder wall, piston rings, and piston will wear. Furthermore, the
liqUid gasoline passes the piston rings and enters the oil pan, or
crankcase. The lubricating oil is thus diluted by the gasoline, and
it loses some of its lubricating ability. This means that all moving
engine parts will wear more rapidly. After the engine has operated
for a while and has thoroughly warmed up, this liquid gasoline in
the crankcase begins to vaporize and is removed by the crankcase
ventilating system (described in §223). To avoid damage to the
engine before it warms up, the gasoline must be sufficiently volatile
to avoid crankcase dilution.
7. The volatility blend. It is obvious from the above discussion
that no one volatility would satisfy all engine operating requirements. On the one hand, the fuel must be of high volatility for easy
starting and acceleration. But it must also be of low volatility to
give good fuel economy and combat vapor lock. Thus, gasoline
must be blended from various amounts of fuels having different
[162]
\
Automotive-engine Fuels
§10S
volatilities. Such a gasoline then satisfies the various operating
requirements.
§104.
Antiknock value During normal combustion in the engine
cylinder, an even increase of pressure occurs. But if the fuel burns
too rapidly, or "explodes," there is a sudden and sharp pressure increase. This sudden pressure increase produces a rapping or knocking noise that sounds almost as though the piston head had been
struck with a hard hammer blow. Actually, the sudden pressure increase does impose a sudden heavy load on the piston that is
almost like a hammer blow. This can be very damaging to the
engine, wearing moving parts rapidly and perhaps even causing
parts to break. Furthermore, the energy in the gasoline is wasted
since the sudden pressure increase does not contribute much toward
the production of power.
It has been found that some types of gasoline burn very rapidly
in engine cylinders and thus knock very badly. Other types of fuel
burn more slowly and thus do not knock. Also, certain chemicals
have been found which, when added to the gasoline, will slow
down the rate of burning so that knocking is eliminated. Gasoline is
rated according to how easily it will knock, that is, by its antiknock value. The actual rating is by octane number. This term, and
the theory of knocking, are discussed in following sections.
§105.
Before we discuss the antiknock value of
gasoline further, let us talk about engine compression ratio since
this is very directly connected to knocking. On the compression
stroke, the piston moves up and compresses the air-fuel mixture in
the cylinder. The amount that the mixture is compressed is determined by the engine design; that is, by one specific characteristic
of the engine called the compression ratio. The compression ratio
is the ratio of the volume in the cylinder with the piston at BDC
(bottom dead center) to the volume with the piston at TDC (top
dead center). This is shown in Fig. 7-1. For example, let us assume
that the volume in the cylinder with the piston at BDC (A in
Fig. 7-1) is 40 cubic inches and the volume at TDC is 5 cubic
inches. In other words, as the piston moves up from BDC to TDC,
it compresses the air-fuel mixture from 40 cubic inches to 5 cubic
inches. The proportion, or ratio, of compression is 40 to 5, or 8 to
1 (written 8: 1). In other words, the compression ratio is 8: 1.
[163]
Compression ratio
Automotive Fuel, Lubricating, and Cooling Systems
§106
The higher the compression ratio, the more the air-fuel mixture
is "squeezed" on the compression stroke. Thus, there is a higher
initial pressure at the beginning of the power stroke. This means, in
turn, that there is more pressure on the piston as combustion begins,
which brings us to the basic advantage of higher compression ratios.
With more pressure on the piston during the combustion stroke,
more power will result. Therefore, increasing the compression
ratio increases engine output. That is the reason engine designers
and manufacturers are producing engines of higher and higher
compression ratios. By redesigning the engine to step up compression ratio, they get an engine with a higher horsepower output
without a comparable increase in size. In fact, modern high-com"8
11
(@
FIG. 7-1. Compression ratio is
'-~
volume in cylinder with piston
at BDC divided by volume with
piston at TDC, or A divided
by B.
'-
Piston at
Piston at
BOC
TDC
pression engines weigh much less and are much more powerful than
earlier engines.
The increase of compression ratio has brought about certain
difficulties, however, since a high-compression engine has a greater
tendency to knock. Thus, it has been necessary to find fuels that
resist knocking for these higher-compression engines. A great deal
of research, both in the laboratory and on testing grounds, has
been done to find these antiknock fuels.
§106. Heat of compression To understand why knocking occurs, it
is first necessary to understand what happens to any gas when it is
compressed. We have already noted that in the diesel engine, when
the air is compressed to one-fifteenth of its original volume (compression ratio 15: 1), the air temperature increases to about lOOO°F
( §93 ). The, more a gas is compressed, the higher its temperature
will go. This temperature rise is called heat of compression.
[164]
Automotive-engine Fuels
§107. Cause of knocking
§107
During normal burning of fuel in the
combustion chamber, the spark at the spark plug starts the burning
process. A wall of flame spreads out in all directions from the spark,
almost like a rubber balloon being blown up. The wall of flame
travels rapidly outward through the compressed mixture in the combustion chamber until all the charge is burned. The speed with
which the flame spreads is called the rate of flame propagation. The
movement of the flame wall through the combustion chamber
during normal combustion is shown in the row of pictures to the
left in Fig. 7-2. During combustion, the pressure in the combustion
chamber increases to several hundred pounds per square inch
(psi). It may exceed 700 psi in the modern high-compression
engine.
If the flame travels too rapidly through the mixture (rate of
flame propagation is too high), the pressure will increase too
rapidly and will go too high. The effect will be as shown to the
right in Fig. 7-2. The rapid increase of pressure, and excessive
pressure, will cause the last part of the charge to detonate, or explode, with hammerlike suddenness. The effect is almost the same
as if you had suddenly struck the piston head with a heavy hammer
blow. In fact, it sounds as though this had happened. The sudden
explosion of the last part of the charge hammers on the piston head,
and imposes a heavy shock load on the piston, connecting rod,
crankshaft, and bearings. With very severe knocking, engine parts
will actually be broken.
Let's take a closer look at knocking. We have mentioned that
knocking results from an excessively rapid increase in pressure. This
rapid pressure increase highly compresses the remaining unburned
charge. Heat of compression (§106) then raises the temperature of
the unburned charge. Detonation, or knocking, occurs when the
temperature has gone up so high that the remaining unburned
charge explodes. To sum up, the process is about as follows. The
spark occurs and combustion starts. The charge starts burning too
rapidly (rate of flame propagation too high). Pressures go up excessively, developing excessive heat of compression in the unburned charge. The heat of compression then sets off the remainder
of the charge.
As compression ratios of engines have gone up, so also has the
tendency of the engines to knock. With higher compression ratios,
[165]
Automotive Fuel, Lubricating, and Cooling Systems
§107
7-2. Normal combustion without knocking is shown in the vertical row to
the left. The fuel charge burns smoothly from beginning to end, providing an
even, powerful thrust to the piston. Knocking is shown in the vertical row to
the right. The last part of the fuel explodes, or burns almost instantaneously,
to produce detonation, or knocking. (General Motors Corporation)
FIG.
\\
Automotive-engine Fuels
§108
the mixture, at TDC, is more highly compressed and is at a higher
initial temperature. With higher initial pressure and temperature,
the temperature at which detonation occurs is sooner reached.
Thus, high-compression engines have a greater tendency to knock.
However, special fuels have been developed for use in such engines
as explained below. These special fuels have a greater resistance to
being set off suddenly by heat of compression. They are less apt to
explode suddenly, and they depend for their ignition upon the
wall of flame traveling through the air-fuel mixture.
§108. Measuring antiknock values of fuels Several methods of testing fuels to determine their tendency to knock in engines have been
developed. Some fuels knock rather easily; others have a high resistance to knock (that is, have a high antiknock rating). Actual
rating of a fuel for its antiknock value is made in terms of octane
rating. A high-octane gasoline is highly resistant to knock, a lowoctane gasoline knocks rather easily. There is a fuel called isooctane that is extremely resistant to knocking; it is given an octane
rating of 100. Another fuel, called heptane, knocks very easily; it
is given an octane rating of zero. A mixture of half iso-octane and
half heptane (by volume) would have a 50-octane rating. A mixture
of 75 percent iso-octane and 25 percent heptane would have a
rating of 75 octane.
Actually, iso-octane and heptane are reference fuels, used only
to rate unknown fuels. One rating procedure makes use of a test
engine (Fig. 7-3) so built that its compression ratio can be varied.
A fuel to be rated is used to run the engine, and the compression
ratio is increased until a certain intensity of knocking is obtained.
Then, reference fuels of varying proportions of iso-octane and
heptane are used to run the engine. The octane rating of the reference fuel is decreased (by using smaller percentages of iso-octane)
until the same intensity of knocking results as was obtained with
the fuel to be rated. Then, the fuel being rated is given the same
octane number as the reference fuel since both produce the same
amount of knocking. If the reference fuel has 68 percent iso-octane,
for example, then it and the fuel being tested are considered to have
the same 68-octane rating.
1. Laboratory-test method. The laboratory-test method of measuring octane rating of a fuel has already been described. Essentially,
[167]
Automotive Fuel, Lubricating, and Cooling Systems
§108
the test engine is operated at a certain speed, with a certain ignition
spark advance, and the compression ratio is varied until the test
fuel causes knocking. Note that all conditions except compression
ratio are kept constant through the test. This differs from actual
over-the-road operation, where the compression ratio stays the
FIG. 7-3. Special engine for testing knock characteristics, or octane ratings,
of fuels. (Waukesha Motor Company)
same (it's built into the engine) but most other conditions change
(including speed, spark advance, temperature, carburetion, fuel
distribution to cylinders, and so forth). This difference between
laboratory, test procedure and actual operating conditions has been
apparent ill the highway performance of laboratory-rated fuels. A
[168]
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A.utomotive-engine Fuels
§108
fuel that knocks in one engine may not knock in another. A fuel
that knocks at low speed may not knock at high speed. Another fuel
may knock at high speed but not at low speed. However, despite
the fact that the laboratory rating cannot pin-point octane rating
of a fuel for all kinds of performance, it is still of value since it
does give comparative ratings between different fuels.
2. Road-test methods. In order to determine more accurately
how a fuel will act in normal highway operation, a number of road
octane-rating tests have been developed. One of these, the Cooperative Fuel Research Uniontown road test (called the CFR Uniontown road test), rates fuels for knock intensity at Wide-open throttle
25
}--
",20
V
Q)
"0
ico
15
§!
"0
o
"'"'- 10
5
1/
o
o
ro
o
a.
V'>
L
v
w
~
/'"I--
.L
~
~
w ro
00
Car speed, mph
FIG. 7-4. Borderline knock curve. The fuel being tested will knock if the ignition
spark is advanced to any value above the curve at any speed.
at various speeds. Octane is assigned by comparing knocking of
the fuel being tested to reference fuels (iso-octane and heptane
mixtures) of known octane values.
Another method, the borderline knock test, rates the fuel at
various speeds and is considered to give much more information on
fuel performance. This test is made by running the car at various
speeds and then determining the amount of ignition spark advance
the fuel can tolerate at each speed without knocking. If the spark
is advanced too much at any speed, knocking will occur. Thus, the
test results give us a curve that shows, at every speed, the knock
characteristics of the fuel being tested (Fig. 7-4). Note, in Fig.
7-4, that the fuel tested permits an increasing spark advance with
increasing speed. Any advance above the curved line causes knock.
To show how different fuels might act in the borderline knock
[169]
§108
Automotive Fuel, Lubricating, and Cooling Systems
test, see Fig. 7-5. This shows the curves of two fuels, A and B.
Curve C is the amount of spark advance the distributor provides on
the engine used in the test. If, at any particular speed, the distributor advances the spark more than the fuel can tolerate, the
fuel will knock. Thus, at low speed, fuel A will knock since the
spark advance is more than the fuel can tolerate (that is, curve
C is above curve A at low speed). On the other hand, fuel A will
not knock at high speed since the spark advance is not up to the
amount the fuel can tolerate at high speed. But fuel B gives a different story. It will not knock at low speed, but does knock at
25
",20
'"
-0
",-
g 15
~ c ..
~
-0
o
~
-'"L 10
~
o
a.
(f">
5
o
o
10
/
20
~
k.
L
~ r-----
f.---
/'
v
30
40
50
Car speed, mph
60
70
80
FIG. 7-5. Comparison of borderline knock curves of two fuels, A and B. Curve C
is the spark advance actually provided by the ignition distributor on the engine.
high speed. These curves, which apply only to fuels A and B
emphaSize the fact that different fuels act differently at different
speeds and in different engines.
CHECK YOUR PROGRESS
Progress Quiz 5
Here is your progress quiz for the first half of the chapter. You will note
that these checkups are included only in the longer chapters. They are
designed to give you a breathing spell and allow you to stop to find out
how well you are learning the essential details of the fuel system that you
are studying. Whenever you are reading a book, it is always desirable to
stop every few pages to sum up what you have been reading. In this way,
you review the material, and it will be much easier to remember. The
progress quizzes throughout the book, as well as the chapter checkups,
give you tl,:te' chance to make these periodic reviews.
[170]
\
~.
.\
\
\
\
\.
Automotive-engine Fuels
Completing the Sentences
The sentences below are incomplete. After each sentence there are
several words or phrases, only one of which will correctly complete the
sentence. Write each sentence down in your notebook, selecting the
proper word or phrase to complete it correctly.
coal, coke,
and oil
gasoline, LPG, and oil
alcohol, gasoline, and LPG
The ease with which a liquid vaporizes is called its
vaporability
volatility
octane rating
Vapor lock is most apt to occur in the
fuel lines or pump
fuel pump or tank
carburetor or tank
tank or gauge line
The possibility of vapor lock increases as
volatility decreases
volatility increases octane rating increases
For good fuel economy the gasoline must have a high energy content
and relatively
low volatility
high volatility
high octane
To avoid crankcase dilution and washing of the cylinder walls, the
gasoline must have a relatively
low volatility
high volatility
high octane
The antiknock value of gasoline is referred to in terms of
octane
number
volatility number
compression number
heptane number
The temperature rise of a gas that is compressed is called
compression ratio
octane number
volatility rating
heat
of compression
The speed with which the flame travels through the burning air-fuel
mixture in the combustion chamber is called the
rate of fuel
burning
rate of flame propagation rate of compression
rate of ignition
has a high-octane rating
A fuel that knocks at low speed
may not knock at high speed
will always knock at high speed
1. The most used internal-combustion-engine fuels are
2.
3.
4.
5.
6.
7.
8.
9.
10.
§109. Detonation versus preignition Thus far, we have been discussing the type of knocking that results from detonation, or sudden explosion, of the last part of the fuel charge in the cylinder.
This type of knocking is usually regular in character and is most
noticeable when the engine is accelerated or is under heavy load,
as when climbing a hill. Under these conditions, the accelerator is
fully open, or nearly so, and the engine is taking in a full air-fuel
charge on every intake stroke. This means that the compression
[171]
§110
Automotive Fuel, Lubricating, and Cooling Systems
pressures are at the maximum; detonation pressures are more apt
to be reached after the mixture is ignited.
There is another type of knocking, which has a different causepreignition. Preignition occurs whenever the air-fuel mixture is
ignited by any means other than the spark at the spark plug. For
example, there might be a build-up of carbon on the piston head.
High spots of the carbon build-up might become hot enough to
glow; these glowing high spots of carbon could ignite the mixture
before the spark occurs. A hot exhaust valve or spark plug might
do the same thing. Even loose particles of carbon floating in the
combustion chamber could cause preignition. The knocking that
results from preignition is irregular; it is often called wild knocking
since it can occur almost any time after the intake valve opens to
start admitting the air-fuel charge.
§110. Chemical control of knocking In the research work on the
problem of finding higher-octane gasolines for the higher-compression engines, many chemical compounds were tested. When added
to the gasoline, some of these compounds had an inhibiting effect
on the fuel that prevented the last part from detonating. One theory
regarding this effect is that the compound retards the rate of flame
propagation through the compressed mixture; this prevents the
rapid pressure rise and "squeezing" of the last part of the compressed charge that would cause it to explode. One of the compounds that was most successful in preventing knocking was tetraethyllead, commonly called ethyl or tel. A small amount added to
gasoline raises the octane, or antiknock, rating of the gasoline.
Within limits, the more added, the higher the octane rating.
§111. Factors
In any particular engine a great
many mechanical factors will affect the tendency to knock. Many
tests have been made to establish the relationship between temperature, humidity, ignition spark advance, engine deposits, and so
forth, and knock tendency. Test results are usually given in terms
of octane-number increase necessary to eliminate knocking. For
example, it is known that a hot engine will knock more easily than a
cold engine. To get exact data on this, an engine is operated cold on
the lowest-octane fuel it can use without knocking. Then it is operated hot on the lowest-octane fuel it can use without knocking. The
difference in octane numbers is an indication of the increased
[172]
affecting knocking
Automotive-engine Fuels
§112
octane requirements as the engine warms up. For example, one
test showed that increasing the temperature of the cooling water
in an engine from 100 to 190°F increased the octane requirements
by 22 numbers (from 50 to 72, for instance). Other tests have
shown the following.
1. A 20° rise in air temperature increases octane requirements
by about three numbers.
2. An increase in humidity from 40 to 50 percent at 85°F reduces
octane requirements by one number. This is laboratory proof
of the common belief that the engine does run better and
more quietly in damp weather.
3. Engine deposits increase octane requirements since they increase the compression ratio (part of the compression space
is taken up by deposits). One series of tests showed that after
about 10,000 miles of operation, engine deposits increased
octane requirements by nine numbers.
4. Advancing the spark or leaning the mixture increases the
octane requirements.
All these factors point up the need for good maintenance of the
modern high-compression engine. Accumulation of scale in the
cooling system, reducing cooling eficn~y;
deposits in the combustion chambers; clogged fuel lines or nozzles in the carburetor,
which lean out the mixture; improper ignition timing-all these
increase the tendency to knock and require an increase of octane
number to prevent knocking.
§112. Chemical versus mechanical octane Octane number can be
increased by adding a chemical such as tel (tetraethyllead). Octane
requirements of the engine can be changed by changes in engine
design as well as by changes in operating conditions. The previous
section discussed several operating conditions that increased or
lowered octane requirements. We have also mentioned the fact
that increasing compression ratio increases octane needs. Mechanical octane (or octane need) of an engine can also be altered by
changes in piston and combustion-chamber shape. Figure 7-6
shows a series of combustion-chamber shapes which were tested
during design work on the Buick V-8 engine. All these were run
under identical conditions of speed, power output, compression
l1731
Automotive Fuel, Lubricating, and Cooling Systems
§1l3
ratio, and so forth. The only variation was in the octane number of
the . fuels used. Fuels were selected for each design as required to
avoid knock. It was found that design A required 96-octane fuel
to run without knocking while design J required only 88-octane
fuel. Thus, there is a difference of 8 mechanical octanes between
design A and design ]. Several reasons for the lower mechanical
octane of design J have been stated. For one thing, the flame-travel
FIG. 7-6. Octane "tree" showing relationship between combustion-chamber
design and octane requirements. Two views of the combustion chamber are
shown for each design (end and side) except for designs F and G . (B'uick Motor
Division of General Motors Corporation)
distance is short so that no distant "pocket" of charge remains to
detonate after most of the fuel has burned. Also, turbulence of the
mixture is high so that no static "pockets" of charge result as the
compression stroke is completed.
§113. Octane requirements Octane requirements of an engine are
determined basically by the engine deSign. However, these requil'ements will change with weather and driving conditions as well as
with the ~nechail
condition of the engine. We have noted in
~1
hO\f changing tempel'ature and humidity change the octane
J174]
'.
\
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Automotive-engine Fuels
§114
needs of the engine. It is also true that engine deposits, reduced
cooling-system efficiency, and carburetor or ignition troubles will
change octane requirements.
In addition to all these, the manner in which the driver operates
the car has a marked effect on octane needs. If the driver is moderate and does not demand quick getaway and high speed, he will
seldom open the throttle wide and his engine will therefore be
much less apt to knock (and thus have lower-octane requirements).
On the other hand, this type of operation tends to hasten engine
deposits; this, of course, means an ultimate increase in octane needs.
The driver who demands full engine power for rapid acceleration
and high-speed operation will need a higher-octane fuel, even with
a new engine.
It is interesting to note that automatic transmissions make a difference in octane needs. With an automatic transmission, the engine
is usually operated at part to full throttle at a fairly high engine
rpm (revolutions per minute). There is very little low-engine-speed,
full-throttle operation such as you find with manual transmissions.
The difference here is, of course, in the manner of coupling. The
manual transmission uses a mechanical clutch that connects the
engine and rear wheels rigidly. But the automatic transmission uses
a fluid coupling or torque converter which allows slippage; on acceleration the engine may turn at high speed while the car is moving
at low speed. Thus, with an automatic transmission, you don't need
to worry about knocking during low-engine-speed, wide-openthrottle operation, because you don't have this type of operation.
Consequently, a fuel such as is indicated by curve A in Fig. 7-5
would be more suitable than fuel B. Fuel A will tend to knock at
low engine speed but not at high engine speed (with spark advance
indicated by curve C in Fig. 7-5). Fuel B will not knock at low
engine speeds but tends to knock at high engine speeds. Section
108 discusses variations in octane of different fuels.
§114. Harmful chemicals and gum in gasoline In addition to haVing
the proper volatility and antiknock properties, gasoline must have
minimum amounts of harmful chemicals and gum-forming substances. For instance, sulfur compounds are often found in gasoline
and, when present in excessive quantities, will cause damage to
engine parts. As the gasoline burns in the engine, the sulfur present
[175]
Automotive Fuel, Lubricating, and Cooling Systems
§115
tends to form sulfur acids. Sulfur acids attack metal parts and
bearings and corrode them. Gum-forming substances may be dissolved in gasoline; as the gasoline evaporates, the gum solidifies in
gasoline passages in the carburetor and intake manifold and on
valves, pistons, and piston rings. Such gum formation can cause
serious difficulty since it hinders the action of the fuel system and
moving engine parts. Insufficient gasoline will be delivered, intake
valves may hang open, and piston rings may stick. Gasoline manufacturers maintain rigid controls in their refineries so as to hold
sulfur compounds and gum-forming substances to a minimum in
their gasolines.
§115. Chemistry of combustion We have already discussed the
combustion process in the engine (§27) and have noted that gasoline is a hydrocarbon (composed of hydrogen-carbon compounds).
The hydrogen and carbon atoms unite with oxygen atoms during
combustion to form water (H20) and carbon dioxide (C02) when
enough oxygen is present. However, in the gasoline engine sufficient amounts of oxygen may not be available, and the oxygen present may not "get to" the carbon. As a result, the carbon does not
attain complete combustion. Some atoms of carbon are able to
unite with only one atom of oxygen (instead of two). This produces
carbon monoxide (CO). Carbon dioxide is a relatively inert and
harmless gas, but carbon monoxide is dangerously poisonous. It
has no color, is tasteless, and has practically no odor. A ratio of 15
parts of carbon monoxide to 10,000 parts of air is dangerous to
breathe. Higher concentrations may cause quick paralysis and
death. Consequently, an engine should never be operated in a
closed space, such as a garage, without Some means of exhausting
the gas into the outside air. Remember this fact: Enough carbon
monoxide can be produced in 3 minutes by an automobile engine
running in a closed 10- by 10- by 20-foot garage to cause paralysis
and death! Never operate an automobile engine with the garage
doors closed!
§116. Diesel-engine fuels You will recall that the diesel engine
compresses air alone on the compression stroke and then injects
fuel oil at the start of the power stroke (§ §93 to 98). The oil is
ignited b)\ the heat of the compressed air so that combustion and
the power "stroke follow. Diesel fuel oil is a relatively light oil, pro\
[176)
\
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Automotive-engine Fuels
§118
duced by a refining process from crude oil, or petroleum. A good
diesel fuel oil must have certain characteristics, including proper
viscosity, cetane number, and freedom from dirt or harmful chemicals. These are discussed below.
§117. Viscosity "Viscosity" is a term that refers to the tendency of
a liquid to resist flowing. Water has a very low viscosity; it flows
very easily. A light oil is more viscous than water, but it still has a
rather low viscosity since it flows quite easily. But a heavy oil flows
slowly; it has a high viscosity. The fuel oil used in a diesel engine
must have a relatively low viscosity so that it will flow easily
through the pumping and injection system that supplies the fuel
to the engine cylinders. It must also be of relatively low viscosity
so that it will spray, or atomize, easily as it is injected into the
cylinder. If it is too viscous, it will not break up into fine enough
particles; this means that it will not burn rapidly enough, and
engine performance will be poor. On the other hand, it must be of
sufficiently high viscosity to lubricate the moving parts in the fuel
system satisfactorily and to help seal the moving parts and prevent
leakage.
§118. Cetane number The cetane number of diesel fuel might be
compared, in a way, to the octane number of gasoline. "Cetane
number" refers to the ignition quality, or ease of ignition, of the
fuel. The lower the cetane number, the higher the temperature required to ignite the fuel. Or, to say it the other way around, the
higher the cetane number, the lower the auto-ignition point (or
temperature required to ignite the fuel). And the higher the cetane
number of a diesel fuel, the less the tendency for the fuel to knock
in the engine. To unders~a
how cetane number and knocking
are related, let us see what causes knocking to occur in a diesel
engine.
You will recall that, at the end of the compression stroke, the
fuel system injects a spray of oil into the compressed air. The oil
is not delivered all at once; it takes an appreciable time for the
delivery. The oil spray starts, continues for a fraction of a second,
and then stops. If the oil does not start to burn almost instantaneously, oil will continue to accumulate. Then, when the oil does
ignite, there will be a considerable amount of oil present which will
ignite and burn almost at the same instant. This will cause a sudden
[177]
Automotive Fuel, Lubricating, and Cooling Systems
§119
pressure rise and knock. At the same time, ignition will not be
complete and smoke will appear in the exhaust gas.
If the cetane number of the fuel is high (ignition temperature
low), the sprayed oil will ignite as soon as injection begins. In this
case, there will be no accumulation of unburned fuel to ignite.
Ignition continues evenly as the spray continues, and an even
combustion-pressure rise results. But if the cetane number of the
fuel is to low, there will be an ignition delay; it takes longer for
the low-cetane fuel to ignite. This then results in the sudden ignition of accumulated fuel and a consequent combustion knock. Since
the fuel may not have sufficient time to burn after it has started,
not all of it may be burned; some will exit from the engine as
smoke.
NOTE: A fuel of excessively high viscosity will also smoke. A
heavy, or viscous, fuel will not atomize properly. The oil particles
will be too large to burn completely, and full combustion will not
take place.
§119. Cetane-number requirements The cetane number of diesel
fuel must be high enough to prevent knock, as noted above. With
low water-jacket temperatures, low atmospheric temperature, low
compression pressures, and light-load operation a higher-cetane
fuel is required. All these conditions tend to reduce compression
temperature. The fuel must, therefore, have a sufficiently high
cetane number (or sufficiently low ignition point) to ignite satisfactOrily at these low temperatures. High-speed diesel engines require high-cetane fuels. At high speed, there is less time for the fuel
to ignite; it must ignite promptly without ignition delay to prevent
knocking and smoking. For starting, the lower the atmospheric
temperature, the higher the cetane requirements.
§120. Fuel-oil purity The oil must have as little sulfur as possible
since sulfur tends to form sulfur acids; these acids will corrode
engine and fuel-system parts. Furthermore, it must be clean. Even
small amounts of dirt or foreign matter are apt to cause trouble in
the fuel system. The fuel system has passages and nozzles of very
small size; small particles can clog them and prevent normal fuelsystem and engine operation. Also, dirt particles can scratch injector parts" and cause serious damage. Thus, suppliers of diesel
[178]
\ \
\
Automotive-engine Fuels
§122
fuel oil are very careful to hold sulfur to a minimum and to use
great care in handling the oil to prevent its being contaminated.
§121. Liquefied petroleum gas Liquefied petroleum gas, or LPG, is
used in more or less standard gasoline-type engines equipped with
special fuel systems (see §99). LPG is made up of certain light
types of hydrocarbon molecules. LPG molecules are related to gasoline molecules: both are made up of hydrogen and carbon atoms.
But LPG molecules are smaller than gasoline molecules so that LPG
is actually a vapor at ordinary temperatures. LPG is found in the
earth along with natural gases and petroleum. It is normally liquid
at the high pressures in the petroleum or gas reservoirs in the earth.
When the pressure is relieved, it turns to gas. In the recovery and
refining process, the LPG is separated from other gas or petroleum
products and pressurized to hold it in liquid form. It is stored and
transported in liquid form in pressurized tanks for convenience.
§122. Types of LPG There are actually two types of LPG that have
been used for automotive-engine fuel, propane and butane. There
are other LPGs, including isobutane, propylene, ethane, ethylene,
and methane. But for automotive purposes either propane or butane
or a mixture of the two is used.
Butane boils, or turns to vapor, at 32°F (at atmospheric pressure). Thus, it cannot be used in an LPG-type fuel system when
temperatures are below 32°F. The reason for this is that at lower
temperatures, it will not vaporize on its way to the carburetor. Nor
will it have enough vapor pressure in the fuel tank to force it out
and through the fuel lines to the carburetor.
On the other hand, propane will boil at -44°F (at atmospheric
pressure). This means that, at temperatures above -44°F, it will
vaporize. It will produce enough vapor pressure in the fuel tank to
force it through the fuel lines and regulator to the carburetor and
will enter the carburetor in vapor form, as required for normal
LPG fuel-system operation.
Thus, in most parts of the country (and of course in the North)
propane alone must be used for automotive fuel. In some places,
butane may be mixed with propane. But in any event, the fuel
must have a sufficiently low bOiling point to vaporize at the air
temperatures in which the vehicle operates.
[179]
Automotive Fuel, Lubricating, and Cooling Systems
§123
§ 123. LPG economy Many large-scale tests of LPG as an engine
fuel have been made. For instance, one large transit company operated a fleet of 500 LPG-operated busses. Trucking companies have
likewise made many tests. Operating figures of gasoline, diesel, and
LPG show that LPG compares favorably with the other fuels so
far as cost per mile is concerned. Since LPG has a high-octane
rating, it can be used in engines having compression ratios of above
10: 1. This makes for efficient utilization of the fuel.
Another factor of importance is that LPG leaves little or no
engine deposit when it burns in the cylinders. Also, since it enters
the engine as a vapor, it cannot wash down the cylinder walls,
remove lubricant, and increase cylinder-wall, piston, and pistonring wear. Nor does it cause crankcase dilution. All these factors
reduce engine wear, increase engine life, and keep maintenance
costs low. However, allowances must be made for the extra cost
of LPG handling equipment. The LPG must be stored in relatively
heavy pressurized tanks, and special equipment must be used to
fill the fuel tanks on the vehicles.
In assessing the possibilities of LPG, many engineers are predicting that LPG will come into wide use for fleet operation of
busses and trucks. It will not be practical in the near future for
passenger cars since it is not available everywhere, as gasoline is.
Few people would want to invest in the special equipment needed
to convert their car to LPG if they were not sure they could buy
LPG anywhere they might like to drive.
CHECK YOUR PROGRESS
Progress Quiz 6
Once again you have a chance to stop and check your progress in
learning about automotive fuel systems. The questions that follow cover
essential details discussed in the past few pages. Answering the questions
not only allows you to test your memory but also helps you review the
important points and thereby fix them more firmly in your mind.
Completing the Sentences
The sentences below are incomplete. After each sentence there are
several words or phrases, only one of which will correctly complete
the sentence.\ Write each sentence down in your notebook, selecting the
'br phrase to complete it correctly.
proper wo~
[180]
\\
\
\
Automotive-engine Fuels
1. Knocking may result from either
detonation or viscosity
detonation or preignition
preignition or humidity
2. After a car with a modern high-compression engine has been driven
10,000 miles, chances are that its octane requirements will have
stayed about the same
risen
fallen
3. So-called wild knocking, which may result from hot spots in the combustion chamber, is due to
detonation
high octane
preignition
4. Two methods of satisfying the octane requirements of an engine are
by
chemical and mechanical means
full-load, full-throttle
operation
increasing compression ratio and power
5. Factors that are of importance in lowering the mechanical octane of
an engine include compression ratio, flame-travel distance in the comchemical octane
fuel viscosity
bustion chamber, and
mixed turbulence
6. When a diesel fuel oil will not break up into fine enough particles
during spraying, so that it does not burn rapidly enough,
its
viscosity is too high
its viscosity is too low
its cetane number is too low
7. The ignition guality, or ease of ignition, of diesel fuel oil is referred
to in terms of its
octane number
heptane number
cetane number
8. A diesel fuel oil that is relatively slow to ignite when it is sprayed
into the compressed air in the combustion chamber has a
relatively high cetane number
relatively low cetane number
relatively high octane number
9. The two LPGs that are most widely used for automotive-engine fuel
are
propane and heptane
propane and cetane
propane and octane
propane and butane
10. The LPG that can be used effectively for engine fuel in cold climates
is
butane
heptane
propane
CHAPTER CHECKUP
NOTE: Since the following is a chapter review test, you should review
the chapter before taking the test.
You have been making excellent progress in your studies of automotive
fuel systems and fuels. The chapters that follow cover servicing procedures on the various types of fuel pumps and carburetors described
in the earlier chapters. Thus, these earlier chapters form the foundation
on which you can build your service-procedure knowledge. In the diagnosis of troubles and in service and repair work it always helps to know
the theory behind the operation of the unit. The chapters you have al[181]
Automotive Fuel, Lubricating, and Cooling Systems
ready covered ill the book give you this theory. Check your memory of
the details covered in Chap. 7 by taking the checkup test that follows.
Completing the Sentences
The sentences below are incomplete. After each sentence there are
several words or phrases, only one of which will correctly complete the
sentence. Write each sentence down in your notebook, selecting the
proper word or phrase to complete it correctly.
1. Important characteristics of gasoline are its
cosity
rating
octane and cetane ratings
volatility and visvolatility and octane
2. Gasoline is blended from a number of different hydrocarbons, each
with its own
cetane
volatility
heptane
LPG
3. Gasoline should have a low volatility for good economy and to combat vapor lock; for easy starting and acceleration it should have a
high volatility
octane
low
viscosity
high
cetane
high
4. The amount that the air-fuel mixture is "squeezed" during the comstroke
heat
pression stroke is determined by the engine
of compression
shape
compression ratio
combustion-chamber
5. Susceptibility of an engine to knocking is increased by combustionchamber deposits as well as by
higher engine temperatures
lower temperatures
higher humidity
6. Other conditions being equal, opening the throttle wide
duces tendency to knock
raises the compression ratio
re-
increases tendency to knock
octane and
cetane and viscosity
7. Characteristics of importance in diesel fuel oil are
heptane
octane and cetane
8. The lower the temperature needed to ignite diesel fuel oil, the
lower the cetane number
higher the cetane number
higher the octane number
9. Diesel fuel oil will smoke from incomplete combustion if the cetane
number is too low or the
octane number is too high
visviscosity is too high
cosity is too low
10. Among the important characteristics of LPG is the fact that it is a
vapor at normal temperatures and
is a liquid at high temperatures
has a high-octane rating
is fast burning in com-
bustion chamber
Definitions and Characteristics
In the following, you are asked to write down certain definitions and
characteristics that are related to various fuels discussed in the chapter.
[182]
\
Automotive-engine Fuels
If you have any difficulty in answering the questions, reread the pages
that will give you the answer; then write down your definition. Don't
copy from the book; use your own words. This is a good way to fix the
explanation firmly in your mind. Write in your notebook.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Define volatility.
What is vapor lock?
What is compression ratio?
What is the effect on octane requirements as compression ratio is
increased?
Describe one method of measuring antiknock value of gasoline.
What causes preignition?
What are some of the factors affecting knocking?
What is meant by mechanical octane of an engine?
Define viscosity.
What is cetane number of diesel fuel oil, and how is it related to
temperature?
Which is the more widely used LPG for automotive vehicles, propane
or butane?
What are some characteristics of LPG?
SUGGESTIONS FOR FURTHER STUDY
To learn more about automotive engines, refer to Automotive Engines,
another book in the McGraw-Hill Automotive Mechanics Series. If you
are interested in learning more about gasoline and other fuels, you may
find books in your local public or school automotive library that can
supply you with additional information. Also, manufacturers of special
equipment and vehicles using LPG and diesel fuel oil issue special service manuals that supply further data on the equipment. You may be able
to examine these manuals in a local truck or bus shop where this equipment is serviced. Write down in your notebook any important facts you
learn.
[183]
8: Diagnosing fuel-system
troubles
THE PURPOSE of this chapter is to supply detailed information on
the various kinds of trouble that the fuel system has and to explain
the procedures used to determine the causes of these. troubles.
Following chapters then describe the procedures required to make
corrections.
§ 124. How to study this chapter There are different ways to study
this chapter. You could go through it page by page, just as you have
studied the previous chapters. But perhaps a better way would be to
take one complaint at a time (as listed in the trouble-shooting
chart), read through the possible causes and corrections, or checks,
and then study the section later in the chapter that discusses the
complaint. For example, you could take 1. Excessive fuel consumption, and after reading the causes and checks or corrections
listed in the second and third columns in the chart, you could turn
to §137, which describes these causes and checks or corrections in
more detail.
Since a knowledge of trouble causes and corrections is very helpful, you will probably be referring to the trouble-shooting chart
many times. One way to help yourself remember the complaints,
causes, and corrections is to write each complaint, with all or some
of the causes and corrections, on a separate 3- by 5-inch card. Then
you can carry the cards around with you. Whenever you have a
chance, you can pull the cards out and study them. You could
stick one in the mirror before you when you shave in the morning,
or study one or two of them while riding the bus to work or when
you are eating lunch, and so on. Soon, you will know the troubles
and their causes and corrections "from A to Z."
§125.
Need ~or
logical procedure Another book in the McGrawHill Automotive Mechanics Series (Automotive Engines) describes
[184]
Diagnosing Fuel-system Troubles
§127
in detail how to diagnose engine troubles and to trace them down
to the faulty part or unit. If the trouble is traced down to the fuel
system, some further checking may be desirable in order to pinpoint the trouble exactly. The following pages outline in detail the
fuel-system checks to make as well as the corrections needed to
eliminate the troubles.
It is always desirable to follow a logical procedure in diagnosing
any fuel-system trouble since there are many conditions that could
be the cause of a trouble. The basic complaints that might arise
from faulty operation of the fuel system are described below, and
under each complaint the possible causes are listed. When a specific complaint arises, then the causes under that complaint should
be checked. Such a procedure saves the time and motion which
might otherwise be wasted in checking things that normally would
not cause the complaint.
§126. Testing
A variety of instruments are available
for testing the fuel system and engine performance. These include
fuel-mileage testers, which measure fuel consumption per mile of
car travel; exhaust-gas analyzers, which check the air-fuel mixture;
low-pressure gauges for measuring fuel-pump pressure; fuel-pump
capacity testers; vacuum gauges for measuring fuel-pump vacuum
and intake-manifold vacuum; rpm (revolutions per minute) indicators, or tachometers, for checking engine speed; and dynamometers for measuring engine power output. In addition, special
tools are required for servicing the carburetor and the fuel pump.
instruments
§127. Fuel-mileage testers A complaint which is sometimes difficult
to analyze is low fuel mileage. Many conditions can cause excessive
fuel consumption; thus it is sometimes necessary to make an accurate measurement of the fuel consumed if the cause of the trouble
appears elusive. Fuel-mileage testers vary from a fuel meter that
measures fuel consumption accurately (Fig. 8-1) to a simple device
that consists of a container that holds a definite amount of gasoline
and a tube to connect the container to the carburetor. A simple
version of the latter may be made from a can with a supporting
handle for mounting under the hood and a fitting for the tube. The
can must be above the carburetor so that the fuel will run from
the can to the carburetor. The test is performed by disconnecting
the line to the fuel tank and then operating the car until the gaso[185]
Automotive Fuel, Lubricating, and Cooling Systems
§128
line in the carburetor is used up. The container may then be
mounted and connected to the carburetor, a definite amount of
gasoline being placed within the container after mounting. The
car should be operated until this gasoline is used up, and an accurate mileage record should be kept.
FIG. 8-1. Fuel-mileage tester as it looks from outside and inside of car when
mounted in place ready for test. (Kent-Moore Organization, Inc.)
§128. Exhaust-gas analyzers Exhaust-gas analyzers (Fig. 8-2) are
valuable in checking carburetor calibrations, adjustments, and performance. They test the exhaust gas from the engine by various
methods, and this test determines whether or not the ratio of fuel
and air entering the cylinders is correct, provided other components
are functioning normally. As was mentioned in §1l5, the gasoline,
composed principally of hydrogen and carbon compounds, unites
with the oxygen in the air during combustion in the engine to
form water (hydrogen and oxygen, H20 ), carbon dioxide (carbon
and oxygen, C02), carbon monoxide (carbon and oxygen, CO) and
negligible amounts of other products. With an ideal mixture of
fuel and air entering the combustion chamber, and with perfect
combustion conditions, all the oxygen in the air would unite with
all the hydrogen and carbon components in the fuel to form water
and carbon dioxide. This does not normally happen, however, and
some unburned combustibles, as well as carbon monoxide, can
invariably be found in the exhaust gas. As the ratio between the
fuel and air entering the combustion chamber changes, the proportions of carbon dioxide, carbon monoxide, and unburned combustibles in the exhaust gas change. Thus, analysis of the exhaust gas
gives a very, accurate determination of the proportions of fuel and
air entr~
'the combustion chamber. Three types of exhaust-gas
[186]
!\
\
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Diagnosing Fuel-system Troubles
§129
8-2. Instrument connections for making an exhaust-gas analysis (or com bustion efficiency test). Note that the pickup gun is installed in tail pipe and is
connected by a hose to the analyzer. A small pump, or booster, draws exhaust
gas through the hose to the analyzer. (Sun Electric Corporation)
FIG.
analyzer are in use. These are the thermal-conductivity, hot-wirecatalysis, and relative-density types. A detailed analysis of their
operation is contained in the Appendix.
§129. Low pressure gauges for measuring fuel-pump pressure The
pressure at which the fuel pump delivers fuel to the carburetor
must be within definite limits. If it is too low, insufficient fuel will
be delivered and faulty engine performance will result, since the
air-fuel mixture will tend to lean out excessively at high speed or
on acceleration. If the pressure is too high, flooding may result, and
the mixture will be too rich, causing the engine to be logy. An
overrich mixture will also cause engine trouble from carbon deposits in the combustion chambers and on valves and rings. Also,
crankcase dilution and rapid wear of engine parts will probably result. Fuel-pump pressure may be tested with a low-pressure gauge
connected to test either static pressure or flow pressure. In the
static-pressure test the gauge is connected to the outlet of the fuel
pump, and the engine is mn at approximately thirty mph (miles
per hour) on the fuel in the carburetor while the static fueJ pressure is checked. In the flow-pressure test the gauge is connected
into the fuel line between the pump and the carburetor with a T
fitting (Fig. 8-3), and the engine is idled with the pump delivering
[187J
Automotive Fuel, Lubricating, and Cooling Systems
§130
FIG. 8-3. Using a low-pressure gauge to check fuel-pump flow pressure. 1, fuei
gauge; 2, line to fuel pump. (Plymouth Division of Chrysler Corporation)
fuel to the carburetor in the normal manner. Specifications vary
considerably from one type of pump to another, but in general they
will specify hom 17fl to 5 pounds static pressure and about 25 percent less flow pressure.
§130. Fuel-pump capacity testers The fuel-pump capacity tester is
a device that measures the amount of fuel the pump can deliver
in a given time. The device is connected with a T fitting into the
line at the carburetor and bleeds off a portion of the fuel passing
in the line. The amount that can be bled off with the engine running is determined by the capacity and operating condition of the
pump.
§131. Fuel-pump vacuum tester The fuel-pump vacuum tester is a
vacuum gauge which is connected to the inlet side of the fuel
pump so that the amount of vacuum the pump can produce is
measured. During this test, fuel lines are disconnected from both
inlet and outl'et sides of the fuel pump and the engine is run tem\
[188]
),
\.
Diagnosing Fuel-system Troubles
§133
porarily on the fuel in the carburetor float bowl. The vacuum pump
of the combination pump can also be tested with the vacuum
gauge.
§132. Vacuum
The
intake-manifold vacuum varies considerably under different operatgauges for measuring intake-manifold vacuum
FIG. 8-4. Instrument connections for making manifold-vacuum test. The vacuum
gauge shown here is built into a panel as part of a test stand. (Sun Electric
Corporation)
ing conditions, and it also varies with faulty engine performance.
The various troubles that might occur in the engine, ignition, or fuel
systems are reflected by characteristic manifold-vacuum changes.
Thus, a· manifold-vacuum gauge that shows these changes will provide a good indication of the type of trouble (see Fig. 8-4). Faulty
carburetor action, for example, is indicated by a slow oscillation of
the vacuum-gauge needle or by an irregular drop from a normal
reading. The procedure of testing the engine with a vacuum gauge
is detailed in another book in the McGraw-Hill Automotive Mechanics Series (Automotive Engines). The vacuum gauge can also
be used in making the carburetor idle-mixture adjustment (§ 169) .
§133. Tachometers Tachometers, or rpm indicators, are used to
measure the speed at which the engine is running. Many engine
manufacturers specify that carburetor adjustments be made so as
to give an idle speed of so many engine revolutions per minute.
This is particularly important on cars equipped with automatic
[189]
Automotive Fuel, Lubricating, and Cooling Systems
§134
transmissions: incorrect idle-speed settings may prevent normal action of the transmission. The tachometer used in the service shop
has a pair of leads to connect into the ignition system (Fig. 8-5).
Then, when the engine is running, the tachometer, in effect, counts
the number of electrical impulses per minute in the ignition primary and translates this information into revolutions per minute.
FIG. 8-5. Electric connections to check engine revolutions per minute with
tachometer. Selector knob must be turned to four-, six-, or eight-lobe position,
according to number of engine cylinders (or number of lobes on distributor
cam). (Sun Electric Corporation)
An adjustment is included on the tachometer so that it can be set
for four-, six-, or eight-cylinder engines.
§134.
The chassis dynamometer tests the actual power output of the engine. Since carburetor adjustments and
operation, as well as many other factors, affect power output, a
thorough analysis of engine performance would require a dynamometer test. This type of apparatus is shown in Fig. 8-6. The
dynamometer is driven through the car rear wheels with the car
in gear and the engine running.
Chassis dynamometers
§135. Trouble tracing in fuel system The tracing of trouble in the
fuel system is usually fairly straightforward; fuel-system troubles
fall into several definite classifications that require definite corrections. However, there is sometimes a question as to whether
the cause of complaint lies in the fuel system or in some other engine component. Thus, the real problem is often to isolate the trouble
in the improperly operating component. The trouble sometimes
[190]
\
\
Diagnosing Fuel-system Troubles
§135
may be made more puzzling because it could result in not one condition but several. For example, suppose the full-power, vacuumoperated valve in the carburetor holds open. This would produce
an excessively rich mixture for all running conditions except fullpower, open-throttle operation. This, in tum, would not only cause
excessive fuel consumption, but might ultimately foul the spark
FIG. 8-6. Automobile in place on chassis dynamometer. Rear wheels drive the
dynamometer rollers, and instruments on test panel indicate car speed, engine
power output, engine speed, engine intake-manifold vacuum, air-fuel ratio, etc.
(Clayton Manufacturing Company)
plugs to cause poor ignition and missing; also, the carbon deposits
might cause defective piston ring and valve action.
The chart that follows lists the various troubles that might be
blamed on the fuel system, together with their possible causes,
checks to be made, and corrections needed. This chart might be
considered as a further development of the comprehensive troubleshooting chart contained in Automotive Engines (another book
in the McGraw-Hill Automotive Mechanics Series).
[191]
Automotive Fuel, Lubricating, and Cooling Systems
§136
§136. Fuel-system trouble-shooting chart Most fuel-system troubles
can be listed under a few headings: excessive fuel consumption,
poor acceleration, lack of power and high-speed performance, poor
idle, engine will not start except when primed, hard starting, slow
warm-up, stalling, smoky exhaust, and backfiring. The chart that
follows lists possible causes of each of these troubles, and then refers to numbered sections after the chart for fuller explanations of
the way to locate and eliminate the troubles. When trouble has
been traced to some component outside the fuel system, reference
is made to the book in the McGraw-Hill Automotive Mechanic Series that provides necessary servicing information.
NOTE: The troubles and possible causes are not listed in the
chart in the order of frequency of occurrence. That is, item 1 (or
item a under Possible Causes) does not necessarily occur more frequently than item 2 (or item b). Generally, the fuel-system troubles and possible causes are listed first in the chart even though,
in many cases, other automotive components are more apt to have
caused the troubles listed.
FUEL-SYSTEM TROUBLE-SHOOTING CHART
(See §§137 to 147 for detailed explanations of trouble causes and corrections listed below.)
Complaint
1. Excessive fuel
consumption
( §137)
\
rabbit" driver
b. High speed
c. Short-run and
"start and stop"
operation
d. Excessive
fuelpump pressure or
pump leakage
e. Choke not opened
properly
\\
f.
\, \
'192)
Possible Cause
a. Nervous or "jack-
\,
C log g e d air
cleaner
g. High carburetor
float level or float
leaking
Check or Correction
Drive more reasonably
Drive more slowly
Make longer runs
Reduce pressure; repair pump
Open; repair or replace automatic
choke
Clean
Adjust or replace float
Diagnosing Fuel-system Troubles
§136
Complaint
Possible Cause
Check or Correction
1. Excessive fuel
consumption
h. Stuck or dirty float
Free and clean or replace
Replace
(§137)
needle valve
i. Wom carburetor
jets
j. Stuck metering rod
or full-power piston
k. Idle too rich or too
fast
I. Stuck accelerator
pump check valve
m. Carburetor leaks
n. Faulty ignition
o. Loss of engine
compression
p. Defective valve
action
q. Excessive rolling
resistance from
low tires, dragging
brakes, wheel misalignment, etc.
r. Clutch slipping
2. Engine
lacks
power, acceleration, or high-speed
performance
(§l38 )
" See
t See
t See
§ See
a. Accelerator pump
Free
Readjust
Free
Replace damaged
parts; tighten loose
couplings, jets, etc.
Check coil, condenser,
plugs,
conta,ct
points, wiring"
Check compression;
repair enginet
Check compression;
repair enginet
Correct cause of rolling resistancet
Adjust
or
repair
clutch§
Adjust; free; repair
malfunctioning
b. Power step-up on
metering rod not
clearing jet
c. Power piston or
valve stuck
d. Low float level
e. Dirt in filters or in
line or clogged
fuel-tank-cap vent
Free or adjust
Free
Adjust
Clean
Automotive Electrical Equipment.
Automotive Engines.
Automotive Chassis and Body.
Automotive Transmissions and Power Trains.
[193]
f
f
I
Automotive Fuel, Lubricating, and Cooling Systems
§136
Complaint
2. Engine
lacks
power, acceleration, or high-speed
performance
(§138)
possible Cause
Choke stuck or not
operating
g. Air leaks around
carburetor
h. Antipercolator
valve stuck
i. Manifold
heatcontrol
valve
stuck
j. Throttle valve not
fully opening
k. Rich mixture due
to worn jets, high
float level, stuck
choke, clogged air
cleaner
1. Vapor lock
f.
m. Fuel pump defective
n. Clogged exhaust
o. Ignition defective
p. Loss of compression
q. Excessive carbon
Check or Correction
Adjust or repair
Replace gaskets;
tighten nuts or bolts
Free; adjust
Free
Adjust linkage
Adjust; repair; clean;
replace worn jets
Use different fuel or
shield fuel line
Service or replace
Clean
Check timing, coil,
plugs, distributor,
condenser, wiring"
Check engine compression; repair enginet
Clean outt
in engine
r. Defective
\
\
\
valve
action
s. Heavy engine oil
t. Cooling system not
operating properly
\
u. Engine overheats
\\
v. Excessive
rolling
<> See Automotive Electrical Equipment.
t See Automo,tive Engines.
t See Automotive Chas8is and Body.
§ See Aut0m.0tive Trammissions and Power Trains.
[194]
Check compression;
repair enginet
Use lighter oil
Check
thermostat;
flush system
(see §§249 to 252)
Check cooling system
(see §251)
Correct the defect
Diagnosing Fuel-system Troubles
Complaint
2. Engine
lacks
power, acceleration, or high-speed
performance
(§138)
3. Poor idle (§139)
4. Engine will not
start except when
primed (§140)
5. Hardstartingwith
engine
warm
(§141)
Possible Cause
resistance from
low tires, dragging
brakes, wheel misalignment, etc.
w. Clutch slippage or
excessive friction
in power train
a. Idle mixture or
speed not adjusted
b. 0 the rca use s
listed under Engine lacks power,
etc. (item 2,
above)
a. Line clogged
b. Fuel pump defective
c. Carburetor jets or
lines clogged
d. Filter clogged
e. Air leaks into intake manifold or
carburetor
a. C h 0 k eva 1 v e
closed
b. Manifold heatcontrol
stuck
closed
c. Throttle-cracker
linkage out of adjustment
d. Vapor lock
e. Eng i n e
6. Slow
engine
warm-up (§142)
parts
binding
a. Choke valve open
b. Manifold heatcontrol
valve
stuck open
"Cooling-system
thermostat stuck
open
§136
Check or Correction
causing rolling resistancet
Adjust or repair§
Readjust
Clear
Repair or replace
Clean
Clean
Replace gaskets;
tighten nuts or
bolts
Open; adjust or repair
Open; free valve
Adjust
Use correct fuel or
shield fuel line
Repair enginet
Adjust or repair
Close; free valve
Free; replace
necessary
if
[1951
Automotive Fuel, Lubricating, and Cooling Systems
§136
Complaint
7. Smoky, black exhaust (§143)
8. Engine
stalls
when cold or as
it warms up
(§144)
9. Engine
stalls
after idling or
slow-speed driving (§144)
10. Engine
stalls
after high-speed
driving (§144)
11. Engine backfires
(§145 )
12. Engine runs but
misses (§146)
\
° See Aut~ive
t See Aut~oive
[196]
Possihle Cause
a. Very rich mixture
Check or Correction
( see §137 on excessiVE
fuel consumption)
NOTE: A blue exhaust means excessive oil consumption (see §227)
a. Choke valve stuck
Free; adjust
or choke inoperative
h. Manifold heatOpen; free
control
valve
stuck closed
c. Engine overheats
(see §251)
a. Defective fuel
pump
h. Engine overheats
Repair or replace
a. Vapor lock
Use different fuel or
shield fuel line
Adjust or repair
h. Antipercolator
malfunctioning
c. Engine overheats
a. Excessively rich
or lean mixture
h. Overheating of
engine
c. Engine conditions
such as excessive
carbon, hot valves,
overheating
d. Ignition timing incorrect
e. Spark plugs of
wrong heat range
a. Fuel pump erratic
in operation
h. Carburetor jets or
lines clogged or
worn
Electrical Equipment.
Engines.
'\
) \
(see §251)
(see §251)
Repair or readjust fuel
pump or carburetor
(see §251)
Repair enginet
RetimeO
Install correct plugsO
Repair or replace
Clean or replace
Diagnosing Fuel-system Troubles
Complaint
12. Engine runs but
misses (§146)
Possible Cause
c. Fuel level not correct in float bowl
d. Ignition system
defects such as incorrect timing or
defective
plugs,
coil, points, cap,
condenser, wiring
e. Clogged exhaust
f.
Engine overheating
g. Engine conditions
such as valves
sticking, loss of
compression, defective rings, etc.
§137
Check or Correction
Adjust float; clean
needle valve
Check ignition system'"
Check tail pipe, muffler; eliminate clogging
(see §251)
Check enginet
§137. Excessive fuel consumption The first step in analyzing a complaint of excessive fuel consumption is to make sure that the car is
really having this trouble. Usually, this means taking the word of
the car owner that his car is using too much fuel. A fuel-mileage
tester (§127) can be used to determine accurately how much fuel
the car is using. After it has been determined that the car is using
too much fuel, then the cause of trouble must be found. It could
be in the fuel system, ignition system, engine, or elsewhere in the
car.
The compression tester and the intake-manifold vacuum gauge,
described in another book in the McGraw-Hill Automotive Mechanics Series (Automotive Engines), will determine the location
of trouble and whether it is in the fuel system, ignition system,
engine, or elsewhere. 1
If the trouble appears to lie in the fuel system, the following
points should be considered.
l. A nervous driver or one who pumps the accelerator pedal
1 A rough test of mixture richness that does not require any testing instruments is
to install a set of new or cleaned spark plugs of the correct heat range for the engine. Then take the car out on the highway for 15 or 20 minutes. Stop the car, remove and examine the plugs. If they are coated with a black carbon deposit, the
indication is that the mixture is too rich. See points 4 to 7, §137.
[197]
§137
Automotive Fuel, Lubricating, and Cooling Systems
when idling and "jack-rabbits" when starting because he insists on
being the first to get away when the stop light changes uses an excessive amount of fuel. Each downward movement of the accelerator pedal causes the accelerator pump to discharge a flow of gasoline into the carburetor air horn. This extra fuel is wasted since it
~ontribues
nothing to the movement of the car.
2. High-speed operation requires more fuel per mile. A car that
will give 20 miles per gallon at 30 mph may give less than 15 miles
per gallon at 60 mph. At 70 or 80 mph the mileage may drop to
well below 10 miles per gallon. Thus, a car operated consistently
at high speed will show poorer fuel economy than a car driven consistently at intermediate speed.
3. Short-run, "stop and start" operation uses up more fuel. In
short-run operation, with the engine allowed to cool off between
runs, the engine is operating mostly cold or on warm-up. This
means that fuel consumption is high. When the car is operated
in heavy city traffic, or under conditions requiring frequent stops
and starts, the engine is idling a considerable part of the time. Also,
the car is accelerated to traffic speed after each stop. All this uses
up a great deal of fuel, and fuel economy will be poor.
4. If the fuel pump has excessive pressure, it will maintain an
excessively high fuel level in the carburetor float bowl. This will
cause a heavier discharge at the fuel nozzle or jet, thereby producing high fuel consumption. Excessive pump pressure is not a common cause of excessive fuel consumption, however, since it could
result only from installation of the wrong pump or diaphragm
spring or from incorrect reinstallation of the pump diaphragm during repair. However, pumps can develop leaks that will permit loss
of gasoline to the outside or into the crankcase; this requires replacement of the diaphragm, tightening of the assembling screws,
or replacement of the pump (§ 158 to 165).
5. If a manually operated choke is left partly closed, the carburetor will deliver too much fuel for a warm engine, and fuel consumption will be high. On manually operated chokes, it is possible
for the choke-valve linkage to get out of adjustment, so that the
valve will not open fully; this will require readjustment to prevent
high fuel consumption (§ 150 ) .
With an:" automatic choke, the choke valve should move from
closed to\ 6pen position during engine warm-up, reaching fullwhen the engine reaches operating temperature. This
open posit~n
[198]
,\
Diagnosing Fuel-system Troubles
§137
action can be observed by removing the air cleaner and noting the
changing position of the choke valve during warm-up. If the automatic choke does not open the choke valve normally, excessive fuel
will be used. The choke must be serviced (§§151 to 153).
6. A clogged air cleaner (on unbalanced carburetor) acts much
like a closed choke valve (see §57) since it chokes off the free flow
of air through it. The cleaner element should be cleaned or replaced and fresh oil added (on type of cleaner using oil). See
§149.
7. In the carburetor itself, the following conditions could cause
delivery of an excessively rich air-fuel mixture (see Chap. 10, "Carburetor Service," for corrections).
a. High float level or leaking float will permit delivery of too
much fuel to the float bowl and consequently through the fuel
nozzle or jet. The float level must be readjusted or a leaky
float replaced.
b. A stuck or dirty float needle valve will not shut off the flow
of fuel from the fuel pump, so that too much will be delivered
through the carburetor fuel nozzle or jet. The needle valve
should be freed and cleaned or replaced.
c. Worn carburetor jets pass too much fuel causing the air-fuel
mixture to be too rich. Worn jets must be replaced.
d. If the full-power circuit operates during part-throttle operation, too much fuel will be delivered through the main fuel
nozzle. This could be due to a stuck metering rod or fullpower piston, which must be freed.
e. An idle that is set too rich or too fast wastes fuel. Resetting of
the idle richness and speed is required.
f. If the accelerator-pump check valve sticks open, it may permit discharge of fuel through the pump system into the carburetor air horn, causing excessive fuel consumption. This requires freeing and servicing of the check valve.
g. Carburetor leaks, either internal or external, cause loss of fuel.
Correction is to replace gaskets or damaged parts and tighten
loose couplings on fuel lines, loose jets or nozzles, and loose
mounting nuts or screws.
8. Faulty ignition can also cause excessive fuel consumption since
the ignition system could cause engine miss and thus failure of the
engine to utilize all the fuel. This type of trouble would also be
[199]
Automotive Fuel, Lubricating, and Cooling Systems
§138
associated with loss of power, acceleration, or high-speed performance (§138). Conditions in the ignition system that might cause
the trouble include a "weak" coil or condenser, incorrect timing,
faulty advance mechanism action, dirty or worn spark plugs or
contact points, and defective wiring.
9. Several conditions in the engine can also produce excessive
fuel consumption. Loss of engine compression from worn or stuck
rings, worn or stuck valves, or a loose or burned cylinder-head gasket causes loss of power. This means that more fuel must be burned
to achieve the same speed or power.
10. Any condition that increases rolling resistance and makes it
harder for the car to move along the road will increase fuel consumption. For example, low tires, dragging brakes, and misalignment of wheels increase fuel consumption. Similarly, losses in the
power train, as, for instance, from a slipping clutch, will increase
fuel consumption.
§138.
\
Engine lacks power, acceleration, or high-speed performance
This type of complaint is usually rather difficult to analyze since it
is, after all, somewhat vague. Almost any component of the engine
or car, from the driver to the tires, could cause the complaint. As
a first step in solving this sort of complaint, some mechanics take
the car out for a road test. The car can be accelerated over a good
road with a stop watch used to determine how long it takes to reach
a given speed. The test should be made on the road first in one
direction and then in the other and the results averaged, so that
such variables as wind and road grade are balanced out. The engine
can also be checked on the chassis dynamometer (§ 134) or be
given a comprehensive tune-up as detailed in Automotive Engines
(another book in the McGraw-Hill Automotive Mechanics Series).
Conditions that might cause the complaint are discussed in following paragraphs, with the fuel-system conditions considered first.
1. Almost any out-of-balance condition in the carburetor could
prevent delivery of proper amounts of fuel for good acceleration
and full power. Possibilities to be considered follow (see Chap. 10,
"Carburetor Service").
a. Incor~t
[200]
functioning of the accelerator pump. On many engines'\the action of the accelerator pump can be checked by
\
/\
I
\
\
Diagnosing Fuel-system Troubles
§138
removing the air cleaner and observing the accelerator-pump
discharge jet when the throttle is opened. If the pump is
functioning correctly, a steady stream of fuel will be discharged from the jet as the throttle is opened. The stream
should continue for some moments after the throttle has
reached full-open position. If the pump does not operate correctly, disassembly and servicing is required. Some pumps can
be adjusted to change the amount of fuel delivered during
acceleration.
h. If the power step-up diameter on the metering rod does not
clear the metering-rod jet with wide-open throttle, insufficient
fuel will be delivered for full-power performance. This requires
readjustment of metering-rod linkage.
c. Similarly, if the full-power piston or valve sticks so that the
valve cannot open for full power, insufficient fuel will be
delivered. The piston or valve must be freed and cleaned.
d. A low float-level adjustment will "starve" the main nozzle or
jet, preventing delivery of normal amounts of fuel and causing
loss of engine power. The float level should be readjusted.
e. Dirt in filters or line will also "starve" the carburetor main
nozzle or jet and the engine since it will tend to restrict fuel
passage. Also, a clogged fuel-tank-cap vent will restrict the
passage of air into the tank as gasoline is withdrawn. This
creates a partial vacuum in the tank that works against the
pump; fuel delivery to the carburetor is cut down. Dirt must
be cleaned out of the cap vent, filters, and line.
f. A stuck or inoperative choke will cause loss of power when the
engine is cold. It may also cause loss of power with the engine
hot if it is stuck in a partly closed position, since this produces
an excessively rich mixture. The choke should be serviced.
g. If air leaks into the intake manifold around the carburetor or
manifold mounting, or past worn throttle-shaft bearings, the
air-fuel mixture may become too lean for good operation.
Gaskets should be replaced and mounting nuts or screws
tightened as necessary. Excessively worn throttle-shaft bearings
require carburetor body replacement.
h. A stuck antipercolator valve may also cause an excessively
lean mixture and requires freeing or adjustment.
i. A stuck manifold heat-control valve, if stuck in the closed
[201]
Automotive Fuel, Lubricating, and Cooling Systems
§138
position, overheats the air-fuel mixture in the intake manifold
with the engine hot, so that the mixture expands excessively.
This "starves" the engine, causing inferior performance. If the
valve sticks open, warm-up will be slowed. The valve should
be freed.
j. If the throttle-valve linkage is out of adjustment, the throttle
may not open fully, preventing delivery of full power. Throttle
linkage should be correctly adjusted (§ 168 ).
k. Most of these conditions produce an excessively lean mixture.
However, conditions that produce an excessively rich mixture
(see §137) also cause poor engine performance.
2. Vapor lock also causes fuel "starvation" in the engine. Vaporization or boiling of the fuel in the fuel pump or fuel line prevents
delivery of normal amounts of fuel to the carburetor and carburetor nozzles and jets. Some mechanics check for this condition by
inserting a glass tube in the fuel line and then watching for bubbles
to pass through the tube with the engine hot and running. Correction is to use a fuel with lower volatility or to shield the fuel line
from engine heat.
3. A defective fuel pump might also "starve" the engine by not
delivering sufficient amounts of fuel to the carburetor. This requires
servicing or replacement of the fuel pump (§§157 to 165).
4. A clogged exhaust due to rust, dirt, or mud in the muffler or
tail pipe or a pinched or damaged muffler or tail pipe could create
sufficient back pressure to prevent normal exhaust from the engine.
This would result in reduced engine performance, particularly on
acceleration or at high speed.
5. Defective ignition can reduce engine performance, just as it
can increase fuel consumption (§137, 8). Conditions in the ignition
system that might cause the trouble include a "weak" coil or condenser, incorrect timing, faulty advance mechanism action, dirty or
worn spark plugs or contact points and defective wiring.
6. A sluggish engine will result from loss of compression, excessive carbon in the engine cylinders, defective valve action, or
heavy engine oil.
7. Failure of the cooling system to operate properly could cause
the engine \~o overheat with a resulting loss of power (§251). Also,
if the cooling-system thermostat fails to close as the engine cools,
[202]
"
\
\
\
\
Diagnosing Fuel-system Troubles
§140
it will prolong engine warm-up the next time the engine is started.
This reduces engine performance during warm-up.
8. Any condition that increases rolling resistance will reduce
acceleration and top speed. These conditions include low tires,
dragging brakes, and misalignment of wheels.
9. Clutch slippage or excessive friction in the power train will
reduce acceleration and top speed.
§139.
Poor idle If the engine idles roughly, too slow, or too fast,
the probability is that the idle mixture and idle speed require adjustment as explained in §l68. In addition, a malfunctioning choke,
a high or low float level, vapor lock, clogged idle circuit, air leaking
into the intake manifold, loss of engine compression, improper valve
action, overheating engine, improperly operating ignition system,
all of which were discussed in the previous section, would cause
poor idle. These latter conditions, however, would also cause poor
engine performance at speeds above idle. Improper idle-mixture or
idle-speed adjustment becomes obvious only with the engine idling.
§140.
Engine will not start except when primed When the engine
turns over at normal cranking speed but will not start, the trouble
is probably in the ignition or fuel system. The ignition system can
be quickly checked by disconnecting the lead from one spark plug
and holding the lead clip about three-sixteenths of an inch from the
engine block while cranking. If a good spark occurs, the ignition
system is probably operating normally, although it could be out of
time (see Automotive Electrical Equipment).
If the ignition system operates normally, the engine should be
primed by removing the air cleaner and squirting a small amount
of fuel from an oil can into the carburetor air cleaner while
cranking.
Caution: Gasoline is highly explosive. Keep back out of the way
when priming the engine; the engine might backfire through the
carburetor.
If the engine starts and runs when primed, failure to run normally means that the carburetor is not delivering fuel to the engine.
This could be due to clogged lines or jets in the carburetor, a
clogged filter, a defective fuel pump, clogged fuel line, or an empty
fuel tank. Pump action may be tested by temporarily loosening the
[203]
§141
Automotive Fuel, Lubricating, and Cooling Systems
fuel line at the carburetor and then cranking briefly to see if the
fuel pump is delivering fuel. (Catch fuel in a container or cloth,
and then put cloth outside to dry.)
If the fuel pump does not deliver fuel, it must be removed for
repair (§ §157 to 165). If the fuel pump does deliver fuel, the carburetor is defective, and it must be serviced (see Chap 10, "Carburetor Service").
§141. Hard starting with engine warm If the engine starts hard
when warm, it could be due to the choke sticking closed, improper
throttle-cracker linkage, vapor lock (§I3S, 2), or engine binding
due to overheating. Choke action can be watched with the air
cleaner removed. If the choke does not open wide with the engine
hot, it should be serviced (§ §151 to 153 ) .
If the engine warms up slowly, the
trouble could be due to an open choke (it should be partly closed
with the engine cold); this can be seen with the air cleaner off.
Also, the manifold heat-control valve or the cooling-system thermostat could be stuck open.
§142. Slow engine warm-up
§143. Smoky, black exhaust
A smoky, black exhaust means that
the air-fuel mixture is very rich. Not only does this greatly increase
fuel consumption, but also it causes rapid formation of carbon in
the engine cylinders, fouling of plugs, and sticking of valves. Section
137, which discusses fuel consumption, describes various causes of
the trouble.
NOTE: A smoky, blue exhaust means excessive oil consumption
( §227).
§144. Engine stalls The engine will stall under various conditions,
and as a first step in determining the cause, the condition under
which it stalls should be noted.
1. If the engine stalls when cold, the choke may not be closed as
it should be with the engine cold. Choke action should be checked
and adjustment made as necessary (§§150 to 153).
2. If the engine stalls as it warms up, the choke could be stuck
closed, causing an overrich mixture; or the manifold heat-control
valve coul~
be stuck closed; or the engine may be overheating.
3. If tfle engine stalls after idling or slow-speed driving, the
chances are that the fuel pump is defective and has a cracked
[204]
Diagnosing Fuel-system Troubles
§147
diaphragm, weak spring, or defective valve. In such case, the pump
cannot deliver enough fuel at low speed to replace that delivered
by the engine. The carburetor float bowl runs dry and the engine
stops. In addition, the engine may overheat during sustained idling
or slow-speed driving since with this type of operation air movement through the radiator may not be great enough to keep the
engine cool.
4. If the engine stalls after a period of high-speed or full-power
driving, it may be due to vapor lock (§I38, 2), malfunctioning of
the antipercolator, which causes excessive richness and will require
adjustment, or overheating of the engine.
§145. Engine
backfires
It is not uncommon for backfiring to occur
in a cold engine, due to a temporarily improper air-fuel-mixture
ratio or to sluggish intake valves. However, after the engine has
started and is warming up, backfiring becomes a more serious matter.
It may be due to an excessively rich or lean mixture which will not
ignite properly, causing backfiring through the carburetor. Backfiring may also be due to preignition caused by such engine conditions as hot valves or excessive carbon, as well as such ignitionsystem conditions as incorrect timing or plugs of the wrong heat
range.
§146. Engine runs but misses If the engine runs but misses, it is
possible that the fuel system is erratic in its action so that fuel
delivery is not uniform. This could result from clogged fuel lines,
clogged nozzles or circuits in the carburetor, incorrectly adjusted
or malfunctioning float levels or needle, or an erratic fuel pump.
Other conditions that might cause missing include ignition defects
such as incorrect timing or defective plugs, coil, points, cap, condenser, or wiring. The exhaust might be clogged, causing back
pressure that prevents normal air-fuel-mixture delivery to the cylinders. Also, the engine might be overheating, or it might have sticky
valves, loss of compression, defective piston rings, and so on.
§147. Quick
A number of quick checks can be
made that will give a rough idea of whether the various carburetor
circuits are functioning satisfactorily. The results of these checks
should not be considered final. Accurate analysis of carburetor
operation requires the use of an exhaust-gas analyzer and an intake[205]
carburetor checks
Automotive Fuel, Lubricating, and Cooling Systems
§147
manifold vacuum gauge. (See the footnote in §137 for the sparkplug test for an excessively rich mixture. )
1. Float-level adfustment. With the engine running at idling
speed, remove the air cleaner, and note the condition of the highspeed nozzle. If the nozzle tip is wet or is discharging gasoline, the
probability is that the float level is high, causing a continuous discharge of gasoline from the nozzle.
2. Low-speed and idle circuits. If the engine does not idle
smoothly, the idle circuit is malfunctioning. Slowly open the throttle
to give about 25 mph engine speed. If the speed does not increase
evenly and the engine runs roughly through this speed range, the
low-speed circuit is out of order.
3. Accelerator-pump circuit. Open the throttle suddenly and note
whether the accelerator-pump circuit discharges a flow of gasoline
into the air horn. The flow should continue a few moments after
throttle reaches open position. On some carburetors this may be
better observed with the engine not running.
4. High-speed circuit. With the engine running at approximately
25 mph, slowly cover part of the air horn with the hand. The engine
should speed up slightly, since this should cause a normally operating high-speed circuit to discharge more gasoline. The high-speed
circuit is probably working improperly if the engine does not speed
up somewhat.
CHAPTER CHECKUP
The chapter you have been studying is probably one of the most difficult in the book. At the same time it is perhaps the most important. For,
to be an expert automotive mechanic, you need to know how to find
causes of trouble in the engine and fuel system. The fact that you have
come this far in the book indicates that you have made a fine start toward
becoming an expert on fuel systems. The checkup below will help you
find out how well you are remembering what you have been studying on
the subject of trouble-shooting in the fuel system. It will also help you
review the important points and fix them more firmly in your mind. If
any of the questions seem hard, just reread the pages that will give you
the answer.
Correcting Troubles Lists
The puri\ose of this exercise is to help you to spot related and unrelated
troubles I>,lll· a list. For example, in the list, excessive fuel consumption:
\
[206]
'\
! \.
\.
\
Diagnosing Fuel-system Troubles
high speed operation, start and stop operation, high float level, low speed
operation, worn carburetor jets, you can see that low speed operation is
the only condition that would not cause high fuel consumption. Thus, it
does not belong on the list. Any of the other conditions increases fuel
consumption.
In each of the lists, you will find one item that does not belong. Write
down each list in your notebook, but do not write down the item that
does not belong.
1. Engine lacks power: throttle linkage out of adjustment, air leaks into
intake manifold, metering rod or power piston stuck, high-octane
fuel, low Hoat level.
2. Excessive fuel consumption: clogged air cleaner, short-run operation,
high-speed operation, stuck metering rod or full-power piston, idle
speed too low, accelerator-pump check valve stuck open.
3. Poor idle: idle mixture too lean, idle speed too low, loss of engine
compression, engine too hot, accelerator pump inoperative.
4. Engine will not start except when primed: line clogged, fuel pump
defective, carburetor jets clogged, spark plugs defective, filter
clogged.
5. Hard starting with engine warm: choke valve closed, vapor lock,
engine parts binding, cooling-system thermostat stuck, manifold heatcontrol valve stuck.
6. Engine stalls as it warms up: choke valve stuck closed, manifold heatcontrol valve stuck, engine overheating, heavy engine oil.
7. Engine stalls after idling: defective fuel pump, engine overheating,
hot engine valves.
8. Engine stalls after high-speed driving: vapor lock, engine overheating, anti percolator malfunctioning, carbon in engine.
9. Engine backfires: lean mixture, rich mixture, engine overheating, excessive carbon, hot valves, high-octane fuel.
10. Engine runs but misses: fuel-pump action erratic, carburetor jets
clogged, engine overheating, ignition-system defects, excessive rolling
resistance, clogged exhaust.
Completing the Sentences
The sentences below are incomplete. After each sentence there are
several words or phrases, only one of which will correctly complete the
sentence. Write each sentence down in your notebook, selecting the
proper word or phrase to complete it correctly.
1. The fuel-mileage tester measures
per gallon
miles per minute
miles per hour
the fuel pump
miles
[207]
Automotive Fuel, Lubricating, and Cooling Systems
2. Exhaust-gas analyzers test
intake-manifold pressure
fuelpump action
exhaust gases
intake mixture
3. Worn carburetor jets or a clogged air cleaner will cause
fullpower operation
high fuel consumption
spark knock
fast engine warm-up
reduce fuel consumption
4. Excessive rolling resistance will
reduce float-level
reduce idle speed
reduce top speed
height
5. If the engine will not start except when primed, a possible cause is
a
defective choke
defective accelerator pump
defective fuel pump
6. If the engine starts hard when warm, a possible cause is
defective choke
excessive rolling resistance
heavy engine oil
high-octane fuel
7. Slow engine warm-up may be due to
stuck accelerator pump
stuck-fuel pump
stuck choke valve
overlean mixture
B. A smoky, black exhaust is due to
very rich mixture
stuck
heated engine
vapor lock
engine valves
9. Engine stalling after high-speed driving may be due to
vapor
lock
high compression
excessive fuel-pump pressure
excessive rolling resistance
10. Engine backfiring could result from
loss of compression
improper mixture ratio
defective oil
pump
11. Engine missing could be caused by
high compression
high-octane fuel
fuel pump erratic
cause excessive rolling resist12. An excessively rich mixture will
ance
cause fouled spark plugs
increase engine efficiency
damage fuel pump
13. If the high-speed nozzle in the carburetor air horn is discharging
gasoline when the engine is running at idling speed, then probably
the
float level is high
float level is low
fuel line is
clogged
accelerator pump is defective
14. Poor fuel economy means
less high-speed operation
less
fuel-pump pressure
less miles per gallon
less gallons per
mile
15. If the engine stalls after a period of idling, it is probably due to a
defective
oil pump
water pump
fuel pump
air
pump
Trouble-shooting Fuel-system Complaints
The following questions are "stumpers" that you might actually encounter in the automotive shop. That is, as an automotive mechanic, you
[20B]
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Diagnosing Fuel-system Troubles
might come up against complaints of high fuel consumption, loss of
power, engine stalling, and so on, and you would have to know what to
do to find the cause and eliminate it. In the following questions, you are
asked to write down the procedures you would follow if various troubles
were reported to you. If you are not quite sure of a procedure, turn back
to the pages in the chapter that will give you the information. Then write
it down in your notebook. Do not copy, but write it in your own words.
This will help you remember the procedures.
1. A man brings his car into your shop and complains about low gasoline
mileage. He is very impatient and keeps "gunning" the accelerator
while he talks to you. What might you suspect is the trouble? What
other driving conditions increase fuel consumption?
2. How does improper choke action increase fuel consumption?
3. If you suspected that the cause of poor fuel economy was in the
carburetor, what are the things you would look for?
4. What are some of the conditions, not in the fuel system, that might
increase fuel consumption?
5. A man drives his car into your shop and complains that he cannot get
more than about 55 or 60 mph although he used to get 15 or 20 mph
more. What are some of the conditions, in the fuel system, as well as
elsewhere, that you should consider?
6. When an engine will turn over but will not start, what ignition test
can you make? What fuel-system test?
7. You are called out into the country to a stalled car and find that the
engine, when primed, turns over normally and will run. What would
you do then to try and find the trouble?
8. If an engine stalls when it warms up, where would you look for the
trouble?
9. You are called out to bring in a stalled car. The owner tells you that
it had been running all right but when he stopped in the driveway
and left the engine running while he talked some business over with
a prospect, it stalled. There is fuel in the tank, and the engine does
not seem to be overheated. Where would you look for trouble?
10. An engine is backfiring badly. Where would you look for trouble?
11. What are some of the causes of a missing engine?
12. You are called out to bring in a car that will not start. The owner tells
you that he had been out driving all morning and that he came home,
stopped for a moment, and then tried to start. The engine wouldn't
start. However, when you try to start, it starts easily. It took you at
least an hour to get to the car after the owner called you. What do
you think might be the trouble?
13. What is a quick check to determine if the Roat level is too high?
[209]
Automotive Fuel, Lubricating, and Cooling Systems
14. What is a quick chcck of the high-speed circuit?
15. What is a quick check of the accelerator-pump circuit?
SUGGESTIONS FOB. FUHTHEH STUDY
Careful observation of checking and trouble-shooting procedures in an
automotive service shop, plus examination of components and parts that
have caused trouble, will be of great value to you. This will help you link
cause and effect together. For instance, if you can examine a fuel pump
with a cracked diaphragm, you will be able to see why it would not
deliver enough fuel to the carburetor, causing starvation of the engine.
It will be a great asset to you if you know thoroughly the troubleshooting procedures in the chapter. One way of helping yourself remember them, as we have already suggested, is to write the procedures
or the causes and effects down on 3- by 5-inch cards and carry these
cards around with you. At odd moments, as, for instance, when you are
riding on a bus, eating a sandwich, or getting ready for work, you can
take out a card and read it over. Soon ,vou will know the various causes
of excessive fuel consumption or loss of power and other troubles in the
engine and fuel system.
Be sure to talk with expert automotive mechanics and your instructor
about the various methods of locating troubles in engines. Ask them about
their experiences in locating troubles, how often they find loss of power
is due to defects in the fuel system, whether fuel pumps are causing them
much trouble, and so on.
\
9: Fuel-system service
THIS CHAPTER deals with fuel-system service and covers all
fuel-system components except carburetors. Carburetor service is
described in a following chapter (Chap. 10). Special tools are
required to perform many of the fuel-system service jobs. Such
special tools are described on the folloWing pages where the service
jobs are covered. In addition, several common hand tools are
needed. These common hand tools are described in another book in
the McGraw-Hill Automotive Mechanics Series (Automotive Engines). Refer to that book for information on them.
§148. Cleanliness The major enemy of good service work is dirt.
A trace of dirt in the wrong place in a carburetor or fuel pump may
cause serious difficulty. For example, dirt in the needle-valve seat in
the carburetor float bowl may prevent closing of the needle valve;
the float bowl will overfill and cause an excessively rich mixture
and high fuel consumption. Similarly, dirt in the idle circuit or
accelerator-pump system may produce malfunctioning of the carburetor and inferior engine operation. Thus, when you are repairing a
fuel pump or a carburetor, you should be sure that your hands, the
repair bench, and the repair tools are really clean. In addition to
this precaution, there are two other cautions to observe, as follows.
Caution 1: It is often the practice to use an air hose to air-dry
carburetor and fuel-pump parts after they have been washed in
cleaning compound and also to blowout carburetor circuits. When
using an air hose, remember that the air stream drives dirt particles
before it at high velOcity. Such particles could get into the eyes and
injure them. Be very careful where you point the hose. To be on the
safe side, many automotive mechanics wear safety goggles to protect
their eyes when they use the air hose. This is good safety practice
and you should follow it.
[211]
Automotive Fuel, Lubricating, and Cooling Systems
§149
Caution 2: Never forget that gasoline vapor is highly explosive.
Use extreme care in handling fuel-system parts that may be covered
or filled with gasoline. When removing a carburetor, fuel pump,
filter, or fuel tank, drain it into a container and then wipe up all
spilled gasoline with cloths. Put the cloths outside to dry. Never
b1'ing an open flame near gasoline! This could result in a disastrous
fire.
§149. Air-cleaner service The air cleaner (Fig. 9-1) passes a
tremendous amount of air through its filter element. The filter
element constantly removes dirt and dust from tlle air; this dirt
gradually accumulates in the element and clogs it. On the oil-bath
FIG. 9-1. Air cleaner with wing nut
and filter element removed and the
side partly cut away to show oil
level.
type of cleaner, much of this dirt is washed down into the oil so
that the oil gradually becomes dirty. To prevent loss of cleaner
efficiency, the cleaner must be removed from the carburetor periodically and cleaned.
Cleaners are attached by a wing nut clamp, or screw clamp. In
addition, many cleaners have a brace fastened by screws. When
removing a cleaner, hold it level so you do not spill the oil (on oilbath type ). Take off the cleaner wing nut and cap so the filter element can be removed. Wash t..he filter element thoroughly in clean
gasoline or cleaning fluid. After it has dried, dip it in clean engine
oil and set it aside to drain. Then, on the oil-bath type of cleaner,
drain the old oil and wash the cleaner. Scrape off caked dirt. Fill
the oil reservoir to the oil-level mark with oil of the specified grade.
Install the ~lter
element and replace the cap. When reinstalling the
cleaner, hold it level so you do not spill the oil.
[212]
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§151
Fuel-system Service
§150. Manual-choke adjustment
On manual chokes, a choke button
on the dash is linked through a control wire in a conduit to the
choke valve in the carburetor (Fig. 9-2). If the wire slips in the
screw clamp or if it kinks, the choke valve may not open and close
properly as the choke control is moved in and out. It is a simple
operation to loosen the screw clamp and slide the wire one way or
the other to get proper adjustment. With the choke button in, the
choke valve should be open. With the choke button pulled out, the
choke valve should be closed. Kinks may be straightened by bend-
CHOKE WIRE COIiOUIT CLAMP
CHOKE BUTTON PUSHED • Itt •
FIG. 9-2. Linkage to choke valve in carburetor.
ing the wire. Sometimes the conduit supports are bent out of line,
causing the wire to bind inside the conduit. The supports should be
straightened. If the wire still binds, put a few drops of penetrating
oil along the conduit. It will penetrate to the wire and lubricate it.
§151. Automatic-choke adjustment
Automatic chokes, or climatic
controls, are of two general types. One type, electrically operated,
is mounted on the exhaust manifold and is linked by a rod to the
carburetor choke valve (Fig. 9-3). Other types are mounted on
the carburetor (Fig. 9-4). See also §72 for other illustrations of
automatic chokes.
1. Elect1·ic choke. To adjust the type of choke shown in Fig. 9-3,
remove the air cleaner and open the throttle enough to release the
[213]
§151
Automotive Fuel, Lubricating, and Cooling Systems
fast-idle cam. Then close the choke valve by hand, or pull on the
control rod until the hole in the choke control shaft and the notch in
the choke control base align. Insert the adjusting tool as shown to
hold the control in this position. Now, loosen the clamp screw on
the choke lever, and move the lever until the choke valve is tightly
closed. Hold the choke valve closed, and tighten the clamp screw.
2. Hot-ai1' choke. To adjust the type of choke shown in Figs.
FIG. 9-3. Adjustment of manifold-mounted automatic choke. 1, carburetor
choke valve; 2, choke-lever clamp screw; 3, adjusting tool. (Chrysler Sales
Division of Chrysler Corpo-ration)
4-20 or 9-4, loosen the two or three cover clamp screws and tmn
the cover one way or the other to obtain a richer or leaner warm-up
mixtme. On the type of choke shown in Fig. 9-4, the heat-tube
coupling must be loosened before the adjustment is made. Adjustment should be made one notch at a time. When adjustment is
correct, the choke valve should move to the fully opened position
as the engine warms up and reaches operating temperature. With
the adjustm-vnt complete, tighten the clamp screws and, on the
choke shown in Fig. 9-4, tighten the heat-tube coupling.
[214]
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§151
Fuel-system Service
/
Carbllretor
FIG. 9-4. Adjustment of automatic choke.
MARK ON PISTON PLATE
HOUSING
CHOKE VALVE SHAFT
CARBURETOR
HE" TUSE FRO• •
ANIF"_~
9-5. Heat tube and cover detached from automatic choke so screen can
be seen.
FIG.
[215]
§155
Automotive Fuel, Lubricating, and Cooling Systems
from a hammer blow might set off vapor remaining in the tank with
a terrific explosion.
The fuel filter in the tank (where present) can be cleaned, if the
tank is removed, by blOwing air through it from an air hose. Air
should be directed through the filter from the fuel outlet.
When replacing a tank, make sure that the supports are firmly
fastened. Also clean the fuel-gauge terminals well so that good
contact will be made when the wires are connected.
FLARED END OF
'II:. .," '"
FERRULE COMPRESSES ON PIPE
WHEN NUT IS TIGHTENED
FITTING
o
FLARED TYPE
SLEEVE SWEATED ON PIPE
~,u
COMPRESSION TYPE
BEVELED END OF NUT
COMPRESSES ON
~'"
.
SOLDERED TYPE
FIG.
NUT
COMPRESSION NUT TYPE
9-7. Various types of fuel-line couplings or fittings.
§ 155. Fuel lines Fuel lines (or pipes, or tubes, as they are also
called) are attached to each other and to the carburetor, fuel pump,
and tank by means of different types of coupling (Fig. 9-7). When
loosening a coupling of the type having two nuts, use two wrenches
as shown in Fig. 9-8 in order to avoid twisting the line and pOSSibly
damaging it.
When installing a new line of the flared type, it is best to doubleflare the tube as shown in Figs. 9-9 and 9-10. This double flaring
assures a safer and tighter connection. One type of tool used to
double-flare' tubes is shown in Fig. 9-11. The tube is first cut off
square anq the cuttings cleaned out of the tube. Then the tube is
[218]
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§155
Fuel-system Service
inserted into the tool the proper depth, and the "first-flare" forming
tool is driven against the tube to form it as shown in Fig. 9-9. Next
the other forming tool is used to drive the flare on down so that
the double flare is formed, as shown in Fig. 9-10.
Wrenches to fit snugly
on nut ond on fiffing
FIG. 9-8. Method of using two
wrenches to loosen or tighten coupling
nuts and thereby avoid twisting and
damaging the line.
FIG. 9-9. Making the first Bare.
(Kent-Moore Organization, Inc.)
FIG. 9-10. Final Baring operation.
(Kent-Moore Organization, Inc.)
Fuel lines should be adequately supported at various points
along the frame. If a line is rubbing against a sharp corner, it should
be moved slightly to avoid wear and a possible leak. Fuel lines must
not be kinked or bent unnecessarily since this treatment is apt to
cause a crack and a leak.
If the fuel line between the pump and tank is thought to be
clogged, it may be tested by disconnecting the line at the pump
and applying an air hose to it. Remove the tank filler cap. Do not
apply too much air since this might blow gasoline out of the tank.
[219]
Acc: .....
Date:
§156
Automotive Fuel, Lubricating, and Cooling Systems
If the line will not pass air freely, it could be clogged with dirt; or
perhaps it has become badly kinked or pinched at a bend or
support. Also, on tanks with an internal filter, the filter may have
become clogged, although this is extremely rare. Kinked or pinched
lines should be replaced since the kinked or pinched place, even if
straightened, may ultimately crack open and leak.
FIG. 9-11. Tube-flaring tool. (Kent-Moore Organization, Inc.)
§156. Fuel gauges There is very little in the way of service that
fuel gauges require. Defects in either the dash unit or the tank unit
usually require replacement of the defective unit. However, on the
type of gauge that makes use of vibrating thermostatic blades (§38),
dirty contact points, which may cause fluctuations of the needle can
be cleaned by pulling a strip of clean bond paper between them.
Be sure that no particles of paper are left between the points. Never
use emery cloth to clean the points since particles of emery will
embed in the points and cause very erratic gauge action.
If a fuel gauge is defective or malfunctioning of the gauge is
suspected, substitute a new tank unit for the old one. This can be
done without removing the old tank unit, by disconnecting the
tank-unit t~n\ial
lead from the old unit and connecting it to the
[220J
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Fuel-system Service
§156
terminal of the substitute unit. Then connect a lead from the frame
of the substitute unit to any convenient grounding place on the car
in order to assure good grounding of the unit. With these connections made, turn on the ignition switch and operate the float arm of
the substitute unit. If the dash unit now works and indicates as the
float arm is moved up and down, then the old tank unit is defective.
If the dash unit still does not work, then either it is at fault or else
the wiring is defective.
NOTE: On the thermostatic type of fuel gauge, it takes a minute
or so for the thermostats to heat up and start the dash unit indicating. Therefore, on these, wait for a minute or so after turning on
the ignition switch.
CHECK YOUR PROGRESS
Progress Quiz 7
Here is your chance to check up on the progress you have been making
since you started Chap. 9. The questions below will help you review the
material you have just covered and will also fix the more important points
more firmly in your mind. If any of the questions stump you, reread the
pages that will give you the answer.
Completing the Sentences
The sentences below are incomplete. After each sentence there are
several words or phrases, only one of which will correctly complete the
sentence. Write each sentence down in your notebook, selecting the
proper word or phrase to complete it correctly.
1. When servicing an air cleaner, the filter element should be
replaced
washed in oil
washed in cleaning fluid
2. In the manual choke, when the choke button on the dash is pulled
all the way out, the choke valve should be
closed
nearly
closed
open
3. To adjust the hot-air choke to get a richer or leaner warm-up mixture, the
control wire must be adjusted
cover must be
turned
adjusting screw must be turned
4. Generally speaking, the automatic choke, if properly adjusted to start
with,
will require adjustment once a month
will require adjustment once a year
will not get out of adjustment
5. Automatic chokes
should be lubricated monthly
should
be lubricated yearly
should be lubricated with light oil
do not require lubrication
[221]
~ 1 57
Automotive Fuel, Lubricating, and Cooling Systems
6. A fuel line that is kinked or pinched should be
straightened by
hand
replaced
straightened with light hammer blows
7. As a general rule, a defective fuel-guage unit can be readfusted
can be rewired
should be replaced
8. Location of trouble in a fuel-gauge system can usually be determined
by temporarily substituting
a new tank unit
a new dash
unit
new wiring
§157. Fuel-pump inspection The fuel pump can be checked for
pressure, capacity, or vacuum with special gauges as already explained (§§129 to 131). The vacuum pump of the combination
pump can also be tested with the vacuum gauge. Readings obtained
should be compared with the specifications issued by the manufacturer for the model of pump being tested. A rather rough test
of fuel-pump action can be made by loosening or disconnecting
the fuel line from the carburetor and then cranking the engine.
Ignition should be off or the lead from the ignition coil high-tension
terminal grounded so that the engine does not start. During cranking, the fuel pump should deliver a spurt of gasoline with each
rotation of the engine camshaft. Have a container ready to catch
the gasoline, and wipe up any spilled gasoline with cloths and put
the cloths outside to dry.
In addition to checks of the operating action, the fuel pump
should be checked for leaks. Leaks might occur at fuel-line connections or around sealing gaskets, as, for instance, at the joint
between the sediment bowl and the cover or at the joint between
the cover and the pump body.
1. Vacuum-pump test. As mentioned above, vacuum-pump action can be checked with the vacuum gauge. With the vacuum
gauge connected to the vacuum side of the pump, the vacuum developed should be within the specifications of the manufacturer. A
quick check of the vacuum-pump action can be made by turning
on the windshield wipers with the engine running and then accelerating the engine quickly. If the windshield wipers continue to
operate at about the same speed, the vacuum pump is probably all
right. However, if the wipers slow down considerably or stop when
the engine is accelerated, the vacuum-pump diaphragm is probably
cracked or broken. This is a bad situation, not so much from the
standpoint O.f windshield-wiper failure during acceleration, but
because oil can pass through the crack and into the engine COffi[222]
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Fuel-system Service
§158
bustion chambers. This, in turn, produces excessive oil consumption
and all the engine aihnents associated with it (see §227).
NOTE: Windshield wipers will not work as well on dry windshields as on wet windshields. Throw water on the windshield if
you want to see how the wipers will perform under actual driving
conditions.
2. Cleaning sediment howl. The sediment bowl should be
checked for accumulated water and dirt. Water and dirt should be
flushed out by removing the bowl. The bowl is removed by loosening the nut on the bailing wire and pulling the wire to one side.
While the bowl is off, the filter screen can also be cleaned with
cleaning fluid and compressed air. When the bowl is replaced, the
nut should be pulled up tightly so that leakage cannot occur around
the bowl gasket. If the gasket is at all damaged, a new gasket
should be used.
3. Conditions requiring pump removal. If the fuel pump pressure
is too high or too low, if the pump does not deliver fuel normally to
the carburetor, if leaks show up, if the pump has a cracked diaphragm or other defect, or if the pump is noisy, then the pump
should be removed for repair as explained in following sections.
The following section describes various pump troubles and their
causes.
§158. Fuel-pump
The trouble-shooting chart in Chap. 8
lists various fuel-system troubles and their causes. Some of these
causes may lie in the fuel pump; many of them are in the other
fuel-system or engine components. Fuel-system troubles that might
be caused by the fuel pump are discussed below.
1. Insufficient fuel delivery. This could result from low pump
pressure, which in turn could be due to any of the following:
troubles
a. Broken, worn-out, or cracked diaphragm.
h. Improperly operating fuel-pump valves.
c. Broken diaphragm spring.
d. Broken or damaged rocker arm.
e. Clogged pump-filter screen.
f. Air leaks into sediment bowl due to loose bowl or worn gasket.
In addition to these causes of insufficient fuel delivery due to
conditions within the pump, many other conditions outside the
[22.3]
Automotive Fuel, Lubricating, and Cooling Systems
§158
pump could prevent delivery of normal amounts of fuel. These are
listed and described in detail in Chap. 8 and include such things
as a clogged fuel-tank-cap vent, clogged fuel line or fil~er,
air leaks
into the fuel line, and vapor lock. Of course, in the carburetor, an
incorrect float level, clogged inlet screen, or malfunctioning inlet
needle valve would prevent delivery of adequate amounts of fuel
to the carburetor.
2. Excessive pump pressure. High pump pressure will cause delivery of too much fuel to the carburetor since the excessive
pressure will tend to lift the needle valve off its seat so that the
fuel level in the float bowl will be too high. This results in an
overrich mixture and excessive fuel consumption. Usually, high
pump pressure would result only after a fuel pump has been removed, repaired, and replaced. If a fuel pump has been operating
satisfactorily, it is hardly likely that its pressure would increase
enough to cause trouble. High pressure could come from installation
of an excessively strong diaphragm spring or from incorrect reinstallation of the diaphragm. If the diaphragm is not flexed properly
when the cover and housing are reattached, it will have too much
tension and will produce too much pressure. There is more on
this pOint in the fuel-pump reassembly procedures that follow.
3. Fuel-pump leaks. The fuel pump will leak fuel from any pOint
where screws have not been properly tightened and also where the
gasket is damaged or incorrectly installed. If tightening screws does
not stop the leak, then the gasket or diaphragm will require replacement. Note also that leaks may occur at fuel-line connections
which are loose or improperly coupled.
4. Fuel-pump noises. A noisy pump is usually the result of worn
or broken parts within the pump. These include a weak or broken
rocker-arm spring, worn or broken rocker-arm pin or rocker arm,
or a broken diaphragm spring. In addition, a loose fuel pump or
a scored rocker arm or cam on the camshaft may cause noise. Fuelpump noise may sound something like engine-valve tappet noise
since its frequency is the same as camshaft speed. If the noise is
bad enough, it can actually be "felt" by gripping the fuel pump
firmly in the hand. Also, careful listening will usually disclose that
the noise is originating in the vicinity of the fuel pump. Tappet
noise is usually distributed along the engine, or is located more
distinctly iI\ the valve compartment of the engine.
[224]
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§160
Fuel-system Service
§159. Fuel-pump removal As a first step in removing the fuel pump,
wipe off any dirt or accumulated grease so that dirt will not get
into the engine. Then take off heat shield (where present), and
disconnect the fuel lines (Fig. 9-8) and vacuum-pump lines (on
combination pump). Remove attaching nuts or bolts, and lift off
pump. If it sticks, work it gently from side to side, or pry lightly
under the mounting flange with a screw driver to loosen it. Do
not damage the flange or attaching studs. On engines using a push
rod to operate the fuel pump, remove the rod so that it can be
examined for wear or sticking.
§160. Fuel-pump
Many automotive
service departments do not attempt to disassemble and repair fuel
pumps because pump manufacturers have arranged a special pumpexchange program. The old pumps can be traded in on new or
factory rebuilt units. For those who prefer to repair fuel pumps,
special repair kits are supplied. These repair kits contain diaphragms, valves, springs, and gaskets. For combination pumps,
three separate repair kits may be provided: a vacuum-pump
diaphragm kit, a fuel-pump diaphragm kit, and an overhaul kit.
The vacuum-pump diaphragm and fuel-pump diaphragm kits contain only the diaphragm, valves, springs, and gaskets needed to
repair the vacuum or the fuel pump. The overhaul kit includes
everything in both kits plus links and other parts that might wear.
Thus, it can be seen that repair of a fuel pump may require replacement of nearly all the parts in it. Figure 9-12 shows an overhaul kit for a combination pump.
Disassembly procedures for fuel pumps vary somewhat according
to their construction. Generally speaking, there are two types of
pumps, the fuel pump and the combination fuel and vacuum pump;
thus there are two general disassembly procedures. Regardless of
the procedure, the first step is to clean the outside of the pump
thoroughly to remove all dirt, grease, or oil. A simple way of doing
this is to plug the pump openings, wash the outside of the pump in
cleaning solvent, and then blow it dry with an air hose. Next the
fuel body and cover or covers should be lightly scratched with a
sharp knife or file so that their original relationship is established.
These marks should be realigned on reassembly. After this, the
disassembly procedure may begin.
[225]
disassembly
and
assembly
Automotive Fuel, Lubricating, and Cooling Systems
§1 61
Fuel diaphragm
Vacuum
diaphragm
Link
Link~
""
"
Pin'! r ~
se::(?) X
Rerot, ,
~
A
6 n
\rm
Screws
Retainer
Gaskets
o
0
o
/
oS °0
Q
()
~seOJ
Screen
Valves
9-12. Repair kit for a combination fuel and vacuum pump. (Ford Motor
Company )
FIG.
§161 . Fuel-pump disassembly and reassembly, type 1 Figure 9-13
is a sectional view and Fig. 9-14 a disassembled view of one type of
fuel pump which may have either a glass Or a metal sediment bowl.
Disassembly is as follows:
1. Take off sediment bowl and strainer.
2. Remove cover screws and lock washers so body and cover
can be separated. Do not pry between flanges with a screw driver
if parts stick, as this would damage the sealing faces. Instead, tap
them apart with the handle of a screw driver or a plastic hammer.
S. Take out valve-retainer screw, and remove retainer and
valves. Note carefully the locations of the valves so that they may
be returned to their proper ports.
4. Push 4t on center of diaphragm so the diaphragm stem can
be unlinked.. from the inner rocker-arm link.
5. Drive out rocker-arm pin if it is necessary to remove the
rocker arm.
[226]
\.
\
Fuel-system Service
FIG. 9-13. Sectional views of a fuel pump. The
diHerent sectional views were made to show the
diaphragm (top ) and the valves (bottom) .
(Plymouth Division of Chrysler Corporation)
§161
9-14. Disassembled
view of fuel pump in Fig.
9-13. (Plymouth Division
of Chrysler Corporation)
FIG.
6. If the oil seal (which fits around the diaphragm stem) is
damaged, it may be removed from the body by chipping off the
pieces of the housing holding it in place and then driving it out.
The new oil seal should be staked to the housing with a hammer
and diamond-point chisel.
7. After disassembly, all parts should be washed in kerosene
or gasoline. Any damaged parts should be discarded and new
parts used on reassembly. Usually this means obtaining an overhaul
kit.
8. Reassembly is practically the reverse of disassembly. All parts
must be clean, and the new diaphragm should be soaked in kerosene
or gasoline.
[227]
Automotive Fuel, Lubricating, and Cooling Systems
§162
9. Valves should be installed in the cover in the exact positions
as on the original unit. Tighten retainer screw.
10. Insert diaphragm stem through oil seal, and insert rockerarm link into slot in stem.
11. Attach cover and diaphragm to body with screws and lock
washers. Leave all screws quite loose, and then hold rocker arm
to end of its stroke tight against spring pressure while screws are
tightened. This seats diaphragm properly with the correct flexing.
Caution: Do not use sealing compounds such as shellac on the
diaphragm.
12. Attach sediment chamber.
13. Rough-test the pump by connecting rubber hose at the two
pump couplings. Then insert the inlet hose in a container of gasoline, and work the rocker arm. Fuel should spurt out of the outlet
hose with every stroke of the arm.
§162. Fuel-pump disassembly and reassemby, type 2 Figure 3-7
shows a second type of fuel pump which is similar to the one shown
in Fig. 9-13 but which requires a slightly different disassembly and
assembly procedure.
1. Take off sediment bowl and screen.
2. Remove top cover screws and cover. Do not pry the cover
off if it sticks, since this would damage the sealing faces. Instead,
tap the cover off with a plastic hammer or the handle of a screw
driver.
3. Raise the edge of the diaphragm so that a thin-bladed screw
driver can be inserted. With the screw drive~
lift the spring body
and oil seal off the boss in the fuel-pump body, and slide it to one
side.
4. Unhook the diaphragm stem from the rocker-arm link by
pressing down on the diaphragm and tilting it away from the rocker
arm.
5. Remove oil seal and retainer from diaphragm stem.
6. Remove valve retainers and valves. Note positions of valves
carefully so that valves can be restored to original positions.
7. Wash all parts in cleaning solvent, and discard defective
parts. U se\ overhaul kit with new parts in it. Soak new diaphragm
in gasoline before installing it.
[228]
\\
\
\
\
\
'\
Fuel-system Service
§163
8. Assemble oil seal on diaphragm stem. Put oil-seal spring on
first, followed by upper retainer, two leather seals, and., lower
retainer with convex part, or cup, out.
9. Raise the rocker-arm link with a screw driver as shown in
Fig. 9-15, and, with the diaphragm spring in place, hook the link
into the diaphragm stem. Then slide the diaphragm and seal as~
sembly over lmtil the seal drops down over the boss on the body.
10. Install valves with retainer and gaskets.
9-15. Hooking fuel-pump link to diaphragm stem with screw driver.
(Chevrolet Motor Division of General M_0tors Corporation)
FIG.
11. Attach the cover and body with screws and lock washers,
making sure that the diaphragm is seated and flexed while the
screws are tightened.
12. Attach screen and sediment bowl.
13. Test as noted in §161, 13.
§163. Combination fuel- and vacuum-pump disassembly and reasFigure 9-16 is a sectional view of one type of combination fuel and vacuum pump which has the fuel pump above and
the vacuum pump below. Figure 9-17 is a disassembled view of a
similar unit. Both the vacuum and the fuel pumps operate from
the same rocker arm. Disassembly and reassembly procedures
sembly, type 1
follow.
f229)
§163
Automotive Fuel, Lubricating, and Cooling Systems
1. To disassemble the fuel pump, first take off the sediment
bowl and screen.
2. Take out cover attaching SCl'ews and lock washers, and lift
off cover.
3. Note pOSitions of valves, and then remove retainer screw,
retainer, and valves.
INLET
"a"
INTAKE MANIFOLD
EXHAUST VALVE "P"
FIG. 9-16, Sectional view of combination fuel and vacuum pump. (Ford Motor
Company)
4. Press diaphragm down at center and tilt it to one side, away
from rocker arm, so that rocker-arm link can be withdrawn from
slot in diaphragm stem.
5. Ta,ke off diaphragm with oil-seal parts (including spring,
washers and, retainers) .
.\
6. To d~saembl
the vacuum pump, take out two cover screws
\
[230]
t\
\
\
\
Fuel-system Service
§163
and substitute two long screws for them, turning the long screws
all the way in. Then take out the other screws. Now, loosen the
two long screws little by little to relieve the vacuum-pump spring
pressure. When the pressure is relieved, take out the screws and
take off the cover.
BOW/~
N"'-----ffi=::
~Scren
GOsket~
cover~
..
~
-
o
~:e
° :
Retainer--f
®
Gasket
Arm"
Link
~\:O
~"'
,~o
@r#»
c~l g
:
~
@
Adaptor
Gasket
Body---
~ ~O"PNro'm
Retainr-+:~,
Gl
@
© ,0
o __
~
\:/(~,
Cal/er
,
-,
• ®
O~P/ate
.c::.Jr-- GClsket
,
®
FIG. 9-17, Disassembled view of combination fuel and vacuum pump. (Ford
Motor Company)
7. Remove valves by taking off retainer. Note positions of valves
so they can be replaced in proper positions.
8. Unlink diaphragm stem from rocker-arm link.
9. Replace oil seal through which vacuum-pump diaphragm
stem moves, if it is defective.
10. Wash all parts in cleaning solvent, and discard defective
[231]
§164
Automotive Fuel, Lubricating, and Cooling Systems
parts. Use overhaul kit with new parts for reassembly. Soak new
diaphragms in gasoline before installing them.
11. To reassemble vacuum pump, install valves and retainer.
Put vacuum-pump diaphragm on body, and link diaphragm stem
to rocker-arm link. Then put diaphragm spring in place, and use
two long screws to compress spring and bring vacuum-pump cover
into position on body. Install attaching screws and lock washers,
and then remove long screws so that the last two attaching screws
can be put into place.
12. Reassemble the fuel pump by installing valves and retainer.
Put oil-seal parts on diaphragm stem, and place diaphragm on pump
body. Attach link to diaphragm stem, and then attach fuel-pump
cover to body with screws. Have diaphragm flexed when screws
are tightened in order to make sure that the diaphragm is not
creased and will not have excessive tension.
13. Test fuel pump as in §161, 13. Vacuum pump cannot be
tested with pump off the car without special equipment, but it can
be tested after installation as explained in §157.
§164. Combination fuel- and vacuum-pump disassembly and reassembly, type 2 Figures 9-18 and 9-19 are disassembled views of
combination pumps which have the fuel pump below and the
vacuum pump above. Both fuel and vacuum pumps operate from
the same rocker arm. Disassembly and reassembly procedures
follow.
1. Remove vacuum cover by taking out two screws and substituting two long screws for them. Turn these screws in tight. Then
take out other cover screws, and gradually back off long screws to
relieve diaphragm-spring tension slowly. Then turn pump so that
vacuum diaphragm is down, and push up on diaphragm, tilting
diaphragm stem to one side so that the rocker-arm link is unlinked
from the stem. Take off diaphragm, and remove oil-seal spring,
seal, and retainers from stem.
2. Remove valves from vacuum-pump cover after noting their
positions.
3. Remove fuel cover by taking out attaching screws and lock
washers. Take valves out of cover after noting their positions. To
remove the '.?iaphragm, it must be detached from the rocke~am
link, and the best way to do this without damaging the oil seal is
[232]
Fuel-system Service
§164
to drive out the rocker-arm pin with a punch and hammer. Then
the link may be detached from the diaphragm stem.
4. Remove the diaphragm by draWing it straight out of the oil
seal. Tilting it is apt to damage the seal, and this would require
installation of a new seal.
~
~
Stud
_ _ Cover
~GOSket
-t
-
T! ~r-
Vacuum
cover
"Ji't
;;;"t-~J-
Valve
assembly
~Spring
~p,n
Spring
F,Yter
U
~.
.
c.
Arm
_.
4
~ ~.
' Jf':.~
~h
J.... . .
...
' '
c
Spring
.
(Ink
Body
(
, ~-Spng
-r~Rod
~O,ophr.gm
r......
i-J
Valve
.
assembly
_ _ _ Fuel cover
.Screen
"'__Gosket
O'
r
_, J - B a w /
Seat
-~
~
\,e. ...
Boil assembly
Nut .
FIG. 9-18. Disassembled view of combination fuel and vacuum pump. (Plymouth Division of Chrysler Corporation)
5. A new oil seal should be installed if the old one is damaged.
The old one can be removed with a driver or special puller. The
new one is then installed and snugged, or staked, into place with
a special tool.
6. Mter all parts are removed, they should be cleaned in clean[233]
§164
Automotive Fuel, Lubricating, and Cooling Systems
ing solvent, and defective parts should be discarded. An overhaul
kit will supply the new parts. Soak new diaphragm in gasoline or
kerosene before installation.
NOTE: On some models the overhaul kit includes a fuel diaphragm gasket to compensate for any slight warpage of the fuel
cover and assure a tight jOint between the cover and body.
Cork Go,ket
Val...
Pull Rod
1
!
'~.7I L~k ':.~ , ~q:
Bd
Pm
G Q ~k e l"
Y
"'. ;
............. _- __ Pin
I
,;;t
Fuel D,a phragm
Sprjng
f\
YacVtJIlI link -~.
(_~
: (~· ~ :~~ ~ ! c~~f _; ~ ~
Valve
Gosket
I ::::::..--'"
Gasket
\
Bail
Screen
; ; ; Fue l link
J
ROCk::'::: ~
0
Seal Pull Rod
Fuel D,aphrogm
Spnng
: : :rn
Fuel Pum p 5id e
5pring
J"'_ vocvum LinJc
Wo,he-I
FIG. 9-19. Disassembled view of combination fuel and vacuum pump. (Cadillac Motor Car Division of General Motors Corporation)
7. The fuel pump should be reassembled first. Put valves in
cover (or fuel body) , and fasten them with retainer. Place retainer and spring on diaphragm rod, and insert diaphragm rod
straight into oil seal in body. A special tool may then be necessary
to attach link to the diaphragm stem, after which the rocker-arm
a~sembly
can be attached with the arm pin. The end of the pin
should be peened over to prevent its loosening.
8. With the diaphragm in place, attach the fuel cover to the
body with ' ~crews
and lock washers. Run the screws up loosely,
and then make sure that the diaphragm is centered and fully
[234]
\
§165
Fuel-system Service
flexed. Then tighten the screws. Do not tilt diaphragm during reassembly as this might damage the oil seal.
9. Assemble the vacuum pump by installing the valves with retainer. Then put diaphragm, with oil-seal parts, in place on body,
and tilt it so that rocker-arm link can slip into slot in diaphragm
stem. Put spring in place, and attach cover with two long screws,
running the screws down evenly to draw cover down and compress
spring. Install other screws, remove two long screws, and put
regular screws in their place.
10. Test fuel pump as in §161, 13. Vacuum pump cannot be
tested off the engine without special equipment, but it can be
tested after installation as explained in §157.
§165. Fuel-pump installation Make sure that the fuel-line connections are clean and in good condition. Connect the fuel and
vacuum lines to the pump before attaching the pump to the engine.
Then place a new gasket on the studs of the fuel-pump mounting
or over the opening in the crankcase. The mounting surface of the
engine should be clean. Insert the rocker arm of the fuel pump
into the opening, making sure that the arm goes on the proper side
of the camshaft (or that it is centered over the push rod). If it
is hard to get the holes in the fuel-pump flange to align with
the holes in the crankcase, turn the engine over until the low side
of the camshaft eccentric is under the fuel-pump rocker arm. Now
the pump can be installed without forcing or prying it into place.
Attach with bolts or nuts. Check pump operation as explained in
§157.
CHECK YOUR PROGRESS
Progress Quiz 8
Once again you can check your progress in the book. The following
quiz covers fuel-pump servicing procedures as described in the second
half of the chapter. The questions will serve as a review of the important
points covered in the chapter and will help you to remember them.
Completing the Sentences
The sentences below are incomplete. After each sentence there are
several words or phrases, only one of which will correctly complete the
sentence. Write each sentence down in your notebook, selecting the
proper word or phrase to complete it correctly.
[235]
Automotive Fuel, Lubricating, and Cooling Systems
1. To quick-check the fuel-pump action, loosen or disconnect fuel line
from carburetor
with engine running at medium speed
with engine idling
and then crank the engine
2. If the vacuum-pump diaphragm is cracked or broken, accelerating
the engine quickly will cause the windshield wipers to
speed
up
stop
slow down very little
3. A cracked vacuum-pump diaphragm will allow oil to pass through
the crack and cause
an oily windshield
excessive oil consumption
excessively fast wiper action
4. A broken diaphragm or spring, stuck valves, clogged screen, or air
high pump pressure
low
leaks in the fuel pump can cause
pump pressure
high float level
rich mixture
5. A high fuel level in the float bowl and an excessively rich mixture
high pump pressure
could result from
low pump pressure
a cracked diaphragm
CHAPTER CHECKUP
NOTE: Since the following is a chapter review test, you should review
the chapter before taking the test.
You are now well into the part of the book that gives you practical
guidance in actual shopwork on automotive fuel systems. Sample servicing procedures on the various fuel-system components are covered on
these pages. You should have a good idea of how to service these components, and for this reason step-by-step procedures on several models of
components are included. As you study these procedures, you will learn
the important details of fuel-system service. The following chapter review
test gives you a chance to find out how well you have remembered the
essential points covered in the chapter.
Completing the Sentences
The sentences below are incomplete. After each sentence there are
several words or phrases, only one of which will correctly complete the
sentence. Write each sentence down in your notebook, selecting the
proper word or phrase to complete it correctly.
1. To prevent loss of air-cleaner efficiency, the filter element must be
removed from the cleaner periodically and
thrown away
cleaned
blown out with compressed air
2. With the adjusting tool holding the electric choke control in position,
tightly closed
wide open
the choke valve should be
half open
3. To adjust the hot-air choke, loosen the two or three cover clamp
screws and turn the
clamp
carburetor
choke valve
cover
[236]
Fuel-system Service
4. If a fuel tank is to be repaired, great care must be used to make sure
it is absolutely free of
water vapor
attaching studs
gasoline vapor
fuel-gauge wires
5. Double flaring the fuel-line tube assures
shorter tubing
a safer and tighter connection
stiffer tubing
longer tubing
6. To locate trouble in a fuel-gauge system, temporarily substitute for
the old unit a
new dash unit
new wire
new tank
unit
new switch
7. A quick check of vacuum-pump action can be made by turning on
the windshield wipers and then
stopping the engine
starting the engine
accelerating the engine
turning off
the wipers
8. A broken fuel-pump diaphragm spring, improperly operating pump
valves, broken diaphragm, clogged screen, or air leaks could cause
high fuel-pump pressure
fuel-tank stoppage
insufficient
fuel delivery to carburetor
9. An excessively strong fuel-pump diaphragm spring or an improperly
installed diaphragm could cause
insufficient fuel delivery
high pump pressure
fuel-gauge reading
loose connections
10. Before they are installed, new diaphragms should be
hot
soaked in gasoline
stretched
cold
Service Procedures
In the following, you should write down in your notebook the procedures asked for. Do not copy the procedures from the book, but try to
write them in your own words. Give a step-by-step account of how to
do the service job asked for. This will help you remember the procedures
later when you go into the automotive shop. If possible, get hold of
various fuel pumps and instruction manuals on fuel pumps. Study them,
and base your write-ups on them instead of those covered in the book.
This will give you a wider experience in fuel pumps.
1. Explain how to adjust a manual choke.
2.
3.
4.
5.
6.
7.
Explain how to adjust an electric choke.
Explain how to adjust a hot-air choke.
Explain how to remove and replace a hot-air choke.
Explain how to remove and replace a fuel line.
Explain how to check a defective fuel-gauge system.
Explain how to check a fuel pump for pressure, capacity, and
vacuum.
8. Explain how to quick-check a fuel pump.
9. Explain how to check a vacuum pump by using the windshield
wipers.
[237]
Automotive Fuel, Lubricating, and Cooling Systems
10. List conditions that would require fuel-pump removal.
11. List conditions in the fuel pump that could cause insufficient fuel
delivery.
12. List conditions outside the fuel pump that could cause insufficient
fuel delivery.
13. List causes of excessive fuel-pump pressure.
14. Explain how to remove a fuel pump from an engine.
15. Explain how to disassemble and reassemble a fuel pump.
16. Explain how to disassemble and reassemble a combination fuel and
vacuum pump.
17. Explain how to install a fuel pump on an engine.
SUGGESTIONS FOR FURTHER STUDY
When you are in the automotive shop, keep your eyes and ears open so
that you can learn more about how the various fuel-system jobs are done.
Study any carburetor and fuel-pump manuals you can lay your hands
on. Carefully examine any carburetors and fuel pumps you can. If the
shop has some old or defective units, perhaps you can borrow them so
that you can practice disassembling and reassembling them. The more
practice you can get in handling the small parts that go into these units,
the better. If you can find particular model fuel pumps and the fuelpump manuals that apply to them, study the manuals carefully and then
follow the step-by-step procedures in disassembling and reassembling
the pumps. Write down in your notebook any important points, or even
whole procedures, on these service operations. You will find that writing
these facts down will help you remember them. At the same time, you
will find that your notebook is becoming an increasingly valuable reference for you.
f2381
10: Cal'bul'etol' service
THIS CHAPTER continues the discussion of fuel-system service
and covers the disassembly, repair, reassembly, and adjustment of
carburetors. Carburetor service requires a number of special tools,
and their use is described on following pages where the servicing
jobs are covered. In addition, several common hand tools are
needed. These common hand tools are described in another book
in the McGraw-Hill Automotive Mechanics Series (Automotive
Engines). Refer to that book for information on them.
§166. Cleanliness It is extremely important to keep carburetor
parts and circuits as clean as possible. Bits of dirt or dust that are
allowed to get into the carburetor will probably cause carburetor
and engine trouble sooner or later. The jets or nozzles and circuits
through which gasoline flows are carefully calibrated to within
thousandths of an inch. Dirt or gum that changes this calibration
will have a marked effect on carburetor and engine performance.
On the other hand, careless cleaning of the nozzles or jets may
enlarge them slightly, resulting in overrichness, fuel waste, and
excessive carbon in the engine with all its attendant ills.
The two general cautions about use of the air hose, and the explosiveness of gasoline vapor, contained at the end of §148, also
apply in regard to carburetor service. Reread those cautions now.
Heed them at all times when working in the automotive shop.
§167. Carburetor
Various carburetor troubles are outlined
in detail in Chap. 8; the trouble-shooting chart lists the various
causes of the different complaints that might arise from malfunctioning of the carburetor or other fuel-system component. In
the carburetor, such conditions as incorrect fuel level in the float
bowl, incorrect idle-speed and idle-mixture adjustments, clogged
idle or high-speed circuit, or malfunctioning accelerator-pump
system can cause trouble. QUick checks of these various circuits
are outlined in §147.
troubles
[2391
§167
Automotive Fuel, Lubricating, and Cooling Systems
Various engine troubles that can be caused by the carburetor are
listed below. Remember that many other conditions outside the
carburetor can also cause these troubles. See the trouble-shooting
chart in Chap. 8 and also the more comprehensive engine troubleshooting chart in the Automotive Engines book for more complete
information on this matter.
1. Excessive fuel consumption can result from a high float level
or a leaky float, sticking or dirty float needle valve, worn jets or
nozzles, stuck metering rod or full-power piston, idle too rich or too
fast, stuck accelerator-pump check valve, or a leaky carburetor.
2. Lack of engine power, acceleration, or high-speed performance can result from a malfunctioning accelerator pump, from the
power step-up on the metering rod not clearing the jet, from dirt
or gum clogging fuel nozzle or jets, from a stuck power piston or
valve, a low float level, dirty air filter, choke stuck or not operating,
air leaks into manifold, antipercolator valve stuck, throttle valve
not fully opening, or a rich mixture due to causes listed in the
previous paragraph.
3. Poor idle can result from an incorrectly adjusted idle mixture
or speed, a clogged idle circuit, or from any of the causes listed in
the previous paragraph.
4. Failure of the engine to start unless primed could be due
to carburetor jets or lines being clogged, a defective choke, a
clogged fuel filter, or air leaks into the manifold.
5. Hard starting with the engine warm could be due to a
defective choke, closed choke valve, or improperly adjusted throttlecracker linkage.
6. Slow engine warm-up could be due to a defectively operating
choke.
7. A smoky, black exhaust is due to a very rich mixture; carburetor conditions that could cause this are listed in item 1, above.
8. If the engine stalls as it warms up, it could be due to a
defective choke or closed choke valve.
9. If the engine stalls after a period of high-speed driving, it
could be due to a malfunctioning antipercolator.
10. If the engine backfires, it could be due to an excessively rich
or lean mixture.
11. If the engine runs but misses, it could be that the proper
amount and ratio of air-fuel mixture is not reaching the engine, and
[240]
Carburetor Service
§168
this might be due to clogged or worn carburetor jets or to an incorrect fuel level in the float bowl.
Several of the conditions noted above can be corrected by carburetor adjustment. Other conditions require removal of the carburetor from the engine so that it can be disassembled, repaired,
and reassembled. The following section describes various adjustments to be made to the carburetor, while later sections describe in
detail how specific carburetors are torn down and rebuilt.
§168. Typical carburetor adjustments Since a great variety of carburetors (estimated at over 500 models) have been used on automotive vehicles in the past 10 years, it is obviously beyond the
scope of this book to provide detailed adjustment and servicing
procedures on all. However, typical adjusting procedures as well
as specific teardown and rebuilding procedures on popular model
carburetors are included. This information will give the reader a
general idea of how these various operations are performed. However, in actual practice in the automotive carburetor shop, the
mechanic should always refer to the carburetor manual for the
specific carburetor he is servicing. This assures proper adjustment
and relationship of all parts on reassembly.
Many years ago, the various gasoline-discharge jets on the carburetor were adjustable, and it was sometimes difficult to balance
them all for proper engine performance. Today, however, jets are
fixed on most applications and, with the exception of the idlemixture jet, require no adjustment. Usually, the only adjustments
to be made on the modern carburetor besides the idle-mixture jet
are establishment of the proper mechanical linkage measurements
between the moving parts in the carburetor. Some carburetors require only a few adjustments, such as the idling-mixture, idlingspeed, float-level, and metering-rod-linkage with the throttle. Others
require, in addition, adjustment of the antipercolator, acceleratorpump linkage, and the slow- and fast-idle speeds. Adjustments discussed below are not necessarily given in proper sequence; since
the sequence varies somewhat from one carburetor to another.
NOTE: Carburetor adjustments should not be made until other
components affecting engine operation are known to be in order.
Engine compression, valve action, ignition system, fuel pump, fuel
strainers, air cleaner, and manifold heat-control valve must all
[2411
§169
Automotive Fuel, Lubricating, and Cooling Systems
be within operating specifications. There must be no air leaks
into the intake manifold, and throttle linkage must be correctly
adjusted. Adjusting the carburetor to compensate for faulty conditions elsewhere will probably further reduce engine performance
and increase fuel consumption.
§169.
The idle-speed and
idle-mixture (Fig. 10-1) are the most commonly made adjustments
on the carburetor and are usually made together. Use of an intakemanifold vacuum gauge (§132) will help in achieving a steady idle
Idle-speed and idle-mixture adjustments
FIG. 10-1. Idle-mixture screw (A)
and idle-speed adjusting screw (B)
on one type of carburetor. (Chevrolet
Motor Division of General Motors
Corporation)
(as indicated by a steady vacuum reading). The throttle adjusting
screw, which controls idling speed, should be adjusted so that the
engine idles at the specified engine rpm (revolutions per minute).
This is approximately one turn of the adjusting screw back from
fully closed throttle. Most car manufacturers give adjusting specifications in terms of engine rpm. To measure engine rpm, a special
rpm indicator, or tachometer, is needed, as explained in §133. The
idle-mixture adjustment is made by turning the idle-mixture
(needle) screw. Correct setting will give smoothest idle. The proper
setting on most carburetors is one to two turns of the idle-mixture
screw back from the fully seated position. To set the idle mixture
accurately, a vacuum gauge (§132) should be used. The vacuum
gauge is attached to the intake manifold, and the idle-mixture screw
is adjusted until the vacuum gauge gives a maximum reading with a
[242]
\,
Carburetor Service
§170
steady needle. After the idle-mixture setting is made, it may be
necessary to readjust the idle speed slightly so as to return the
setting to the speci£ed rpm.
On some applications the carburetor has a fast-idle cam that i~
tied in with the automatic choke. With the engine cold, the choke
valve is closed, and in this position linkage between the choke
valve and fast-idle cam forces the high point on the cam to come
into position under the throttle adjusting screw (Fig. 4-30). This
--c
I"
'2
_1----
-
-_.
FIG. 10-2. Checking the Hoat-Ievel height between Hoat and bowl cover on
one type of carburetor. (Chevrolet Motor Division of General Motors Corporation)
causes a fast idle with the engine cold. When the engine warms up,
the choke valve opens and forces the fast-idle cam to rotate so
that the high point moves out from tmder the adjusting screw. In
this position the engine has a normal slow idle. Adjustment on this
type of carburetor is made by obtaining proper slow idle, as above,
and then adjusting linkage to the choke valve to obtain proper
fast-idle speed.
§170. Float level After considerable service, the lip on the float
level that actuates the needle valve tends to wear, so that the Hoat
level rises, permitting Hooding and an excessively rich mixture. On
the other hand, an excessively low Hoat level will cause a mixture
[2431
§171
Automotive Fuel, Lubricating, and Cooling Systems
that is too lean. On some applications, it is possible to install a
float-level gauge on the carburetor, while on others an inspection
plug may be removed for checking the float-level height without
disassembling the carbmetor. On other applications the float-bowl
cover must be removed and the fuel height or float-level position
measmed. Measurement is usually taken between the fuel or float
and the top of the bowl (Fig. 10-2) or between the bowl cover and
a marking on the float. Adjustment is made by bending the lip
that actuates the needle valve or the arm (or arms) supporting
the float. The float itself should never be bent.
§171 . Accelerator
For various climatic conditions, various
lengths of accelerator-pump-piston travel are desirable. Dming
pump
10-3. Accelerator-pump-Iever
linkage adjustments. Position 1 provides a short stroke for summer operation, position 2 provides an intermediate stroke for average operation,
and position 3 provides a long stroke
for winter operation. (Plymouth Division of Chrysler Corporation)
FIG.
2
3
extremely cold weather, the travel should be the maximum to allow
a larger quantity of gasoline to be discl~arge.
During hot weather,
the travel should be the minimum. Adjustment is provided either
by shifting the linkage rod between the throttle and the accelerator pump into various holes provided in the throttle or the
pump lever (Fig. 10-3), or by bending the linkage to secme a
shorter or a longer stroke.
§172. Metering rod Various sizes of metering rod can be installed
on carburetors using this type of high-speed, full-power circuit
control to secme a leaner or a richer mixtme when this circuit is
operating. The linkage between the throttle and the metering rod
must be correct so that the metering rod will rise to permit the
high-speed, ,full-power circuit to come into action at the correct
throttle op~lkg.
This linkage may be checked by using a gauge
[2441
\
\
,
\
r.arburetor Service
§173
Connector rod
10-4. Checking metering rod and throttle relationship with gauge on one
type of carburetor. (Chevrolet Motor Division of General Motors Corporation)
FIG.
installed in the carburetor in place of the metering rod (Fig. 10-4),
and adjustment is accomplished by bending the throttle connector
rod to secure the proper relationship.
§173. Antipercolator The antipercolator must be adjusted to open
with the throttle in the closed position. This adjustment is made
by opening the throttle some definite amount (for instance, by moving the fast-idle cam around so that the high point is under the
throttle adjusting screw ) and then measuring the clearance between the antipercolator rocker-a.r m level and the operating lever
Clearance
\
10-5. Antipercolator clearance adjustment
point on one type of carburetor.
FIG.
[245J
Automotive Fuel, Lubricating, and Cooling Systems
§174
(Fig. 10-5). Adjustment is made by bending the rocker arm to
secure the proper clearance.
§174. Throttle linkage The throttle linkage on the car must be
adjusted to provide full-throttle opening when the foot pedal is
fully depressed, proper control of hand throttle (where used), and
correct throttle-cracker adjustment for starting. In addition, the
throttle must be fully closed when the foot pedal is in the released
position. The procedures for making these adjustments vary from
car to car, so the manufacturer's specifications should be followed
when adjustments are necessary.
§175.
Carburetor removal To remove a carburetor, first take off
the air cleaner and then disconnect the throttle and choke linkages.
Disconnect hot -air tube to choke (if Fresent). Disconnect the fuel
line and distributor vacuum-advance line from the carburetor, using
two wrenches, as necessary, to avoid damage to the lines or
couplings (see §155). Disconnect wires from switches and other
electric controls (where present). Take off carburetor attaching
nuts or bolts, and lift off carburetor. Try to avoid jarring the carburetor, since it might have accumulations of dirt in the float bowl
and rough treatment might stir this dirt up and cause it to get
into carburetor jets or circuits.
After the carburetor is off, it should be put in a clean place
where dirt or dust cannot get into the fuel inlet or other openings.
§176.
Carburetor overhaul procedures Disassembly and reassembly
procedures on carburetors vary according to their design; the manufacturer's recommendations should be carefully followed. The time
required to overhaul a carburetor varies from approximately % to
1 % hours, according to type. Special carburetor tools are required.
Gauges particularly are needed to gauge clearance, float centering,
float height, choke clearance, and so on.
Special carburetor overhaul kits are supplied for many carburetors. These kits contain all necessary parts (jets, gaskets,
washers, and so forth) required to overhaul the carburetor and
restore it to its original performing condition.
1. General overhaul instructions. Jets or nozzles should never be
cleaned with drills or wires since this would probably enlarge the
cause an excessively rich mixture. Instead, the openopenings a~d
[246]
\
/\
Carburetor Service
§176
ings should be cleaned out with denatured alcohol or similar
recommended solvent. This solvent will remove any gum that is
clogging the opening. Similarly, all circuits or passages in the carburetor body should be washed out with solvent and then blown
out with compressed air. Double-check passages with a Hashlight
to be sure they are cleaned out.
Power pistons that are scored or burred should be replaced; the
piston must slide freely in the bore in the carburetor body. Worn
or scored needle valves or seats must be replaced. Filter screens
must be clean. Accelerator-pump plungers must fit snugly in their
wells. If the leather is damaged, a new plunger must be used.
If the air hom is coated with dirt or carbon, it should be scraped
lightly or sanded with sandpaper and then washed in solvent. Never
use emery cloth, since particles of emery may embed and later
loosen to clog jets or circuits in the carburetor.
Be sure that all residue is washed from the carburetor and that
the carburetor body is clean inside and out.
New carburetor gaskets should be used when the carburetor is
reassembled. The old gaskets are usually damaged when the carburetor is tom down, and there is no use taking a chance on a leak
developing later that would require disassembling the carburetor
again.
2. Cautions. Several important cautions should be observed in
carburetor work.
a. Be sure your hands, the workbench, and tools are really clean.
h. Gasoline, as well as denatured alcohol or other solvent used
to dissolve the gum from carburetor jets and other parts, is
highly flammable. Extreme care must be used in handling
these liquids, particularly some of the solvents, since they will
ignite easily.
c. Handle the air hose with care. Remember, high-pressure air
can drive dirt particles at high speed. If one of these particles
should be blown into the eye, it might damage the eye irreparably. Wear goggles when using the air hose to be safe.
d. Never clean carburetor jets or orifices with wire or drills. This
would probably enlarge the openings and result in excessive
fuel consumption.
e. Always use new gaskets on reassembling the carburetor.
f. The correct carburetor parts must be used on reassembly. Sub[247]
Automotive Fuel, Lubricating, and Cooling Systems
stitute parts that may be somewhat different should not be
installed unless the carburetor manual specifically states that
this may be done. Otherwise, performance and economy may
be lost.
g. Carburetor adjustments should not be made until other components affecting engine operation are in good order. Adjusting the carburetor to compensate for faulty conditions elsewhere will probably result in poorer engine performance and
higher fuel consumption.
h. Do not oil the automatic choke linkage or the automatic
choke.
CHECK YOUR PROGRESS
Progress Quiz 9
Now is your chance to stop and check up on how well you have been
progressing in your reading of Chap. 10. This chapter is an important
one, since every automotive mechanic should be familiar with carburetors
even though he might not specialize in carburetor service work. Since the
carburetor is, after all, an integral part of the engine, a mechanic who
normally works on the engine, the electrical equipment, or other automotive components should understand the part that the carburetor plays
in the operation of the car. The questions below will help you review the
general material on carburetor service that you have just covered.
Completing the Sentences
The sentences below are incomplete. After each sentence there are several words or phrases, only one of which will correctly complete the sentence. Write each sentence down in your notebook, selecting the proper
word or phrase to complete it correctly.
1. Careless cleaning of fuel nozzles so that they are enlarged will result
reduced fuel consumption
lean mixture
excesin
sive fuel consumption
2. Dirt or gum in fuel nozzles or jets may cause
excessive fuel consumption
lack of engine power
smoky, black exhaust
3. A high float level may cause
excessive fuel consumption
a lean mixture
failure to start except when primed
4. A choke valve that is stuck in the closed position may cause
an
overrich mixture cold
an overrich mixture hot
an excessively leaf!, mixture
5. A clog~?
fuel nozzle could result in
excessive fuel consump[248]
\,
Carburetor Service
tion
an overrich mixture
start except when primed
high fioat lev~jnd'u
6. A smoky, black exhaust is probably due to
a very rich mixture
cuit
a very lean mixture
low fioat level
clogged idle cir-
7. The most commonly made adjustments on the carburetor are
idle-mixture and idle-speed
nozzle richness and mixture
fioat level and height
main-
8. During cold-weather operation, it is desirable for the acceleratorpump-piston travel to be
shortened
lengthened
slowed down
§177. Overhauling Chevrolet carburetors A sectional view of a latemodel Chevrolet carburetor is shown in Fig. 10-6. This carburetor
requires only three adjustments; idle-mixture, idle-speed, and floatleve1. In addition, on those models so equipped a throttle-returncheck adjustment is required. Adjustments, disassembly, inspection
of parts, and reassembly of this carburetor are detailed below.
§178. Adjustments (Chevrolet model in Fig. 10-6)
Before making
any carburetor adjustments, the engine should be thoroughly
warmed up. Carburetor-attaching bolts, and manifold-attaching
bolts and must be tight so that no air leaks can occur. The idlemixture and idle-speed adjustments must be made together.
1. Idle-mixture adjustment is made by turning idle-mixture
screw (A in Fig. 10-7) all the way in and then backing off the screw
1 ~ to 2lh turns. Then turn screw either way from this position with
engine idling to obtain smoothest idle.
Caution: When turning screw in, do not turn it in too tightly, or
you will score or scratch the needle valve on the screw.
2. Idle-speed adjustment is made by first making sure hand
throttle and choke buttons are pushed all the way in on the instrument panel. Throttle linkage must be free so that throttle stop
screw (B in Fig. 10-7) is against the stop. Then turn screw in or out
to obtain correct idling speed for the engine. Then recheck idlemixture adjustment to make sure that idle is as smooth as possible.
NOTE: Idle speed varies according to engine model. For example,
specifications call for an idle of 450 to 500 rpm on the model 216
engine and 430 to 450 rpm on the 235 engine. An rpm indicator
(§133) should be used for accurate setting of the idle speed.
[249]
§178
Automotive Fuel, Lubricating, and Cooling Systems
3. Float-level adjustment consists of three parts: adjustment of
the float height, centering of the two floats, and float drop.
a. To adjust float height, remove carburetor air cleaner, disconnect choke wire from choke lever, disconnect fuel line from
carburetor, hold throttle kick lever out of way, and remove
cover assembly by taking out four attaching screws. Lift cover
straight up to avoid damaging floats. With cover gasket still
in position, upend cover assembly on a flat surface and put
special float gauge into position as shown in Fig. 10-8. Tang
in center of gauge should be placed in the main discharge
nozzle. In this position, the floats should just touch the tops of
10-6.- Sectional view of late-model single-barrel carburetor. (Chevrolet
Motor Division of General Motors Corporation)
FIG.
A. Main metering jet
B. Main-well sUPP9rt
C. Air bleeds
D. Idle tube \
E. Idle porh
[250]
\
\
F.
G.
l-I.
I.
/.
Throttle valve
Secondary idle ports
Venturi
Power piston
Power valve
K. Spring
L. Spring-loaded ball
M. Manifold-vacuum
passage
Carburetor Service
§178
the slots in the gauge. If they do not, bend the float arms
vertically until they do.
Do not put pressure on the floats, but do the bending on
the arms themselves.
Caution:
h. To adjust float centering, turn the cover assembly 90 degrees
or onto one side (with gauge vertical) and see whether the
FIG. 10-7. Exterior view of carburetor, showing idle-mixture adjustment
screw (A) and idle-speed adjustment
screw (B). (Chevrolet Motor Division
of General Motors Corporation)
FIG. 10-8. Checking float-height ad-
justment. (Chevrolet Motor Division
of General Motors Corporation)
10-9. Checking centering of
floats. (Chevrolet Motor Division of
General Motors Corporation)
FIG.
[251]
§178
Automotive Fuel, Lubricating, and Cooling Systems
floats rub the sides of the slots in the gauge (Fig. 10-9). Turn
the assembly to one side and then the other to make the check.
If either float rubs, bend the float arm to keep it from rubbing.
Then recheck level adjustment. This adjustment assures that
the floats will not rub the sides of the float bowl.
c. Float drop adjustment is made by turning the cover assembly
right side up so that the floats are suspended freely and then
FIG. 10-10. Checking float drop.
Cover assembly turned right side up.
( Chevrolet Motor Division of General
Motors Corporation)
FIG. 10-11. Checking and adjusting
throttle-return check. (Chevrolet Motor Division of General Motors Corporation)
checking the distance between the bottom of the float and the
gasket surface (Fig. 10-lO ). This distance should be 1 %
inches. If it is not, bend the float tang at the rear of the float
assembly. This adjustment assures sufficient needle-valve opening during high-speed operation for adequate fuel entry.
4. Throttle-return-check adjustment is made with an rpm indicator (§133). Air cleaner must be off the carburetor. With transmission in "Park" position, start engine and run it at fast idle until
it warms up. Make sure engine is running smoothly at idling speed
of 430 to 45<Q, rpm (engine warm) before making throttle-returnAdjust idle speed and mixture if necessary. Then
check adjus~ent.
[252]
\.
Carburetor Service
§179
insert O.OgO-inch feeler gauge between carburetor choke lever cam
and fast-idle lever as shown in Fig. 10-11. Use one wrench on flat
sections of the throttle-return-check shaft to keep it from turning,
and turn the adjusting screw with a second wrench as shown in
Fig. 10-11. Turn adjusting screw until it just touches the throttle
lever contact arm.
§179. Disassembly (Chevrolet model in Fig. 10-6) With carburetor
off the engine, clean off dirt from outside of carburetor. During
the overhaul, be very particular about dirt (see §148 on cleanliness). Refer to Fig. 10-12 and disassemble as follows.
1. Remove four cover screws, and lift off cover. Hold throttle
kick lever out of way, and lift cover straight off to avoid damaging
floats.
2. Upend cover assembly on flat surface, take out float hinge
pin, lift off the float, and remove the float needle. With widetipped screw driver, unscrew float needle seat and remove fiber
gasket. Unscrew main metering jet and power-valve assembly, using
care to avoid losing spring and ball under valve. Take out attaching
screw, and lift straight up on main well support to remove it. Be
careful to avoid damaging the main-well tube.
NOTE: Late-model carburetors used on 235 engines have the
main-well tube pressed into the air horn and extending deep into
the main-well support. On these, the support should not be removed as the air horn, support, and air-horn gasket are serviced as
an assembly in case any part requires replacement.
Complete the disassembly of the cover assembly by taking gasket,
power piston, and spring from cover.
S. Take pump plunger from float bowl by holding plunger all the
way down, removing hairpin retainers from pump link so that link
can be detached from throttle lever and plunger. Plunger can then
be lifted from bowl, and spring and ball check removed from bottom
of the well. Use small screw driver to rotate pump discharge guide
until it can be removed from float bowl. Pump discharge spring
and ball check will then fall out when bowl is turned upside down.
Take off pump-screen retainer and screen.
4. Separate float bowl from throttle body by removing two
attaching screws. Idle-adjusting needle and spring should then
be removed from the throttle body.
[253]
§179
Automotive Fuel, Lubricating, and Cooling Systems
I
(.
I·
-
FIG. 10-12. Disassembled view of one type of single-barrel carburetor. (Chevrolet Motor Division of General Motors Corporation)
1. Cover-attaching
16. Float bowl
33. Pump discharge
screw
17. Throttle-body gasket
spring
2. Air horn
lB. Throttle-body
34. %6 steel pump dis3. Fuel-inlet fitting
assembly
charge ball
4. Air-horn gasket
19. Idle adjusting needle 35. Pump-plunger
5. Float
20. Idle needle spring
assembly
6. Float needle, seat, 21. Throttle-body screw 36. Pump return spring
gasket assembly
22. Choke valve
37. %2 aluminum pump
7. Power spring
23. Choke shaft
check ball
B. Float hinge pin
24. Choke-valve screw 38. Throttle-kicker
9. Power piston
25. Choke-lever screw
screw
10. Main-well support
26. Choke-lever retainer 39. Throttle-kicker
11. Power-valve assem- 27. Choke lever
washer
2B. Bracket screw
40. Throttle kicker
bly
41. Throttle-kicker
12. Main metering jet
29. Bracket nut
13. Attaching screw
30. Choke-shaft spring
spring
14. Pump-screen
31. Choke bracket
42. Throttle-valve screw
retainer
32. Pump discharge
43. Throttle shaft
guide
15. Pump screen
\
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Carburetor Service
§182
5. Inspect all parts. Section 176 covers general overhaul instructions and explains how to clean and inspect carburetor parts. Pay
special heed to the fit of the throttle shaft in the throttle body. If
it is loose, the throttle-body assembly must be replaced since
looseness will throw off throttle valve fit and alignment of the
throttle valve with the idle discharge holes.
§180. Reassembly (Chevrolet model in Fig. 10-6)
Essentially, reassembly is the reverse of disassembly. FolloWing are the special
points to watch.
1. Install idle needle screw and spring in throttle body, tighten
until finger tight, and back off about two turns.
2. Using a new throttle-body gasket, attach body to bowl. Place
clean pump screen in bottom of bowl, and lock retainer in position.
Drop small aluminum ball in pump well, making sure that it will
lift freely from its seat (that is, that it does not stick). Put pump
return spring in pump well, and center it by compressing it with
finger. Install pump plunger, and connect pump link to throttle
lever and pump rod. Attach link with hairpin retainers. Drop large
steel ball into pump discharge cavity, and put bronze spring on
top of ball. Put end of pump discharge guide into bronze spring,
and press guide down until it is flush with bowl surface.
S. Assemble cover by installing float needle seat, using a new
fiber washer. Then put float needle in place. Use a new air-horn
gasket. Put power-piston spring and piston in place, and attach
main-well support to air horn. Install main metering jet and tighten
securely. Hold the power-piston stem down, and install ball, spring,
and plug and tighten securely. Attach float with hinge pin. (Float
tang must face air horn.) Adjust float as already described, and then
install cover assembly on float, attaching it with four screws well
tightened. Hold throttle kick lever out of way when putting
cover into position on bowl.
§ 181. Overhauling Plymouth carburetors Four adjustments are provided on Plymouth carburetors: idle speed, idle mixture, float
height, and accelerator-pump setting. Adjustments, disassembly, inspection, and assembly procedures are detailed below.
§182. Adjustments (Plymouth)
Before making any adjustments,
the engine must be at operating temperature.
[255]
§183
Automotive Fuel, Lubricating, and Cooling Systems
1. Idle speed and idle mixture. First adjust the idle speed to
between 450 and 500 rpm. Then turn idle-mixture screw to give
smoothest operation. A vacuum gauge and a tachometer will help
in making the idle-mixture and idle-speed adjustments (§ 169 ).
2. Float height. Remove air cleaner and air horn from carburetor
so that ftoat is exposed (Fig. 10-13). Use special gauge as shown,
and raise the Boat with finger pressed against the vertical lip until
the needle valve closes. If a gauge is not available, lay straightedge
on ftoat-bowl ftange above the ftoat in place of the gauge. Then
measure down to ftoat , when ftoat is held in raised position as explained above. Distance should be %4 inch (plus or minus 7'64
inch). Adjust by removing ftoat and bending the vertical lip only.
Bend toward ftoat to raise ftoat, away to lower ftoat.
FIG. 10-13. Checking float height.
(Plymouth Division of Chrysler Corporation)
3. Accelerator-pump setting. The procedure of changing the accelerator-pump setting has already been covered in §171 ( see
Fig. 10-3).
§183. Disassembly and reassembly (Plymouth)
With carburetor off
the engine, clean off dirt from outside of carburetor. During overhaul, be very particular about dirt (see §148 on cleanliness). Disassemble as follows.
1. With air horn off, take off hinge pin and Boat. Take out needle '
valve, and feel with the fingernail for any ridges or signs of wear
on the needle. If the needle requires replacement, replace the
needle seat and gasket, too, since the seat and needle valve are
matched at the factory and are serviced together in matched sets.
2. Check #~e
main metering jet and vent tube (Fig. 10-14) after
[256]
\
\
Carburetor Service
§183
cleaning them with solvent and compressed air. Replace as necessary.
3. The power step-up system is shown schematically in Fig.
10-15. Piston can be checked for free operation by pushing it down
about 7{;4 inch and then seeing if it will move up and down freely.
If it sticks or binds, disassemble it, clean the piston and bore, or
FIG.
10-14. The main metering jet
and the vent tube in a carburetor.
(Plymouth Division of Chrysler Corporation)
FIG . 10-15. Power step-up system
showing locations of piston, rod, and
jet. (Plymouth Division of Chrysler
Corporation)
FIG. 10-16. Pump piston, valves, and
pump jet in accelerator system. (Plymouth Division of Chrysler Corporation)
install new parts. With the piston pushed all the way down, there
should be some clearance between the top of the plate and step-up
rod. Bend the step-up rod plate slightly, if necessary, to obtain a
minimum of 0.010-inch clearance.
4. Inspect the idle orifice tube and air-bleed passage to make
sure they are clean. Install a new tube if the old one is damaged.
5. To remove the accelerator-pwnp jet, take out the rivet plug
and unscrew the jet (Fig. 10-16), using a narrow-tipped screw
[257]
§184
Automotive Fuel, Lubricating, and Cooling Systems
driver that will not damage the threads in the body. Clean the jet
with solvent and compressed air. Lift out the accelerator pump,
and examine the leather on the plunger. If it is hard or damaged,
install a new piston. Check the inlet and outlet ball checks for
action, and clean them with solvent and compressed air.
6. Inspect all parts. Section 176 covers general overhaul instructions and explains how to clean and inspect carburetor parts. In
addition, special inspection hints are given in the disassembly instructions above. Pay special heed to the fit of the throttle shaft
in the throttle body. If the fit is loose, calibration and proper action
of the idle- and low-speed circuits will be lost. In such case, the
body and shaft should be replaced.
7. Essentially, reassembly is the reverse of disassembly. As a
rule, disassembly of this carburetor need be carried no further
than is necessary to take care of some defect. However, when a
carburetor is partly torn down, it is little additional trouble to
complete the disassembly so as to check everything in the carburetor. Reassembly then consists of putting the various parts back
into their original places. Since the carburetor is very simple in
design, no difficulty should be experienced in reassembly.
§184. Overhauling
Several manufacturers
make two-barrel, or dual, carburetors. Many automobile manufacturers use this type of carburetor. They are all rather similar in
basic design and operation. However, disassembly and reassembly
procedures do vary from model to model. The typical procedures
described below apply to the carburetor used on recent Buick
automobiles, which is illustrated in Figs. 4-2, 4-8, and 4-11. Be sure
to refer to the manufacturer's service manual before attempting to
disassemble, adjust, and repair other models of two-barrel carburectors.
two-barrel carburetors
§185. Adjustments (two-barrel carburetor) Adjustments that can be
made without disassembling the carburetor include idle-speed, idlemixture, fast-idle, and choke adjustments. Choke adjustment is
covered in §151.
1. Initial idle-mixture and idle-speed adjustments. With engine
stopped, turn both idle needles (or idle-mixture screws, as they are
also called) 'In until they seat lightly. Do not turn in tight since this
will damage valves and seats. Back off each needle exactly one turn.
[258]
\
\
\
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Carburetor Service
§185
Then back off the throttle stop screw, and hold the fast-idle cam in
open-choke position so throttle valves can close fully. Turn throttle
stop screw out until it no longer touches the arm on the throttle
lever. Next, turn it in until it just contacts the arm. Then turn
screw in exactly one complete turn. This gives an engine idle speed
of about 450 rpm.
~
-.:
:.;=~
CHOKE VALVE
HELD CLOSED
CHOKE LEVER
TRIP LEVER
_ ......,,"_"""'-->J" GAUG
FIG. 10-17. Checking fast-idle-cam clearance. (Buick Motor Division of Gen-
eral Motors Corporation)
2. Final idle-mixture and idle-speed adjustments. After the above
initial adjustments are made, start the engine and allow it to idle
until the engine is at operating temperature. Then turn both needle
valves in exactly the same amount until the engine begins to roll,
or run unevenly. Then turn both needle valves out exactly the same
amount until the engine once again begins to roll, or run unevenly.
Finally, turn both needles to a position exactly halfway between
the two extreme positions. The throttle stop screw may require
some readjustment as the needle valves are changed in order to
[259]
§185
Automotive Fuel, Lubdcating, and Cooling Systems
maintain engine idling speed at 450 rpm. These final adjustments
may also be made with the help of a vacuum gauge and a
tachometer (§169).
3. Fast idle. Fast idle is tied in with the choke unloader and
position of the idle adjustment screw. To adjust, first remove the air
cleaner. Then hold choke valve closed and, with cam trip lever in
CHOKE VALVE
FIG. 10-18. Checking choke unloader adjustment. (Buick Motor Division of
General Motors Corporation)
contact with the fast-idle cam, check clearance between the fastidle-cam arm and the boss on the carburetor body. Clearance should
be 0.020 inch (Fig. 10-17). To adjust, loosen lock screw on choke
lever, hold choke valve closed, and tum lever slightly on chokevalve shaft. Tighten lock screw and recheck.
Next, check the choke unloader adjustment (which controls the
amount of choke opening as throttle is opened). Open the throttle
until the stew arm on the throttle-shaft lever hits the boss on the
'Check the clearance between the choke valve and the
body flang~.
[260]
\
\.
§186
Carburetor Service
air hom (Fig. 10-18) with a %6-inch round gauge or No. 12 drill.
To adjust, bend the cam-operating arm on the throttle-shaft lever.
Finally, to set the fast idle, tum the fast-idle adjustment screw
to obtain an engine speed of 1,200 rpm with the engine warm.
§186. Disassembly Be very particular about dirt during carburetor
overhaul. Remember that it takes only a tiny particle of dirt in the
right (or wrong) place to change the operating characteristics of
the carburetor (see §148) .
METERING
ROD ARM
SPRING
METERING ROD
PIN SPRING
iiiii-- -
PUMP ARM
LINK
FIG. 10-19. Removing metering rods and other operating parts. Rod is un
hooked by turning it as shown by white arrow. (Buick Motor Division of General Motors Corporation)
1. With carburetor off engine, remove air hom and disassemble
choke as already explained (§ 152).
2. Take off bowl strainer by removing nut and gasket.
3. D etach throttle connector rod from pump operating lever.
Remove rod by pushing retainer off lower end of rod.
4. Remove dust cover. Turn metering rods so that eyes slip off
pins on piston link (Fig. 10-19) and lift rods out. Do not bend rods.
5. Loosen the screws in the metering-rod arms, pull pin spring
from end of shaft, and pull shaft out, removing arms and link at
same time.
[261]
§186
Automotive Fuel, Lubricating, and Cooling Systems
6. Note location of the code tag and wire clip so they can be
reinstalled in their correct positions; then take off bowl cover. Be
careful not to damage the float.
7. Swing vacuum piston to one side to detach it from link. Then
take link from cover. Take off float assembly by Withdrawing pin,
and take out needle. Remove gasket and two low-speed jets as
necessary.
8. From main body remove vacuum-piston spring, pump-plunger
10-20. Location of jets, housing, and other parts in main body. (Buick
Motor Division of General Motors Corporation)
FIG.
assembly, lower pump spring, screw, jet and hOUSing assembly,
gasket, and pump check (Fig. 10-20).
9. Remove other pal'ts from main body, including rod jets, pumprelief plug and gasket from bowl, and pump intake check ball retainer (Fig. 10-20). Use a wire with a hook on the end of it to
remove retainer. Take oH body flange assembly and gasket.
10. Disassemble vacuum switch by removing hold-down clip
(hold terminal cap in place during this operation). Then remove
cap and switch return spring, and lift out guide block with contact
spring and shims. Do not lose timing shims or the spring washer on
the contact'. spring. Turn body flange over so that plunger and ball
drop out ip, the hand.
[262J
\.
Carburetor Service
§187
11. Remove throttle valves from shaft if necessary to remove
shaft from body flange. Shaft should be tapped out with rawhide
mallet if it sticks. Fast-idle cam and cam trip lever can then be
removed. Idle-mixture screws can then be taken out and, if necessary, idle-port rivet plugs can be removed with special rivet
extractor.
12. Inspect all parts. Section 176 covers general overhaul instructions and explains how to clean and inspect carburetor parts.
In addition, note that the main nozzles are not to be removed from
the main body under any condition. If the main nozzles are damaged, a new body is required. Pay special heed to the fit of the
throttle shaft in its bearings. Excessive clearance will permit air
leaks that will interfere with performance.
§187. Reassembly Always use all new gaskets on reassembly. In
addition, special treatment of certain gaskets is required. Always
soak new needle-seat, bowl-strainer-nut, and pump-relief-plug gaskets in gO-proof denatured alcohol for 15 minutes, then install on
part and let dry before installing the part.
1. To assemble body flange, drive in new idle-port rivet plugs,
and put fast-idle cam and cam trip lever over fast-idle screw so
that tongue on trip lever is held in the notch in cam by hooked end
of cam spring (Fig. 10-21). Install parts on body flange. Slide throttle shaft into body flange with lever at the closed-throttle position.
Put shaft retaining ring over end of shaft with prong points out,
and push ring in against body flange to eliminate shaft end play.
Install throttle valves on shaft with small "c" in circle toward idle
ports. Back off throttle lever adjustment screw, fully close and center throttle valves, and tighten screws. Double-check centering of
valves by holding body flange up to light. Then stake screwheads
and screw shanks lightly. Install springs and idle adjustment screws
in body flange. Assemble vacuum switch into body flange.
2. Install intake check ball and retainer in main body with a
special tool that will assure seating of the retainer in recess at
bottom of pump cylinder. Attach body flange to main body, using
a new gasket. Install, in main body, pump-relief plug and gasket,
metering-rod jets, pump check needle (pointed end down), gasket,
pump jet housing assembly, and attaching screws. Put vacuumpiston spring and lower pump spring in main body, and· install
[263]
§187
Automotive Fuel, Lubricating, and Cooling Systems
pump plunger in cylinder, using care to avoid creasing or curling
edges of plunger leather washer.
3. On cover, install new seat and gasket if old float needle seat
has been removed. Tighten seat firmly but avoid distortion. Attach
float needle to float lever, and install float assembly with pin. Adjust
float and lever assembly with special gauge in place as shown in
Fig. 10-22. With gasket off, bowl cover inverted, and float assembly
resting on seated needle, the Boats should just touch the outer
sides of the gauges and the lower bar of the gauge. Bend arms
shown at X in Fig. 10-22 to adjust.
as
FIG. 10-21. Relationship of fast-idle cam, spring, and trip lever. (Buick Motor
Division of General Motors Corporation)
4. With adjustment complete, remove float assembly and install
both low-speed jets and a new gasket. Then replace float assembly.
Install vacuum-piston link (lip at center opening points out). Attach
piston to link. Carefully place bowl cover on main body, guiding
piston and pump-plunger rod into their proper places in body and
cover.
5. Coat pump operating shaft with light graphite grease, and
start it into bearing in bowl cover. Hold the metering-rod arm so
that it en~gs
the opening in the piston link and the pump arm
so that it" e'Xtends over the pump-plunger rod. Push shaft through
[264]
\
Carburetor Service
§187
one arm and then the other. Install pin spring on end of shaft.
Center pump arm over plunger rod, and tighten lock screw. Install
pump-arm link in plunger rod and inner hole of pump arm, and install pin spring. Ends of links should pOint toward shaft arm. Attach
throttle connector rod first to throttle-shaft lever (with retainer)
and then to pump operating shaft.
6. Adjust accelerating-pump plunger with throttle lever stop
screw backed out and fast-idle cam in the "hot" position so throttle
can be fully closed. Then measure distance from the upper end of
the pump-plunger rod up to the edge of the bowl cover, using a
FIG. 10-22. Check of float-level height
and adjustment of float assembly.
( Buick Motor Division of General
Motors Corporation)
narrow steel scale as shown in Fig. 10-23. The correct distance
should be %6 inch. Adjustment is made by bending throttle connector rod at the upper angle.
7. Insert ends of metering rods in hooked ends of metering-rod
spring, and push rods down to where eyes can rotate over pins on
piston link. Avoid bending rods. Adjust rods, after adjusting accelerator-pump plunger, by backing out throttle level stop screw
so throttle closes completely. Loosen metering-rod-arm clamp
screw (Fig. 10-24), and press down on piston link until metering
rods bottom in carburetor body. While holding rods down and
throttle closed, revolve metering-rod-arm until tongue on arm just
touches lip of piston link. Then tighten metering-rod-arm clamp
screw.
[265J
Automotive Fuel, Lubricating, and Cooling Systems
§1 87
FIG. 10-23. Checking adjustment of accelerator-pump plunger with scale.
(Buick Motor Division of General Motors Corporation)
PISTON
FIG. 10-24. Aajusting metering rods. (Buick Motor Division of General Motors
Corporation)
[266]
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Carburet01' Service
§189
8. Pack dust-cover screw holes in bowl cover with light graphite
grease, and install dust cover. Install bowl strainer and nut with
new gasket. Assemble and install air horn with choke. Adjust carburetor as aheady explained.
§188. Overhauling Ford carburetors Several models of carburetors
have been used in recent years on Ford cars. Adjustments and overhaul procedures on two of these models are outlined below. The
first carburetor discussed was used on all V-8 engines up to and
including the 1951 engine; the second carburetor discussed has been
used on V-8 engines since 1952.
10-25. Partial cutaway view of a carburetor showing accelerator pump
and high-speed circuits. (Ford Motor Company)
FIG.
§189. Adjustments on carburetors shown in Fig. 10-25 Adjustments
required on this carburetor include idle-fuel-mixture, idle-speed,
accelerator-pump-stroke, and Boat-level.
[267]
Automotive Fuel, Lubricating, and Cooling Systems
§189
1. Idle-fu el-mixture adjustment. Turn idle adjustment screws in
until valves seat lightly, then back off one turn. Do not turn in tight
since tlllS will damage valves and seats. Run engine until it reaches
normal operating temperature, and use vacuum gauge (§169) to
adjust screws to give highest and steadiest vacuum reading. Idle
speed may need resetting after fuel-mixture adjustment is made. If
~SCREW
SCREW
-
"
,wnw
-
FIG . 10-26. Disassembled view of carburetor. (Ford Motor Company)
vacuum gauge is not available, screws may be set adjusted as explained in §185, 1 and 2, above.
2. Idle-speed adjustment. Idle speed is adjusted by turning the
idle screw in or out. Specmcations call for an idle speed of 475 to
500 rpm (or 425 rpm on cars with automatic b'ansmission).
3. Accelerating-pump stroke. Accelerating-pump stroke is adjusted by shifting the pump link from one to another of the three
holes in th~
throttle lever (see §171).
[268]
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Carburetor Service
§190
4. Float level. Float level is checked by removing the air horn
and holding it upside down so that a gauge can be placed on the
flange surface of the air horn to measure the distance from this
surface to the bottom of the float (not soldered seam). The distance should be 1.322 to 1.353 inches and is adjusted by bending
the float-lever arm.
FIG.
10-27. Main body of carburetor in disassembled view. (Ford Motor
Company)
§190. Disassembly of carburetor shown in Fig. 10-25 Be very careful about dirt dlll'ing carburetor overhaul. Remember that a tiny
particle of dirt in a nozzle or fuel passage may throw the carburetor
[269]
§190
Automotive Fuel, Lubricating, and Cooling Systems
action off (see §148). Do not remove the throttle plates and shaft
and choke plate and shaft unless they are damaged, as it is hard to
reinstall these parts correctly.
1. Disassembling carburetor (refer to Fig. 10-26) . Remove
choke lever and carburetor throttle kicker by taking off screws and
washers. Disconnect and remove accelerator-pump link. Separate
air horn, main body, and throttle body by removing screws and
washers. Lift accelerator-pump assembly from main body.
FJG. 10-28. Using jet wrench to remove main jets. (Ford Motor Company)
2. Disassembling main body (refer to Fig. 10-27). Remove
screws from nozzle-bar clamps, and take out clamps, pump discharge nozzle, and nozzle bars from main body. Take out the two
drain plugs and gaskets. Then use special jet wrench as shown in
Fig. 10-28, and go through drain holes to take out the two main
jets. Remove power valve and gasket. Bend a wire into a hook, and
extract pump check ball retainer. Turn main body upside down,
and catch ball check and pump discharge needle.
3. Disassembling air horn (refer to Fig. 10-29). Disassemble
air hom by removing the float-lever shaft, float, and needle valve.
Use jet wre~ch
to unscrew needle-valve seat. If necessary, take out
choke-platy screws and remove choke plate and shaft.
[270]
.,
\,
Carburetor Service
§190
4. Disassembling throttle body (refer to Fig. 10-30). The throttle body has only a few parts that can be taken off, including the
idle fuel adjustment needles that can be backed out and the throttle plates and shaft. The plates should not be removed unless they
are damaged and require replacement.
CHOKE PLATE
CHOKE LEVER PLUNGER
FLOAT
FIG. 10-29. Carburetor air horn disassembled. (Ford Motor Company)
5. Inspection of parts. Section 176 covers general overhaul instructions and explainS how to clean and inspect carburetor parts.
Pay special attention to the feed holes in the air hom that discharge
fuel into the air stream to make sure that they are not clogged with
gum or varnish. Jets and valves that are worn should be replaced.
Discard old gaskets, and use new gaskets from the gasket or overhaul kit for the carburetor.
[271]
Automotive Fuel, Lubricating, and Cooling Systems
~19
tHROTTLE SHAFT
AND lEVER
IDLE FUEl ADJUSTMENT
NEEDLES
FIG. 10-30. Throttle body disassembled. (Ford Motor Company )
§191. Reassembly Essentially, reassembly is the reverse of disassembly. To assemble the air horn, install the needle-valve seat and
new gasket. Replace the choke plate and shaft, if they have been
removed. Center the plate, and then tighten attaching screws.
Work the shaft to make sure that the plate is centrally located, and
then stake screws lightly so that they will not loosen. Install float
needle valve and float, and adjust float as already explained. Install
main jets, drain plugs, and gaskets. Install power valve with new
gasket, and place the pump discharge needle, nozzle, and new
gasket in main body. Put four nozzle-bar gaskets in place, place two
nozzle bars in position with air bleeds close to the pump discharge
nozzle, and attach with nozzle-bar clamps. The two long screws
are to be put on the pump discharge side. Install pump check ball
and retainer and accelerator pump.
Mter replacing throttle plates and shaft (if they have been removed) and making sure they are centered in the barrels, tighten
screws and stake them in place. Replace adjustment needles and
springs.
Attach throttle body and air hom to main body with screws and
lock washefs, using new gaskets. Attach choke lever and throttle
kicker
screws and flat washers.
witf
[2721
A
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Carburetor Service
§193
FIG. 10-31. Type of carburetor on which air cleaner is mounted to surround
main body, with main body and throttle body separated. (Ford Motor Company)
§192. Adjustments on carburetor shown in Fig. 10-31
This carburetor was described in detail in §92 and is illustrated in Figs. 5-30
to 5-33. Adjustments are required on idle fuel mixture, idle speed,
accelerator-pump stroke, and fuel level. Adjustments on idle fuel
mixture, idle speed, and accelerator-pump stroke are identical to
those for the carburetor described above (see §189). The fuel-level
check is made by removing the air cleaner and main-body cover
plate and checking the fuel level with a special gauge. The gauge
measures the distance from the flange to the fuel in the float bowl.
Adjustment is made by bending the Hoat-lever tab to raise or lower
the Hoat.
§193. Disassembly of carburetor shown in Fig. 10-31
Be very care-
ful about dirt during carburetor overhaul. Remember that a particle
of dirt can change the carburetor action (§ 148). Do not remove
throttle or choke plates unless it is necessary, since they are hard to
replace properly.
[2731
Automotive Fuel, Lubricating, and Cooling Systems
§193
1. Separate main and throttle bodies by removing the acceleratorpump-link cotter pin and removing link. Then unscrew link pin
from pump shaft, and take out two screws and lock washers holding bodies together.
2. Disassemble main body as follows (refer to Fig. 10-32). Re-
y~
Anchor screw
Main body cover
;.
Caver clomp
Cover to main
body gasket
. /
;;f"'P;'
N~;:
1r:
Retoi!!e71 I. _.;.
washer
SPringtl
Pump rod stud
:"l
~/
Retaining clip
.
Screw (4 reqUired)
(4 required)
Z
(3 reqUid)~.
Link~tJ
r
~Lackwsher
Power valve
diaphragm ~
Screw and
lackwasher
assembly
=';~:.
Air bleed washer.
~/
_;;-
~
~
-i-::;;;:;;::;:g
1i€M
a i n jet
'ir n
~
Power valve
0..
Gasket
Idle
Main
1\((\
tubes~
bod"
O~
.~
Pl ~.
T\
/
S ·
pring
Felt seal
Pump boll check
~
"'"
.
iston
assembly
,
,. . '~
~/
,~
Plug
Gasket
Float needle seal
gasket and clip' ,
assembly
~-Sprmg
Gasket
Boll ~heck
retamer
A-Fuel inlet filter
U
screen
O-Casket
~Fitng
f.'i
FIG. 10-32. Main body disassembled. (Ford Motor Company)
move anchor screw, washer, four main-body-cover attaching screws,
and cover. Take power-valve diaphragm and rod from cover, if
necessary, by removing three screws and retainer. Remove the
main-well tubes, main jets, and idle jet assemblies with special jet
tool (see Figs. 10-33 and 10-34).
3. Disa~mble
throttle body by removing idle-fuel-adjustment
[274]
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.\
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Carburetor Sel'vice
§194
JETS
FIG.
10-33. Using jet wrench to remove main jets. (Ford Motor Company)
FIG.
10-34. Using jet wrench to remove idle jets. (Ford Motol' Company)
needles and springs. If necessary, the throttle plates and shaft may
be removed by filing off tips from screws and removing screws.
Choke plate may be removed in the same manner.
4. Inspect all parts. Parts should be cleaned and inspected as
noted in §176 and §190, 5.
§194. Reassembly of carburetor Essentially, reassembly is the reverse of disassembly. If throttle choke plates have been removed,
[275]
Automotive Fuel, Lubricating, and Cooling Systems
§195
they must be reattached to their shafts and properly centered in
the barrels. Then screws should be tightened and staked lightly in
place. Main body is reassembled by installing idle jet assemblies,
main jets, and main-well tubes. Then the power valve should be
installed with a new gasket. Install float spring, float, and needle
valve, and attach float with hinge pin. Install accelerating-pump
piston, operating rod, and discharge needle. Attach power-diaphragm assembly in cover, making sure that edge of diaphragm can
be seen all the way around under the retainer. This guards against
leakage. Use new gasket and attach cover. Then install main body
on throttle body, using a new gasket. Be sure that the main fuel
tubes enter the small holes in the distribution rings on the choke
shaft. Install retaining screws, accelerator-pump link stud, link,
and cotter pin.
§195. Overhauling
Several manufacturers
supply four-barrel carburetors such as are illustrated in Figs. 5-21
to 5-25. This type of carburetor, also called a quadrijet carburetor,
is used on a number of late-model automobiles. It is particularly
adaptable to the V-8 engine. While the different models and makes
of four-barrel carburetors are similar in operation, they vary in
construction and thus require different adjustment, disassembly,
and reassembly procedures. The typical procedure described below
applies, in general, to the type of Carter carburetors used on Buick,
Cadillac, Oldsmobile, and other automobiles with V-8 engines. Be
sure to refer to the manufacturer's service manual before attempting
to service or adjust other models of four-barrel carburetor.
four-barrel carburetors
§196. Adjustments
(four-barrel unit) Adjustments on this unit are
made on the Roat assemblies, accelerator pump, metering rods,
vapor vent (antipercolator), fast idle, unloader, and lockout. Adjustment procedures follow.
1. Float ad;ustments. Three adjustments are required on the
floats; horizontal, vertical, and drop. Float-bowl cover must be removed before these adjustments can be made. Gasket must
be off. To remove gasket, take out float hinge pins and remove float
assemblies. Then reinstall float assemblies with pins.
a. Horizontal float adjustment is made by turning cover upside
positioning special gauge as shown in Fig. 10-35.
down '~nd
[276]
\
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Carburetor Service
§196
Sides of :Boats should just clear vertical uprights of gauge.
Bend :Boat arms to adjust.
b. Vertical :Boat adjustment is made by bending center parts of
:Boat arms until :Boats just clear horizontal part of gauge (Fig.
10-35).
c. Float drop is adjusted by turning cover upright and measuring
distance :Boats drop from machined face of cover. The specifications and measuring points vary with different carburetors.
On one, distance between free inner ends of :Boats and cover
should be %, inch. On another, distance is measured between
lowest point of :Boat and cover; distance should be 11 %6
inches for primary :Boats and 2 inches for secondary :Boats.
FIG . 10-35. Horizontal and vertical Boat adjustments. (Oldsmobile Division of
General Motors Corporation )
Adjustment is made by removing :Boat assembly and bending
the small tang that contacts the :Boat needle seat. Bend tang
toward seat to reduce drop, away from seat to increase drop.
2. Accelerator-pump adjustment. Back out throttle stop screw
and fast-idle screw until throttle valves are fully seated in their
bores. Remove dust cover and gasket. Place straightedge across
dust-cover boss and note whether upper end of pump arm is parallel
with straightedge. If it is not, bend pump connector rod at the
lower end (where it has a right-angle bend).
3. Metering-rod adjustment. With idle screw backed out so that
throttle valves are fully seated, loosen clamp screw in metering-rod
lever, and then push down on metering-rod link until rods bottom
in carburetor bowl. Now, revolve metering-rod arm until the finger
on the arm contacts the lip on the link, and tighten clamp screw.
[271]
Automotive Fuel, Lubricating, and Cooling Systems
§196
4. Vapor-vent ad;ustment. After pump and metering-rod adjustments are completed, and with throttle lever setscrew backed out so
that throttle valves are seated in bores, note the distance between
the lower edge of the vapor-vent valve and the dust cover (Fig.
10-36). If it is not %2 inch, remove dust cover and bend the vaporvent arm.
5. Fast-idle ad;ustments. Three separate adjustments are required. Carburetor must be completely assembled.
a. Choke-valve adjustment is made by first loosening choke-lever
clamp screw (at the choke-valve shaft) and then holding the
FIG. 10-36. Vapor-vent adjustment.
(Oldsmobile Division of General Motors Corporation)
FIG. 10-37. F ast-idle adjustment.
(Oldsmobile Division of General M 0 tors Corporation)
choke valve closed. Insert a 0.020-inch feeler gauge between
the tang on the fast-idle cam and the boss on the carburetor
casting. Then rotate choke lever toward closed position to
remove all slack from the linkage. Hold lever in this position
and tighten clamp screw.
b. Throttle-valve opening adjustment is made by first backing
out throttle stop screw and then holding choke valve tightly
closed. Then tighten fast-idle adjusting screw against the high
step on the fast-idle cam until there is 0.015 inch opening
betw
~n
the throttle valve and primary bore of the carburetor
on the ide opposite the idle adjusting screws (see Fig. 10-37).
[278]
\
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CarburetOT Service
§196
c. After carburetor is installed, run engine until it and the transmission are warm. Then connect tachometer to measure engine rpm. Put fast-idle screw on step of fast-idle cam. With
air cleaner off, hold choke valve open and adjust fast-idle
screw to obtain 1,600 rpm.
6. Unloader adjustment. The unloader will partly open the choke
valve when the accelerator pedal is pushed to the Hoor; this permits
starting in case the engine has become Hooded during cranking.
FIG. 10-38. Unloader adjustment. (Oldsmobile Division of General Motors
Corporation)
The unloader is checked by holding the throttle lever so that valves
are wide open and then checking the clearance between the upper
edge of the choke valve and the inner wall of the air horn. Clearance should be Ys inch. It is adjusted by bending the tang on the
throttle lever as shown in Fig. 10-38.
[279}
§196
Automotive Fuel, Lubricating, and Cooling Systems
BEND , TANG TO OBTAIN
.010" CLEARANCE
BETWEEN TA.."IG AND
END OF LEVER WHEN
lD!:!J) IN THIS POslTION
FIG. 10-39. Lockout adjustment. (Oldsmobile Division of General Motors Cor-
poration)
7. Lockout adiustment. The lockout prevents the secondary
throttle valves from opening if the choke valve (on primary side)
is still closed. If the secondary throttle valves opened when the
engine was cold and the choke valve closed, the engine would
probably stall from the excessively lean mixture. And during cranking, opening of the secondary throttle valves would prevent the
choking action so necessary for starting. The fast-idle and other
adjustments described above should be made before the lockout
adjustment. To make the adjustment, hold choke valve tightly
closed and open primary throttle valves all the way. Note if tang
on secondary throttle arm engages in notch on lockout lever to
prevent secondary throttle shaft movement. Then hold choke valve
wide open, and open primary throttle valves all the way. Lockout
lever should now fall free to allow secondary throttle valves to
open before the primary throttle valves are fully opened. If these
two actions\ do not occur, adjust by bending tang on the secondary
throttle l ~er
to attain proper clearance (Figs. 10-39 and 10-40).
[28OJ
\
Cm'buretor Se1'vice
§197
FIG. 10-40. Lockout tang and lever-clearance adjustment. (Oldsmobile Divi-
sion of General Motors Corporation)
§197. Disassembly Be very careful about dirt during any carburetor overhaul work. It takes only a tiny particle or two of dirt to
change the operating characteristics of the carburetor and possibly
result in poor engine performance (see §148). Disassembly procedure can be divided into sections: according to the part of the
carburetor being disassembled.
1. Disassembly of air horn (bowl cover) (see Fig. 10-41)
a. Remove the following parts: gasoline inlet fitting, screen, and
gasket assembly; throttle connector rod; choke connector rod;
dust cover and gasket; choke lever (from choke shaft); choke
valve (after filing off staked ends of the two attaching
screws); choke housing, gasket, and baffle plate (after taking
out three screws and retainers). Then proceed as follows.
h. Rotate choke shaft to lift piston from housing and remove
shaft.
c. Remove piston housing by taking out three screws.
d. Remove pin spring from accelerator-pump connector link.
[281]
Automotive Fuel, Lubricating, and Cooling Systems
§.1 97
t-..-
Screws
SCr.w-.........
lockwoshe,.
___...;w
<"Retoiner
., ~":'
u {;,
BoUI.
K
r
P;n
/0",.
Choke Piston
Screw
Choke
pump,
FIG. 10-41. Disassembled view of bowl cover. (Cadillac Motor Car Division
of General Motors Corporation)
.e. Slide upper end of pump connector link from pump arm (see
Fig. 10-42), and rotate link around lever so link can be re-
f.
moved.
Loosen screw holding pump arm to shaft. Remove atrriospheric
vent arm (vapor-vent arm) by taking out screw. Loosen
metering-rod-arm screw. (See Fig. 10-42 for location of these
scr~w.
)
t\
'.
[282]
\
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Carburetor Service
§197
P UMP CONNECTOR LINK
10-42. Various parts located in the metering-rod housing. (Oldsmobile
Division of Geneml Motors Corporation)
FIG.
10-43. Location of screws attaching the air horn. (Oldsmobile Division
of General Motors Corporation)
FIG.
[283]
Automotive Fuel, Lubricating, and Cooling Systems
§197
g. Unwind throttle return spring (a piece of tag wire is handy
for this).
h. Slide pump countershaft and lever assembly from carburetor.
Pump arm, metering-rod arm, and the metering rods can then
be luted out.
i. Remove the 16 short, medium, and long screws attaching the
cover (or air hom) to the carburetor body or bowl assembly
(see Fig. 10-43).
j. Lift cover assembly off bowl assembly.
2. Disassembly of carbureto1' body (bowl assembly)
a. Remove pump guide, spring and plunger assembly, and the
vacuometer spring.
b. Use special tool to remove pump inlet ball retainer from the
bottom of the pump cylinder.
c. Remove pump discharge nozzle housing and gasket by taking
FIG. 10-44. Removing screws attaching the air horn. (Oldsmobile Division of
Corporation)
General Mo~rs
\
[284]
'\
\.
Carburetor Service
§197
out screw. Turn carburetor over and remove small pump discharge needle (brass).
d. Remove passage screw plug.
e. Remove primary and secondary metering -rod jets (two each ).
Do not mix these, as they are of different sizes!
f. Remove two low-speed jets.
g. Loosen four screws attaching throttle body to carburetor bowl
(Fig. 10-44), and separate body from bowl. Remove gasket.
S. Disassembly of air hom (01' cover). Remove two float assemblies by taking out the hinge pins. Remove needles and needle
seats. Mark or group parts so that the primary and secondary parts
are not mixed.
Caution: Do not mix the needles and seats!
Take off vacuum piston and link, and remove gasket from air
horn.
4. Disassembly of throttle body. Remove idle adjusting screws
(on primary side only on many models), idle-port rivet plugs,
fast-idle-cam screw and cam assembly, and the connector rod linking primary and secondary throttle shafts (by taking off springs
CONNECTOR ROD
PRIMARY THROTTLE
LEVER ASSEMBLY
FIG. 10-45. Throttle-body-Iever details. (Oldsmobile Division of General Motors Corporation)
[285]
§198
Automotive Fuel, Lubricating, and Cooling System,s
and washers), See Fig. 10-45. Then remove other parts from throttle shafts (springs, screws, and levers). Note their relationship carefully, so that you will be able to replace them in same position.
5. Inspection of parts. Refer to §176 for details of overhaul and
parts-inspection procedures.
10-46. Installing primary throttle levers. (Oldsmobile Division of General
111 otors C orpomtion)
FIG.
§198. Carburetor reassembly 1. Assembling throttle body. Install
new idle-port plugs. Put springs on idle adjusting screws and turn
screws in finger-tight. Back off one turn. Do not tighten more than
finger-tight, or you will damage screw tips or seats. Install secondary throttle-return spring and lever. Wind spring one-half turn
with tag wire. Continue as follows.
a. Install primary shaft thrust washer and inner throttle-shaft
arm and dog. Hook spring on outer throttle lever and shaft
dog, and install outer lever (see Fig. 10-46 ).
h. Use Hat washers on each side of levers, and install connector
rod. \
c. Ope
[286]
throttle valves, and install fast-idle-cam assembly as
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Carburetor Service
§198
shown in Fig. 10-47. Make sure tang on choke lever is inserted
under spring on fast-idle cam.
d. Put new gasket on carburetor bowl, and attach throttle body
to bowl with four screws and lock washers. Make sure gasket
lines up with vacuum passage.
BE CERTAIN LEVERS
ARE POSITIONED CORltECTLY
10-47. Installing fast-idle-cam assembly. (Oldsmobile Division of General
Motors Corporation)
FIG.
2. Assembling carburetor body
a. Install primary and secondary metering-rod jets. The primary
jets have the large holes. Do not mix primary and secondary
jetsl
b. Install two low-speed jets (primary side).
c. Install steel pump inlet ball check and retainer, pump passage
screw plug, brass pump discharge check needle (point down) ,
pump discharge nozzle gasket, nozzle assembly, and attaching
screw. Install vacuometer spring.
3. Assembling air horn
a. Install primary and secondary float needle seats. Do not mix
these! Needles and seats are factory-matched and must not
be interchanged.
[287]
§198
Automotive Fuel, Lubricating, and Cooling Systems
b. Temporarily install float assemblies with needles, but do not
put gasket on. Check float horizontal and vertical adjustments and drop, as already explained. Then take off float
assemblies, and install gasket.
c. Attach pump-arm link in outer hole of pump-arm and screw
assembly, and install spring to retain it.
d. Install spring and guide over pump-plunger shaft. Insert shaft
through air horn, and fasten with pump-arm link.
e. Install vacuometer link and piston with lip on link toward air
horn.
f. Reinstall primary and secondary float assemblies with needles
attached.
g. Place air-horn assembly on carburetor body, making sure that
the vacuometer piston and the pump plunger enter their
proper bores. Attach with 16 screws (see Fig. 10-43). Tighten
evenly and in sequence.
h. Install metering rods. Catch rod spring loop with lower end of
rod as rod is inserted and twist eye of rod onto piston-link
assembly.
i. Install throttle return spring on pump countershaft; then install shaft by sliding it through pump operating arm and
metering-rod arm. Make sure metering-rod operating arm is
in slot in the vacuometer piston link. Tighten pump-arm
screw.
i. Place washer on lower end of throttle connector rod, install
rod in throttle lever, and pump countershaft lever. Attach
with spring and clip at bottom and with pin spring at top.
Wind throttle return spring one turn.
k. Install atmospheric vent arm.
l. Install new vacuum-passage seal in choke housing, and attach
housing.
m. Install choke shaft with piston, guiding piston into cylinder in
housing and then rotating shaft so that piston enters.
n. Put choke valve on shaft (C on top), center it, and install
screws.
o. Put bafHe plate in choke housing, and install choke cover with
thermostatic spring. Set at index and retain with three screws
and clips.
[288]
'.
Carburetor Service
§199
p. Install choke operating lever on shaft, and tighten screw just
enough to hold it. Install choke connector rod in choke
operating lever; retain lower end of rod with pin spring.
q. Make adjustments as already described (§ 196).
§199. Carburetor installation Examine the carburetor gasket, and
make sure it is in perfect condition. Replace it if you have any
doubt as to its condition. Put carburetor into position on intake
manifold, and attach with nuts or bolts. Connect fuel line and
distributor vacuum-advance line to carburetor, using two wrenches
as necessary to avoid damage to the lines or couplings (§ 155).
Connect wires to switches and other electric controls ( where
present). Make idle-speed, idle-mixture, and other adjustments as
already explained. Install air cleaner.
CHAPTER CHECKUP
NOTE: Since the following is a chapter review test, you should review
the chapter before taking the test.
You have just completed a chapter on one speCialized automotive service, carburetor overhaul and repair. It may be that you will not have a
great deal to do with carburetors when you work in the service shop.
Nevertheless, it will help you in your other work to know how typical
carburetors are constructed, how they operate, and what services they require. The following checkup will help you test yourself on how well
you remember the material you have just covered on carburetor overhaul.
If you are not sure of an answer, reread the pages that will clarify it for
you.
Unscrambling Carburetor Trouble Causes
There are two lists below. One is headed Trouble and the other is
headed Cause. Note that the causes are more numerous than the troubles. There usually can be several causes of any particular trouble. To unscramble the lists, take each item in the Trouble list, and write it down
in your notebook. Then write after it the items you select from the
Cause list that could cause the trouble. After each trouble, a number is
given: this is the number of items you should select from the Cause list
that could cause the trouble. Note that a cause may appear more than
once since a cause can lead to more than one trouble. The lists below are
not intended to be all-inclusive; they are merely some of the more common troubles and trouble causes.
[289]
Automotive Fuel, Lubricating, and Cooling Systems
Trouble
excessive fuel consumption (4)
lack of power (4)
failure to start unless primed (3)
hard starting (engine warm) (2)
Cause
throttle cracker misadjusted
defective choke
clogged jets or nozzles
choke valve closed
high float level
worn jet or nozzles
stuck check valve
low float level
clogged jets or nozzles
stuck metering rod or power piston
dirty air filter
air leaks into manifold
clogged fuel filter
Service Procedures
In the following, you are asked to write down carburetor troubles,
service cautions, or overhaul procedures. Write them in your notebook.
1. Make a list of troubles that could result from causes in the carburetor.
2. Make a list of typical carburetor adjustments and describe briefly
how to make these adjustments.
3. Describe a typical carburetor-removal procedure.
4. List the main steps in carburetor overhaul.
5. List the cautions to be observed in carburetor repair work.
6. Prepare detailed disassembly, inspection, reassembly, and adjustment procedures on one or more carburetors. If possible, prepare
these by using actual carburetors along with the carburetor manuals
that apply to them. The best way to do this is to follow the procedure
in the manual, step by step, and write down each step as you do it.
You will probably wish to write the procedure down on separate
sheets of paper first and then copy it into your notebook. This will
keep your notebook clean.
SUGGESTIONS FOR FURTHER STUDY
Examine various carburetors and carburetor manuals in the shop. If
possible, observe a carburetor specialist at work overhauling carburetors.
Note how he does each step, the special tools he uses, the manuals he
refers to for speCifications, part numbers of new parts or repair kits he
needs, and the adjustments he makes. Handle and overhaul carburetors
if you can. Study all the carburetor manuals you can find, and note the
construction Of the different types of carburetors and the procedures
used to overhaul and adjust them.
[290]
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11: Engine lubl'icating systems
THIS CHAPTER discusses friction as it is related to engine operation and describes the various types of friction. It discusses the different types of lubricating systems used in engines to reduce friction
and the different kinds of bearings used between moving surfaces
in the engine.
§200. Friction Friction is the resistance to motion between two
bodies in contact with each other. If you put this book on a table,
you would find that it takes a certain amount of force to push it
across the table top. This force overcomes the friction. If you put a
second book on top of the first book, you would find that you would
have to push harder to move the two books. The more weight you
added, the harder you would have to push. Thus friction, or resistance to motion, increases with the load. In the engine the load
between moving surfaces (in the bearings) may be well above 1,000
psi (pounds per square inch). This means that friction could be
quite high. However, the lubricating oil keeps the friction at a
relatively low value, as explained in following sections. Actually,
friction can be divided into three classes; dry, greasy, and viscous.
§201. Dry friction Dry friction is the friction, or resistance to
relative motion, between two solids. If a rough board is dragged
across a rough floor, a certain pull is required. The amount of pull
depends on the roughness of the surfaces and the weight of the
board. For example, suppose you found that it took a pull of 10
pounds to drag a rough board across a rough floor. If you smoothed
off the floor and board with sandpaper, you might find that it would
then take only 5 pounds to drag the board across the floor. This
gives you a clue to what dry friction is. It is considered to be caused
by surface irregularities that catch against each other. Even objects
machined to extreme smoothness have slight microscopic irregularities that cause resistance to relative motion, or friction. Thus even
smooth, hard-metal surfaces that have relative motion under load
[291]
§202
Automotive Fuel, Lubricating, and Cooling Systems
with dry friction would soon wear. The tiny irregularities would
catch on each other and tear off metal particles. These particles
would then gouge out pits and scratches in the moving surfaces.
Soon, the metal surfaces would be very rough and bigger particles
would be broken off. The friction and wear would go up rapidly. In
addition, considerable amounts of heat would be produced by the
rubbing and gouging action. In fact, enough heat might result to
cause the metal to melt in spots. When this happens, the two moving
surfaces would momentarily weld in the melted spots; that is, there
would be an actual joining of the two metal surfaces by small
welded spots. With further relative movement, these welds would
break, making the surfaces still rougher.
This sort of thing actually happens in machines. For example,
under certain conditions, the piston rings in an engine cylinder
weld (in small spots, of course) to the cylinder walls. These welds
break as the rings continue to move, leaving gouged-out spots in the
rings and walls.
§202. Greasy friction Greasy friction is the friction between two
solids that have been coated with a very thin film of oil (and thus
have what is called borderline lubrication). The nature of greasy
friction is not very well understood. It is assumed that the film of
oil fills the surface irregularities of the solids so that the two moving
surfaces are almost perfectly smooth. When greasy friction exists,
the resistance to motion between surfaces is much less than with
dry friction. In automotive engines, greasy friction may exist in
bearings and between piston rings and cylinder walls when the
engine is first started. At this time, most of the lubricating oil may
have drained from the surfaces so that only a thin film remains.
After the engine has been started and the lubrication system has
gone to work, the surfaces will be supplied with more oil. But before
this happens, the surfaces have only greasy friction. With greasy
friction, resistance to motion is less than with dry friction, but wear
will still take place at a relatively fast rate (when compared with
wear during full lubrication ).
§203. Viscous friction "Viscosity" is a term that refers to the tendency of liquids, such as oil, to resist Howing. A heavy oil is more
viscous thaQ a light oil; it Hows more slowly. Water has a relatively
low viscollity; it Hows easily. Viscous friction is the friction, or
[292]
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Engine Lubricating Systems
§204
resistance to relative motion, between adjacent layers of liquid. As
applied to machines, viscous friction occurs during relative motion
between two lubricated surfaces (Fig. 11-1). Figure 11-1 shows,
in greatly exaggerated view, an object W moving over a stationary
object, the two being separated by lubricating oil. The oil is shown
in five layers, A to E, for simplicity. (Actually, we are simplifying
the entire explanation so that the theory of viscous friction can be
understood more easily.)
In the illustration, layer A adheres to the moving object (W) and
moves at the same speed as W, as indicated by the arrow. A layer
of oil (E) adheres to the stationary object and is therefore stationary. Thus, there must be relative motion between the layers of
w
~
A
8
__
•
c0
E
Stationory
FIG. 11-1. Viscous friction is the friction between layers of liquid moVing at
different speeds or, in the illustration, between layers A, B, C, D, and E.
oil A and E. This is visualized as a slippage, or relative movement,
between many layers of oil that are between layers A and E. The
nearer a layer is to the stationary layer, the less it moves. This is
shown by the shorter and shorter arrows in layers B, C, and D.
Essentially, then, the friction is between a great number of oil
layers. There must be slippage between the layers, and it requires
force to make the slippage occur.
§204. Theory of lubrication We have already mentioned some of
the things that happen during lubrication. The two objects in
relative motion are held apart by a film, or layers, of oil. Thus, there
is friction only between moving layers of oil, rather than between
the actual objects. The friction between the oil layers, or viscous
friction, is much smaller that that between solid objects (dry friction). Figure 11-1 shows how the layers act between two flat surfaces. Figure 11-2 shows how they might a.ct between a rotating
shaft journal and a stationary bearing. Layers of oil cling to the
[293]
Automotive Fuel, Lubricating, and Cooling Systems
§205
rotating journal and are carried around with it. These oil layers
act somewhat like wedges and wedge in between the shaft journal
and the stationary bearing. The wedging action actually lifts the
journal off the bearing, so that the shaft weight is supported by the
oil layers.
Figure 11-3 shows how the area of maximum loading, or highpressure area between shaft and bearing, shifts around with changing
shaft sp eed. When the sh aft is at rest, the load is straight down,
FIG. 11-2. Shaft rotation causes layers of clinging
oil to be dragged around with it, so that oil moves
from the wide space A to the narrow space B, and
thus supports the shaft weight W on an oil film.
LUBRICANT ENTRANCE
~
HIGH PRESSURE AREA
HIGH PRESSURE AREA
HIGH PRESSURE AREA
SHAFT AT FULL SPEED
FIG. 11-3. The high-pressure area, or area of maximum loading, varies with
shaft speed. Clearance between shaft and journal exaggerated.
SHAFT AT REST
SHAFT STARTING TO ROTATE
and the lubricating oil is squeezed out from between the shaft and
bearing. When the shaft starts to rotate, the oil layers wedge between the shaft and bearing, lifting the shaft off the bearing. In
effect, the shaft tries to "climb" the right-hand side of the bearing
because of the frictional effect between the oil layers. However, as
shaft speed increases, the wedging action also increases, thereby
transferring the area of maximum pressure toward the left as shown
in the right-hand illustmtion.
§205. Types \ of bearings Generally speaking, the word "bearing"
means any hing that supports a load. So far as machines are con[294]
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Engine Lubricating Systems
§206
cerned, it means anything that supports or confines an object in
sliding, rotating, or oscillating motion. Machine bearings are classified as either friction-type or antifriction-type bearings. These two
names are somewhat misleading, since they would indicate that one
type of bearing has friction while the other does not. Actually, the
friction-type bearing does have a greater amount of friction, other
factors being equal. But both provide low friction between moving
parts. Figure 11-4 shows graphically the differences between fricANTI FRICTION
FRICTION
FIG. 11-4. Graphic representation of friction and antifriction bearings.
tion and antifriction bearings. In the friction bearing, one body
slides over another; the load is supported on layers of oil as shown
in Fig. 11-1. In the antifriction bearing, the surfaces are separated
by balls or rollers so that there is rolling friction between the two
surfaces and the balls or rollers.
§206. Friction bearings Friction bearings have sliding contact between the moving surfaces, as already noted. The load is actually
Three types of friction-bearing surfaces in engine.
[295]
Automotive Fuel, Lubricating, and Cooling Systems
§206
supported by layers of oil. In the automotive engine, there are three
types of bearing surfaces that can be called friction bearings. These
are illustrated in Fig. 11-5 and can be called ioumal, guide, and
thrust. The journal-type friction bearing can be symbolized by two
FIG. 11-6. Various bearings
Bronze Company)
1. Rocker-arm bushing
2. Valve-guide bushing
3. Distributor bushing
-upper
4. Distributor bushing
-lower
5. Piston-pin bushing
6. Camshaft bushing
7. Connecting-rod
bearing
8. Clutch pilot bushing
9. Flanged main
bearing
and bushings used in a typical engine. (Johnson
10. Starter bushingdrive end
11. Starter bushingcommutator end
12. Oil-pump bushing
13. Distributor thrust
plate
14. Intermediate main
bearing
15. Generator bushing
16. Connecting-rod
bearing-floating
type
17. Front main bearing
18. Camshaft thrust
plate
19. Camshaft bushing
20. Fan thrust plate
21. Water-pump bushing-front
22. Water-pump bushing-rear
23. Piston-pin bushing
hands holding a turning shaft, as shown to the upper left in the
illustration. The hands support the turning shaft in the same way
that the b6{lring supports a shaft journal in an engine. There are
numerous\ bearings of this type in the engine (Fig. 11-6). The
[296]
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Engine Lubricating Systems
§207
crankshaft (or main) bearings, connecting-rod bearings, camshaft
bearings, and piston-pin bearings are but a few. Some of these
bearings are split into an upper half and a lower half. Others are
of the bushing, or one-piece, type.
The bearing surface between the cylinder wall and the piston
and piston rings is of the guide type. That is, the cylinder wall
guides the piston up and down in its path. Of course, the piston
rings also seal in compression and combustion pressure and control
the oil as explained on a later page.
There is one main bearing in the engine that has thrust faces
Annular
groove
Lining thickness
Distributing
groove
Porting line cnomfer
11-7. Typical bearing half with parts named. Note oil grooves. (FederalMogul Corporation)
FIG.
(right in Fig. 11-5). The thrust faces hold the shaft in position so
that it does not shift endwise as it rotates. They therefore take the
endwise thrust of the shaft as it attempts to move back and forth in
the engine.
Another book in the McGraw-Hill Automotive Mechanics Series
(Automotive Engines) covers engine bearings in detail.
§207. Friction-bearing lubrication In the automotive engine the
friction bearings and the lubricating system are so designed as to
permit a constant flow of lubricating oil across the bearing surfaces.
Oil enters the clearance space between the bearing and journal,
passes across the bearing face, and drains back into the oil reservoir
(or crankcase) at the bottom of the engine. Many bearings have on
grooves which help spread the oil across the face of the bearing.
They also serve as oil reservoirs to hold some oil for initial lubrication just after the engine is started. Figure 11-7 shows a typical
[297]
Automotive Fuel, Lubricating, and Cooling Systems
§208
bearing half with the various parts named. Note the annular and
distributing grooves which are cut in the bearing face. Oil enters
from the oil hole and moves around in the annular groove to the
distributing grooves. Here, it is picked up by the rotating shaft
journal and is carried around so that oil is distributed around the
entire face of the bearing.
§208. Antifriction bearings Figure 11-8 shows three types of antifrktion bearings; ball, roller, and tapered roller. The ball bearing
has an inner and an outer race in which symmetrical grooves have
been cut. Balls roll in these two race grooves. The balls are held
Outer race
Spacer
Inner
race
BALL BEARING
ROLLER BEARING
TAPERED
ROLLER BEARING
FIG, 11-8. Antifriction bearings.
apart by a spacer assembly. When one of the races is held stationary
and the other rotates, the balls roll in the two races to permit lowfriction rotation.
The roller bearing is similar to the ball bearing except that it has
rollers (plain or tapered). The rollers roll between the inner and
outer races. In the ball bearing, there is spot contact between the
balls and the races. In the roUer bearing, there is line contact between the rollers and races.
Antifriction bearings are usually lubricated by grease. Essentially,
grease is oil mixed with a solidifying agent (§216). The solidifying
agent does not directly lubricate the balls or rollers, but it does
hold the ~il
in the bearing so that the bearing gets proper
lubricatiol,l.
[298J
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Engine Lubricating Systems
§209
§209. Purpose of engine lubricating system We normally think of
lubricating oil as a substance that makes possible minimum wear or
low frictional loss between adjacent moving surfaces. However, the
lubricating oil circulating through the engine to all moving parts
requiring lubrication performs other jobs. The lubricating oil must
1. Lubricate moving parts to minimize wear.
2. Lubricate moving parts to minimize power loss from friction.
S. Remove heat from engine parts by acting as a cooling agent.
4. Absorb shocks between bearings and other engine parts, thus
reducing engine noise and extending engine life.
5. Form a good seal between piston rings and cylinder walls.
6. Act as a cleaning agent.
1 and 2. Minimizing wear and power loss from friction. Friction
has been discussed in some detail (§ §200 to 203). The type of
friction encountered in the engine is normally viscous friction, that
is, the friction between adjacent moving layers of oil. If the lubricating system does not function properly, sufficient oil will not be
supplied to moving parts, and greasy or even dry friction will result between moving surfaces. This would cause, at the least, considerable power loss, since power would be used in overcoming
these types of friction. At the worst, major damage would occur to
engine parts as greasy or dry friction developed. Bearings would
wear with extreme rapidity; the heat resulting from dry or greasy
friction would cause bearing disintegration and failure, so that connecting rods and other parts would be broken. Insufficient lubrication of cylinder walls would cause rapid wear and scoring of
walls, rings, and pistons. A properly operating engine lubricating
system supplies all moving parts with sufficient oil so that only
viscous friction is obtained.
3. Removing heat from engine parts. The engine oil is in rapid
circulation throughout the engine lubrication system. All bearings
and moving parts are bathed in constant streams of oil. In addition
to providing lubrication, the oil absorbs heat from engine parts and
carries it back into the oil pan. The oil pan in turn absorbs heat
from the oil, transferring it to the surrounding air. The oil thus acts
as a cooling agent.
4. Absorbing shocks between bearings and other engine parts. As
the piston approaches the end of the compression stroke and the
[299J
Automotive Fuel, Lubricating, and Cooling Systems
§210
mixture in the cylinder is ignited, pressure in the cylinder suddenly
increases many times. A load of as much as 2% tons is suddenly
imposed on the top of a 3-inch piston as combustion takes place.
This sudden increase in pressure causes the piston to thrust down
hard through the piston-pin bearing, connecting rod, and connecting-rod bearing. There is always some space or clearance between bearings and journals; this space is filled with oil. When the
load suddenly increases as described above, the layers of oil between bearings and journals must act as cushions, resisting penetration or "squeezing out," and must continue to interpose a film of
oil between the adjacent metal surfaces. In thus absorbing and
cushioning the hammerlike effect of the suddenly imposed loads,
the oil quiets the engine and reduces wear of parts.
5. Forming a seal between piston rings and cylinder walls. Piston
rings must form a gastight seal with the cylinder walls, and the lubricating oil that is delivered to the cylinder walls helps the piston
rings to accomplish this. The oil film on the cylinder walls compensates for microscopic irregularities in the fit between the rings
and walls and fills in any gaps through which gas might escape.
The oil film also provides lubrication of the rings, so that they can
move easily in the piston-ring grooves and on the cylinder walls.
6. Acting as a cleaning agent. The oil, as it circulates through the
engine, tends to wash off and carry away dirt, particles of carbon,
and other foreign matter. As the oil picks up this material, it carries
it back to the crankcase. There, larger particles drop to the bottom
of the oil pan. Many of the smaller particles are removed from the
oil by oil-filter action.
§210. Source of oil Engine oil, as well as gasoline and various
automobile lubricants, comes from petroleum, or crude oil. As mentioned in §l02, petroleum is found in reservoirs, pools, under the·
ground. Evidence indicates it was formed from animal or plant
sources millions of years ago. The oil is "recovered," or removed
from the earth, by wells drilled down to the reservoirs.
The petroleum, as it comes from the ground, is not usable for
lubricating purposes. It must first be refined. This refining process
separates the petroleum into various parts, or constituents. A simplified explaQ.ation of the refining process might run like this. The
petroleum is heated in an enclosed chamber, or still. As the petro[300]
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Engine Lubricating Systems
§211
leum temperature increases, the more volatile parts evaporate first
(see §l03). These vapors are led from the enclosed chamber
through tubing to cooler chambers where they condense. These
more volatile parts of the petroleum form gasoline. As the petroleum is heated to higher and higher temperatures, the less and less
volatile parts form engine oil and various heavier products, including tar. Properties of gasoline are described in Chap. 7. Properties of engine oils are discussed in §211. Properties of various other
automotive lubricants are considered in §216.
NOTE: LPG, or liquefied petroleum gas, is also obtained from
petroleum, and it is the most volatile fraction (or part) of the petroleum, tending to turn to vapor even at atmospheric pressure.
§211. Properties of oil A satisfactory engine lubricating oil must
have certain characteristics. It must have proper (1) body and
fluidity, or viscosity; (2) resistance to carbon formation; and (3)
resistance to oxidation.
1. Viscosity (body and fluidity). Primarily, viscosity is the most
important characteristic of lubricating oil. Viscosity refers to the
tendency of oil to resist flowing. In a bearing and journal, layers of
oil adhere to the bearing and journal surfaces. These layers must
move or slip with respect to each other, and the viscosity of the oil
determines the ease with which this slipping can take place. Viscosity changes with temperature, since increasing temperature
causes oil to thin and have a lower viscosity, while decreaSing temperature causes oil to thicken and have a higher viscosity. Viscosity
may be divided for discussion into two parts, body and fluidity.
Body has to do with the resistance to oil-film puncture, or penetration, during the application of heavy loads. When the power stroke
begins, for example, bearing loads sharply increase. Oil body prevents the load from squeezing out the film of oil between the
journal and the bearing. This property cushions shock loads, helps
maintain a good seal between piston rings and cylinder walls, and
maintains an adequate oil film on all bearing surfaces under load.
Fluidity has to do with the ease with which the oil flows through
oil lines and spreads over bearing surfaces. In some respects, fluidity
and body are opposing characteristics, since the more fluid an oil
is, the less body it has. The oil used in any particular engine must
have sufficient body to perform as explained in the previous para[3011
§211
Automotive Fuel, Lubricating, and Cooling Systems
graph and yet must have sufficient fluidity to flow freely through
all oil lines and spread effectively over all bearing surfaces. Late
types of engines have more closely fitted bearings with smaller clearances and consequently require oils of greater fluidity that will flow
readily into the spaces between bearings and journals. Such engines
use oils of lower viscosity.
Temperature influences viscosity. Increasing temperature causes
oil to lose body and gain fluidity, while decreasing temperature
causes oil to gain body and lose fluidity. Since engine temperatures
range several hundred degrees from cold-weather starting to operating temperature, a lubricating oil must have adequate fluidity at
low temperatures so that it will flow. At the same time, it must have
sufficient body for high-temperature operation.
2. Viscosity ratings. Viscosity of oil is determined by use of a
viscosimeter, a device that can be used to determine the length of
time required for a definite amount of oil to flow through an opening of a definite diameter. Temperature is taken into consideration
during this test, since high temperature decreases viscosity while
low temperature increases viSCOSity. In referring to viscosity, the
lower numbers refer to oils of lower viscosity. SAE lO oil is less
viscous (thinner) than SAE 20 oil, for example.
3. Resistance to carbon formation. Cylinder walls, pistons, and
rings operate at temperatures of several hundred degrees. This temperature acting on the oil films covering walls, rings, and pistons
tends to cause the oil to break down or burn so that carbon is produced. Carbon formation can cause poor engine performance and
damage to the engine. Carbon may pack in around the piston rings,
causing them to stick in the ring grooves. This prevents proper
piston-ring operation, so that blow-by, poor compression, excessive
oil consumption, and scoring of cylinder walls may result. Carbon
may build up on the piston head and in the cylinder head. This
fouls spark plugs, excessively increases compression so that knocking occurs, and reduces engine performance. Carbon may form on
the underside of the piston to such an extent that heat transfer will
be hindered and the piston will overheat. Pieces of carbon may
break off and drop into the oil pan, where they will be picked up by
the lubrication system and will clog oil channels and lines so that
the flow o'f lubricating oil to engine parts is dangerously reduced.
oil must be sufficiently resistant to the heat and
A good l~bricatng
[302]
\
Engine Lubricating Systems
§211
operating conditions in the engine to exhibit a minimum amount of
carbon formation.
4. Resistance to oxidation. When oil is heated to fairly high temperatures and then agitated so that considerable air is mixed with
it, the oxygen in the air tends to combine with oil, oxidizing it.
Since this is the treatment that engine oil undergoes (that is, it is
heated and agitated with or sprayed into the air in the crankcase),
some oil oxidation is bound to occur. A slight amount of oxidation
will do no particular harm; but if oxidation becomes excessive,
serious troubles may occur in the engine. As the oil is oxidized, it
breaks down to form various harmful substances. Some of the
products of oil oxidation will coat engine parts with an extremely
sticky, tarlike material that clogs oil channels and tends to restrict
the action of piston rings and valves. A somewhat different form of
oil oxidation coats engine parts with a varnishlike substance that has
a similar damaging effect on the engine. Even if these substances do
not form, oil oxidation may produce corrosive materials in the oil
that will corrode bearings and other surfaces, causing bearing
failures and damage to other parts. Oil chemists and refineries control the refining processes and may add certain chemicals known as
oxidation inhibitors so that engine lubricating oils resist oxidation.
(Any substance added to the oil is known as an additive. )
5. Foaming resistance. The churning action in the engine crankcase also tends to cause the engine oil to foam, just as an egg beater
causes an egg white to form a frothy foam. As the oil foams up, it
tends to overflow or to be lost through the crankcase ventilator
( §223 ). In addition, the foaming oil is not able to provide normal
lubrication of bearings and other moving parts. To prevent foaming,
antifoaming additives are mixed with the oil.
6. Detergents. Despite the filters and screens at the carburetor
and crankcase ventilator (§223), dirt does get into the engine. In
addition, as the engine runs, the combustion processes leave deposits
of carbon on piston rings, valves, and other parts. Also, some oil
oxidation may take place, resulting in still other deposits. As a
result of these various conditions, deposits tend to build up on and
in engine parts. The deposits gradually reduce the performance of
the engine and speed up wear of parts. To prevent or slow down
the formation of these depOSits, some engine oils contain a detergent
additive.
[303]
Automotive Fuel, Lubricating, and Cooling Systems
§211
The detergent acts much like ordinary hand soap. When you
wash your hands with soap, the soap surrounds the particles of
dirt on your hands, causing them to become detached so that the
water can rinse them away. In a similar manner, the detergent in
the oil loosens and detaches the deposits of carbon, gum and dirt.
The oil then carries the loosened material away. The larger particles
drop to the bottom of the crankcase, but smaller particles tend to
remain suspended in the oil. These impurities, or contaminants, are
flushed out when the oil is changed.
7. Viscosity index. When oil is cold, it is thicker and runs more
slowly than when it is hot. In other words, it becomes more viscous
when it is cooled. On the other hand, it becomes less viscous when
it is heated. In normal automotive-engine operation we do not have
to be too concerned about this change of oil viscosity with changing
temperature. We recognize that the engine is harder to start at low
temperature because the oil is thicker, or more viscous. But until
the engine is cooled to many degrees below zero, we do not have to
take any special steps to start it.
Some oils change viscosity a great deal with temperature change.
Other oils show a much smaller change of viscosity with temperature change. In order to have an accurate measure of how much
any particular oil will change in viscosity with temperature change,
the viscosity-index scale was adopted. Originally, the scale ran
from 0 to 100. The higher the number, the less the _oil viscosity
changes with temperature changes. Thus, an oil with a VI (viscosity
index) of 100 will change less in viscosity with temperature changes
than an oil with a VI of 10. In recent years, special VI-improving
additives have been developed which step up viscosity indexes to as
much as 300. Such an oil shows relatively little change in viscosity
from very low to relatively high temperature.
You could especially appreciate the significance of VI if you were
operating automotive equipment in a very cold climate (say in
northern Alaska). You would have to start engines at temperatures
of as much as 60° below zero (92° below freezing). But once
started, the engines would soon reach operating temperatures that
heat the oil to several hundred degrees. If you could select an oil
~ of a relatively high VI, then it would be fluid enough to permit
starting }\ut would not thin out (or lose viscosity) so much that
[304] \
\
I,
Engine Lubl'icating Systems
§211
lubricating effectiveness would be lost. On the other hand, an oil
with a low VI would probably be so thick at low temperatures that
it might actually prevent starting. But if you could start, it might
then thin out too much as it warmed up.
Actually, VI is of relatively little importance in most parts of the
country. Oil companies make sure that their oils have a sufficiently
high VI to operate satisfactorily in the variations of temperatures
they will meet.
CHECK YOUR PROGRESS
Progress Quiz 10
Once again you have the chance to check up on your progress in the
book. The questions below will help you review what you have just
finished reading on friction and lubrication. Answering the questions recalls to your mind the important points; this helps you remember them.
Completing the Sentences
The sentences below are incomplete. After each sentence there are several words or phn"!ses, only one of which will correctly complete the sentence. Write each sentence down in your notebook, selecting the proper
word or phrase to complete it correctly.
1. The resistance to motion between two bodies in contact is called
load
force
power
friction
dry, smooth, and solid
dry, greasy, and viscous
dry, moist, and greasy
With greasy friction, we have what is called
dry lubrication
borderline lubrication
viscous lubrication
The friction, or resistance to relative motion, between adjacent layers
of liquid is called
dry friction
greasy friction
viscous friction
The three general types of friction bearings are
journal, guide,
and thrust
journal, shaft, and thrust
journal, ball, and
roller
Three types of antifriction bearings are
sleeve, ball, and roller
sleeve, thrust, and ball
ball, roller, and tapered roller
For discussion, viscosity can be divided into two characteristics
flUidity and body
sealing and inhibiting
friction and
fluidity
The ease with which oil flows through oil lines and over bearing
surfaces is called oil
flUidity
body
viscosity
[305]
2. The three classes of friction are
3.
4.
5.
6.
7.
8.
Automotive Fuel, Lubricating, and Cooling Systems
§212
9. Resistance to squeezing out of the oil from between journal and bearing is referred to in terms of oil
fluidity
body
vola-
tility
10. Generally speaking, any substance or chemical added to the oil to
enhance various properties is caned
an inhibitor
an ad-
ditive
a detergent
§212. Water-sludge formation Water sludge is a thick, creamy,
black substance that often forms in the crankcase. It clogs up oil
screens and oil lines, preventing normal circulation of lubricating
oil to the engine parts. This can result in engine failure from oil
starvation.
1. How sludge forms. Water collects in the crankcase in two
ways. Water is one of the products formed during combustion.
Hydrogen in the fuel unites with oxygen in the air to form H20, or
water. Most of this water is exhausted from the engine as vapor
in the exhaust gases. But when the engine is cold, some of it condenses on the cold engine parts. It then works its way past the
piston rings and drops into the crankcase. Another way that water
gets into the crankcase is through the crankcase ventilating system
( §223). When the engine is cold, moisture in the air drawn through
the crankcase by the ventilating system is apt to condense on the
cold engine parts and thus stay in the crankcase.
The water that accumulates is churned up with the lubricating
oil by the action of the moving parts, particularly the crankshaft.
In effect, the crankshaft is a super egg beater that whips the oil and
water together to form the thick, black, mayonnaiselike "goo"
called water sludge. The black color comes from dirt and carbon in
the oiL
2. Sludge-forming operation. If you drive your car for fairly long
distances each time you start it, you will have little trouble with
water sludge. It is true that water will collect in the crankcase for
the first few miles, before the engine warms up. But as soon as the
engine reaches operating temperature, the water evaporates and is
cleared from the crankcase by the crankcase ventilator. However, if
you drive your car only a few miles each time you start it and allow
it to cool off between trips, then the engine will not get warm
enough to throw off the water it has collected in the crankcase.
With each5hort trip, more water collects. And as the water collects,
it is whipped with the oil into water sludge.
[306]
~
f \
Engine Lubricating Systems
§212
Note that it is the short-trip, start-and-stop type of operation
that produces sludge. And this type of operation is far more common than you might think. Studies of car operation in the United
States have shown that about 38 percent of all trips are less than 3
miles in length. Another 24 percent are from 3 to 6 miles long. An
additional 18 percent are from 7 to 13 miles long, and only 20 percent are more than 13 miles in length (see Fig. 11-9).
3. Getting rid of water. As we mentioned, if the car is driven
long enough, the engine will warm up and the water will be
20%
More than
13 miles long
\8%
7-13 miles long
h
24%
3-6 miles long
38%
Less than
3 miles long
Sludge
possibiMy
in
summer
).
Sludge
possibility
in
winter
11-9. Car-trip mileages showing percentage of short, medium, and long
trips (percentages only approximate).
FIG.
evaporated and carried out of the crankcase by the ventilating
system. The number of miles required for this varies from car to
car, and also with the weather. During winter months, the engine
is colder and takes longer (more miles) to warm up. Studies have
shown that during the summer it takes from 3 to 6 miles, on the
average, for the engine to reach operating temperature and begin to
rid itself of water. But during the winter it takes about 14 miles.
When you compare these figures with the average length of trip as
noted in the previous paragraph, you can see that as many as 60
percent of the car trips are too short in summer to rid the engine
of water. In winter as many as 80 percent of the car trips are too
short to rid the engine of water (see Fig. 11-9).
[307]
Automotive Fuel, Lubricating, and Cooling Systems
§213
4. Preventing sludge accumulations. Sludge can lead to engine
failure by blocking oil circulation to engine parts. Thus, it is important to prevent accumulation of sufficient sludge to cause poor
oil circulation. One way of doing this, as noted above, is to take
longer trips in your car. Another way is to drain the crankcase oil
frequently. With frequent oil drains, the sludge never has a chance
to accumulate in really damaging amounts. Section 214 discusses
oil changes.
We have already mentioned
that lubricating oil is rated as to its viscosity by number. An SAE
10 oil is less viscous (lighter) than an SAE 20 oil. An SAE 30 oil
has a comparatively high viscosity. Lubricating oil is also rated in
another way, by what is called service designation. That is, it is
rated according to the type of service for which it is best suited.
There are five service ratings; MS, MM, and ML for gasoline or
other spark-ignition engines, and DC and DS for diesel engines.
The oils differ in their characteristics and in the additives they
contain.
1. MS oil. This oil is for severe service and unfavorable operating
conditions. It is to be used where there are special lubricating
requirements for bearing-corrosion and engine-deposit control because of operating conditions or engine deSign. This includes:
§213. Service ratings of lubricating oil
a. Low operating temperature and short-trip, start-stop driving
conditions, as found in city operation.
b. High-speed highway driving, where oil will become unusually
hot, as during a summer-vacation trip.
c. Heavy-load operation, such as is typical of highway truck
service.
\
\
\
2. MM oil. This oil is for medium service such as:
a. High-speed but fairly short trips.
b. Long trips at moderate speeds and summer temperatures.
c. Operation at moderate cold-air temperatures where the car
is used for both long and short trips.
3. ML oil. This oil is for comparatively light service where most
~ of the trips are longer than 10 miles and where no extremes of air
temperature are encountered.
[308] \ \
\
I.
Engine Lubricating Systems
§214
Caution: Do not confuse viscosity and service ratings of oil. Some
people think that a high-viscosity oil is a "heavy-duty" oil. This is
not necessarily so. Viscosity rating refers to the thickness of the oil;
thickness is not a measure of heavy-duty quality. Remember that
there are two ratings, viscosity and service. Thus, an SAE 10 oil can
be an MS, MM, or ML oil. Likewise, an oil of any other viscosity
rating can have anyone of the three service ratings (MS, MM,
or ML).
4. DS oil. This is an oil for lubricating diesel engines operating
under the most severe service conditions such as:
a. Continuous low temperatures and light loads.
b. Continuous high-temperature, heavy-load conditions.
c. Operation on fuels of high sulfur content or abnormal volatility.
5. DC oil. This is an oil for lubricating diesel engines operating
under comparatively light to normal conditions such as are typical
of most trucking and farm-tractor operations.
§214. Oil changes We have already noted that oil should be
changed periodically to get rid of the water sludge that tends to
accumulate in the crankcase. But that is not the only reason for
changing oil periodically. From the day that the old oil is drained
and new oil put into the crankcase, the new oil begins to lose its
effectiveness as an engine lubricant. This gradual loss of effectiveness is largely due to the accumulation of various contaminating
substances. For instance, during engine operation, carbon tends to
form in the combustion chamber. Some of this carbon gets into the
oil. Gum, acids, and certain lacquerlike substances are also left by
the combustion of the fuel or are produced in the oil itself by the
high engine temperatures. In addition, the air that enters the engine (in the air-fuel mixture) carries with it a certain amount of
dust. Even though the air filter is operating efficiently, it will not
remove all the dust. Then, too, the engine releases fine metal
particles as it wears. All these substances tend to circulate with the
oil. As the mileage piles up, the oil accumulates more and more of
these contaminants. Even though the engine has an oil filter, some
of these contaminants will remain in the oil. Finally, after so many
miles of operation, the oil will be so loaded with contaminants that
[309]
§21S
Automotive Fuel, Lubricating, and Cooling Systems
it is not safe to use. Unless it is drained and clean oil put in, engine
wear will increase rapidly.
Modern engine oils are compounded to fight contamination. They
contain certain chemicals (called additives) which deter corrosion
and foaming and help to keep the engine clean by detergent action.
Yet they cannot keep the oil in good condition indefinitely. As
mentioned in the previous paragraph, after so many miles of service,
the oil is bound to become contaminated and it must be drained.
The actual mileage varies with the type of operation. For dusty or
cold-weather start-and-stop driving, the oil should be changed
every 500 miles or 60 days. For "average" operation, that is, shortrun, start-and-stop service on paved roads with moderate temperatures, mixed with longer trips, the oil should be changed every
1,000 miles. For open highway driving on paved roads, oil should
be changed every 2,000 miles.
NOTE: Automobile manufacturers recommend that the oil be
changed (along with the oil filter) and the air filter cleaned, whenever the car has been subjected to a spell of dusty driving or has
encountered a dust storm. When driving in dusty conditions, the
air and oil filters are apt to get clogged with dust rather quickly.
This means that the oil takes on an excessive amount of dust. This
dust must be removed from the engine by draining the oil, cleaning
the air filters, and replacing the oil filter.
§21 S. Oil consumption Oil is lost from the engine in three ways:
by burning in the combustion chamber, by leakage in liquid form,
and by passing out of the crankcase in the form of a mist. Two
main factors affect oil consumption, engine speed and the amount
that engine parts have worn. High speed produces high temperature, which in turn lowers the viscosity of the oil so that it can more
readily work past the piston rings into the combustion chamber,
where it is burned. In addition, the high speed exerts a centrifugal
effect on the oil that is feeding through the oil lines drilled in the
crankshaft to the connecting-rod journals, so that more oil is fed to
the bearings and subsequently thrown on the cylinder walls. Also,
high speed tends to cause "ring shimmy," a condition in which the
oil-control rings cannot function quite so effectively and will
allow mor~
oil to get into the combustion chamber. Then, too,
crankcase. ventilation (§223) causes more air to pass through the
[310]
\
\
\
\
\
\,
\
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Engine Lubricating Systems
§216
crankcase at high speed, increasing the tendency for oil to be lost
in the form of mist.
As engine parts wear, oil consumption increases. Worn bearings
tend to throw more oil onto the cylinder walls. Tapered and worn
cylinder walls prevent normal oil-control-ring action because the
rings cannot change shape rapidly enough to conform with the
worn cylinder walls as they move up and down. More oil consequently gets into the combustion chamber, where it burns and
fouls spark plugs, valves, rings, and pistons. Carbon formation
aggravates the condition, since it further reduces the effectiveness
of the oil-control rings. Where cylinder-wall wear is not excessive,
installation of special oil-control rings (see Automotive Engines)
reduces oil consumption by improving the wiping action so that
less oil can move past the rings. After cylinder-wall wear has progressed beyond a certain point, the cylinders must be machined and
new rings installed to bring oil consumption down.
Another cause of excessive oil consumption is a cracked vacuumpump diaphragm which passes oil into the intake manifold and
from there into the engine cylinders where it is burned (see §227).
In addition to engine oil, many other
lubricants are required for the automobile. Wherever one part
slides on or rotates in another part, you will find some kind of lubricant at work protecting the parts from undue wear. The steering
system, axles, differential, transmission, brakes, generator, ignition
distributor, and so forth, all use special types of lubricant.
1. Gear lubricants. The gears in transmissions and differentials
must be lubricated with special heavy oils that have sufficient body
to resist oil-film puncture and thereby prevent actual metal-to-metal
contact between the moving gear teeth. On the other hand, the oil
must flow readily even at low temperature so that it does not
"channel" as the gears begin to rotate. Channeling of the oil takes
place if the oil is so thick that the teeth cut out channels in the oil
and the oil does not readily flow to fill the channels.
The lubricant used in hypoid-gear differentials (see Automotive
Transmissions and Power Trains) is subjected to very severe service
since hypoid gears have teeth that not only roll over one another,
but also slide over each other. This combined rolling and sliding
action puts additional pressure on the lubricant. So that the lubri[311]
§216. Automotive lubricants
Automotive Fuel, Lubricating, and Cooling Systems
§216
cant will stand up under this service, it is especially compounded
and contains certain added chemicals that enable it to withstand
much greater pressure than oil alone would withstand. Such lubricants are called extreme-pressure, or EP, lubricants. There are
actually two classifications of these lubricants, the powerful extreme-pressure lubricants for use on heavy-duty applications and
mild extreme-pressure lubricants for use on applications with less
severe requirements.
2. Grease. Essentially, lubricating grease is oil to which certain
thickening agents have been added. The oil furnishes the lubricating action; the thickening agents simply function to hold the oil
in place so that it does not run away. The thickening agents are
usually called soap. This is not the kind of soap we use in washing,
but anyone of several metallic compounds; the type used depends
on the service required of the grease. This is also true of the viscosity
grade (or thickness) of the oil that goes into the grease. For some
services, a relatively light oil is used. For others, a heavy oil is used.
a. Aluminum grease. Aluminum grease contains as thickening agent aluminum compounds. This grease has good adhesive
properties and is widely used for chassis lubrication. While it will
not stand extreme temperatures, it is highly resistant to moisture
and is therefore valuable for lubricating springs and other chassis
parts subjected to road splash.
b. Soda grease. Soda grease contains as thickening agent sodium
compounds that give the grease a thick, fibrous appearance, even
though the grease contains no actual fiber. This grease is often called
fibrous grease, or fiber grease. While it is less resistant to moisture
than some other greases, it is very adhesive and clings tightly to
rotating parts. It is therefore valuable for rotating parts such as
wheel bearings and universal joints.
c. Calcium grease. Calcium grease uses calcium compounds as
thickening agent. This grease is often known as cup grease and is
used in lubricating parts supplied with grease cups. It has a tendency to separate into liquid oil and solid soap at high temperatures.
d. Mixed greases. Each of the various greases mentioned above
has special valuable characteristics. Mixed greases are blends of
these different greases. This blending produces greases that can
better meet the requirements of certain specific applications. Actually, the ,automotive mechanic does not have to worry about the
[312]
\
I'
\
\
Engine Lubricating Systems
~217
composition of the various greases since the automotive manufacturer and the petrolemn company have worked together to produce oils and greases exactly suited for the various parts and places
requiring lubrication on the automobile. As long as the automotive
mechanic follows the automobile manufacturers' recommendations,
he is sure of putting the right lubricant in the right place on the car.
§217. Types of lubricating systems Three types of lubricating systems have been used. These are (I) splash, (2) pressure feed, and
11-10. Splash lubricating system used on an in-line engine. An oil p1.:mp
maintains the proper level of oil in the tray under the connecting rods.
FIG.
(3) combination splash and pressure feed. The latter two types predominate in modern engines.
1. Splash. In the splash lubricating system, dippers on the connecting-rod bearing caps enter oil trays in the oil pan with each
crankshaft revolution (Fig. 11-10). The dippers pick up oil for the
[313]
Automotive Fuel, Lubricating, and Cooling Systems
§217
connecting-rod bearings and splash oil to the upper parts of the
engine. The oil is thrown up as droplets and £ne mist and provides
adequate lubrication to valve mechanisms, piston pins, cylinder
walls, and piston rings. In the engine shown in Fig. 11-10, an oil
pump is used to deliver oil to the trays beneath the connecting rods.
2. Pressure feed. In the pressme-feed lubricating system (Figs.
11-11 to 11-14), the oil is forced by an oil pump to the various parts
ll-ll. Lubrication
system of a six-cylinder
overhead-valve engine.
Arrows show oil How
to the moving parts in
the engine. (Ford Division of Ford Motor
FIG .
Company)
of the engine requiring lubrication. The oil from the pump enters
an oil line (or a drilled header, or channel, or gallery, as it is
variously called), and from the oil line it flows to the main bearings
and camshaft bearings. The main bearings have oil-feed holes or
grooves that feed oil into drilled passages in the crankshaft. The oil
flows through these passages to the connecting-rod bearings. From
there, on tnany engines, it flows through holes drilled in the connecting rCi>d to the piston-pin bearings. Cylinder walls are lubricated
[314J
/,
;
\.
Engine Lubricating Systems
§217
by oil thrown off from the connecting-rod and piston-pin bearings.
Some engines have oil-spit holes in the connecting rods that
index with drilled holes in the crankpin journals with each revolution. As this happens, a stream of oil is thrown onto the cylinder
walls (Fig. 11-14) . On overhead-valve engines the rocker arms and
other valve-mechanism parts are lubricated by an oil line that feeds
into the hollow rocker-arm shaft.
11-12. Lubrication system of a V-8 overhead-valve engine. Arrows show
oil Row to moving parts in engine. (Mercury Division of Ford Motor Company)
FIG.
3. Combination splash and pressure-feed system. The combination splash and pressure-feed lubricating system depends on oil
splash to lubricate some engine parts and on pressure feed to lubricate other engine parts. An example of this type of system is shown
in Fig. 11-15. In this engine the oil is supplied under pressure to the
main bearings, the camshaft bearings, and the valve mechanisms.
The connecting-rod bearings are lubricated by means of dippers on
the rod bearing caps that dip into troughs in the oil pan. At high
[315)
Automotive Fuel, Lubricating, and Cooling Systems
§217
FIG. 11-13. Full-pressure lubrication system used on a V-8 overhead-valve
engine. (Buick Division of General Motors Corporation)
OIL- SPIT
~
FIG. 11-14. ~ctionalS
lubricate p~ton
Division of ~enral
[316]
/\
view of a connecting rod and pi~ton,
showing oil hole to
pin and oil-spit hole to lubricate cylinder wall. (Oldsmobile
Motors Corporation)
\.
Engine Lubricating Systems
§217
FIG. 11-15. Six-cylinder engine that uses combination splash and pressurefeed lubrication system. (Chevrolet Motor Division of General Motors Corporation)
11-16. Method of lubricating connecting-rod bearing of engine that is
shown in Fig. 11-15. (Chevrolet Motor Division of General Motors Corporation)
[317]
FIG.
Automotive Fuel, Lubricating, and Cooling Systems
§218
speed, oil streams are thrown up from the oil troughs tlu'ough oil
nozzles (Fig. 11-16), and these strike the dippers on the rod bearing caps to provide adequate lubrication for the connecting-rod
bearings. Cylinder walls, piston-pin bearings, and piston rings are
lubricated by oil spray thrown off by the connecting rods.
§218. Oil pumps The oil pumps most widely used in pressure-feed
lubricating systems are shown in Figs. 11-17 to 11-21. The gear
pump shown in Figs 11-17 and 11-18 depends upon the meshing of
a pair of gears to produce the movement of the oil through the
pump. As the gears rotate, the spaces between the gear teeth are
11-17. Gear-type oil pump
with built-in oil-pressure relief
valve. Arrows indicate direction of
oil through pump.
FIG.
FIG. 11-18. Disassembled view of a
gear-type oil pump.
GASKET
IDLER GEAR
~
IDLER
LOCK WASHER~T
CAP SCREW ___.,
[318]
\
PIN
Engine Lubricating Systems
§218
filled with oil from the oil inlet. The oil is carried around to the oil
outlet, and here the gear teeth mesh to force the oil out from between the teeth. The oil that is forced out is thereby forced to flow
through the oil outlet and from there to the various parts of the
engine.
The rotor-type pump uses an inner and an outer rotor instead of
two gears (Figs. 11-19 to 11-21). This pump is also called an [0
pump ( for inner-outer rotor ) or a dual-1'oto'!' pump. In the assembled pump the inner rotor fits inside the outer rotor as shown in
Fig. 11-21. The inner rotor rotates, causing the outer rotor to rotate
Oil PUMP AND DISTRIBUTOR DRIVE GEAR
(...J
Oil PUMP BODY
~
OIL PUMP ROTOR (INNER)
\
ROTOR PIN
/
COVER GASKET
DRIVE GEAR PIN
OIL PUMP DRIVE SHAFT
11-19. Disassembled view of a rotor-type oil pump. (Dodge Division of
Chrysler Corporation)
FIG.
with it. When this happens, oil enters the spaces between the rotors
on the side of the pump where these spaces increase in size. Then,
as these spaces move further around, the inner rotor lobes move
into the spaces and squeeze the oil out. The oil is forced out of the
pump through the oil outlet. Note that this pump works almost
exactly like the gear pump, the essential difference being that in
one, oil is squeezed from between gear teeth, and in the other, oil
is squeezed from between the outer rotor and inner rotor lobes.
Oil pumps are usually driven from the engine camshaft, from the
[319]
Automotive Fuel, Lubricating, and Cooling Systems
§219
same spiral gear on the camshaft that also drives the ignition distributor. On some engines, the driven gear is assembled on the
distributor shaft. On others, the driven gear is assembled to the oilpump shaft. On both types, the two shafts are coupled by a tongue
DISTRIBUTOR lOWER DRIVE
SHAFT AND GEAR
Pump
! body
RElIEF VALVE PLUNGER
lr
RELIEf VALVE SPRING
Oil SEAL
~/RElIF
RING (LARGE) "
I
Inner
rotor
VALVE PLUG
FIG. 11-21. Rotor-type oil pump with
cover removed so fit of inner and outer
rotors to each other can be seen.
(Plymouth Division of Chrysler Corporation)
FIG. 11-20. Disassembled view of a
rotor-type oil pump which has a builtin pressure relief valve. (De Soto
Division of Chrysler Corporation)
on one and a groove in the end of the other. Figures 11-12, 11-15,
and 11-22 show the location of the oil pmnp in different engines.
In any pressure-feed lubrication system, a relief
valve must be incorporated to prevent the building up of excessively high oil pressures during high-speed or cold-weather
operation. The relief valve may be incorporated in the oil pump as
shown in fig . 11-17. On this unit the spring-loaded ball is forced
off its sea..,t 'when excessive pressures are approached, permitting oil
[320]
\
§219. Relief valve
\
\
Engine Lubricating Systems
§219
to flow back into the oil pan through a bypass instead of being
forced through the pressure-feed system. The relief valve may be
located in other places in the oil line. One type, shown in Figs. 1123 and 11-24, has the valve located in the cylinder block where it
11-22. End sectional view of an L-head engine showing location of oil
pump, oil filter, and oil-pressure relief valve. Direction of oil flow is shown
by arrows. (Dodge Division of Chrysler Corporation)
FIG.
is readily accessible. In operation the pressure-relief valve bypasses
a considerable part of the oil from the oil pump, allowing it to return to the oil pan. The oil pump can normally deliver much more
oil than the lubrication system requires. This is a safety factor that
assures delivery of adequate oil under extreme operating conditions.
[321]
Automotive Fuel, Lubricating, and Cooling Systems
§220
FIG. 11-23. Location of oil-pressure relief valve in cylinder block. 1, cap; 2,
gasket; 3, spring; 4, plunger. (Plymouth Division of Chrysler Corporation)
10 Oil
FILTER
CLOSED
FROM
OIL FILTER
TO Oil
FILTER
FROM
OIL FILTER
OPEN
11-24. Action of oil-pressure relief valve. With the valve closed, no oil is
bypassed through the oil filter. But with the valve opened, oil is bypassed
through the oil filter as well as past the valve, and flows back into the oil pan.
(Plymouth Division of Chrysler Corporation)
FIG.
§220. Oil filters Carbon particles, dust, and dirt become mixed
with the lubricating oil during the operation of the engine. The
heavier particles usually drop to the bottom of the oil pan, but
some of the smaller particles may travel through oil lines to bearing
surfaces, where they embed, causing damage to bearings and
journals. To reduce damage from this cause, many lubl'ication
systems utilize an oil filter that circulates all or some of the oil
from the pump through tightly packed masses of filtering material.
The filtering material traps particles of foreign material but permits
the oil to 'Pass through. Filters are two types: those that filter part
(322]
/\
\
Engine Lubricating Systems
§220
of the oil from the oil pump, called bypass filters, and those that
filter all the oil in circulation through the system, called full-flow
filters.
1. Bypass filters. The bypass oil filter (Figs. 11-25 and 11-26) is
in most common use. The supply line from the oil pump is so connected as to permit only part of the oil passing through to flow to
the oil filter. The remainder of the oil bypasses the oil filter and
MOUNTING
BRACKETS
\F1L TERING ELEMENT
l OR CARTRIDGE
OIL OUTLET
FIG.
11-25. Oil filter with replaceable filtering element (or cartridge).
circulates in the usual manner through the various oil lines to the
engine parts. Even though only part of the oil passes through the
filter, enough does flow (when the filter is clean) to produce adequate cleaning of the oil.
2. Full-flow filters. The full-flow filter is so deSigned and connected that all the oil from the oil pump passes through it before it
enters the oil lines to the engine parts. The filter used in the engine
shown in Fig. 11-13 is of the hlll-flow type. This type of filter contains a spring-loaded valve that serves as a protection against oil
starvation in case the filter becomes so loaded with contaminants
that it will not pass enough oil. When this happens, the spring[323]
Automotive Fuel, Lubricating, and Cooling Systems
§220
FIG. 11-26. Heavy-duty type of oil filter with replaceable element (cartridge).
CAC Spark Plug Division of General Motors Corporation)
4. Cloth
7. Drain
1. Inlet
9. Spring
2. Screen
5. Collector tube
8. Cover nut
10. Gasket
3. Filter element
6. Outlet
FIG. 11-27. Full-flow oil screen, or filter. All oil from oil pan passes through filter
before reachipg oil pump and other working parts. (Pontiac Motor Division of
General Mq_tiJrs Corporation)
\
(3241
\.
Engine Lubricating Systems
§221
loaded valve is opened (by the oil pressure from the pump) and it
bypasses the filter so that enough oil can flow to assure adequate
lubrication of engine parts. A different sort of full-flow filter, or oil
screen, is shown in Fig. 11-27. This is Simply a series of screens
through which the oil must pass on its way to the oil pump.
3. Filter-element replacement. As a filter becomes clogged with
foreign particles and impurities, its efficiency decreases. In the
bypass filter less and less oil passes through the filter, until finally the
filter is practically inoperative and all oil is flowing through the
bypass. The same thing takes place in the full-flow filter, with the
valve opening to permit the oil to bypass the filter. Before this happens, the filter must be replaced. In some types the complete filter
is replaced. In others the filter element only is removed from the
filter case and replaced. In the filter-screen arrangement as shown
in Fig. 11-27, it is desirable to clean the screens periodically.
4. Floating oil intake. In many engines a floating oil intake is
used through which oil is pulled to the oil pump (Fig. 11-28). As
FIG. 11-28. Floating oil intake.
the oil level changes, the floating intake rises or falls , continuing to
take oil from the top. Foreign particles that have entered the oil
tend to drop to the bottom of the oil pan and are not picked up by
the floating intake. Floating oil intakes are shown on several
engines in Figs. 11-11, 11-12, and 11-22.
§221 . Oil coolers Oil coolers are sometimes used to provide additional cooling of the oil to that which is obtained by means of
ribs and fins in the engine oil pan. One type consists of a small
radiator mounted on the side of the engine block, through which
oil and water circulate. The water passes through the tubes, and
the oil flows around the tubes. The water thus absorbs heat from
the oil and carries it to the engine radiator, where it is in turn
given to the cooling air passing through the radiator. Another
design uses a small section of the engine radiator as a cooling device
[3251
Automotive Fuel, Lubricating, and Cooling Systems
§222
for the oil. The oil is circulated through this section of the radiator,
thus giving up its excess heat to the passing air.
§222. Oil-pressure indicators The oil-pressure indicator provides
the driver with an indication of the oil pressure in the engine. This
gives warning if some stoppage occurs in the lubrication system
that prevents delivery of oil to vital parts. Oil-pressure indicators
are of two general types, pressure expansion and electric resistance.
The latter is the more commonly used.
GEAR SECTOR
NEEDLE
GEAR SECTOR. PIVOT
'.'
OIL--'·
r
ITUBE FROM
lLUBRICATION SYSTEM
FIG. 11-29. Bourdon tube and linkage to indicating needle used in pressureexpansion oil-pressure indicator.
1. Pressure expansion. The pressure-expansion indicator uses a
hollow Bourdon (curved) tube that is fastened at one end and
free at the other. The oil pressure is applied to the curved tube
through an oil line from the engine and causes the tube to straighten
out somewhat as pressure increases (Fig. 11-29). This movement is
transmitted to a needle by linkage and gears from the end of
the tube. The needle moves across the face of a dial and registers
the amount of oil pressure.
2. Elec'tfic. Electrically operated oil-pressure indicators are of
two type.s, 'the balanCing-coil typ>c and the bimetal-thermostat type.
[326]
\
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Engine Lubricating Systems
~2
The balancing-coil type makes use of two separate units, the engine
unit and the indicating unit (Figs. 11-30 and 11-31 ). The engine
unit (Fig. 11-30) consists of a variable resistance and a movable
contact (Fig. 11-31) that moves from one end of the resistance to
the other in accordance with varying oil pressure against a
diaphragm. As pressure increases, the diaphragm moves inward,
causing the contact to move along the resistance so that more
resistance is placed in the circuit between the engine and indicating
IGNITION
SWITCH
11-30. Engine unit of electricresistance oil-pressure indicator. Housing has been cut away so resistance
and movable contact can be seen.
(AC Spark Plug Division of General
Motors Corporation)
FIG.
FIG. 11-31. Electric circuit of electricresistance oil-pressure indicator.
units. This reduces the amount of current that can flow in the
circuit. The indicating unit consists of two coils that balance each
other in a manner similar to electrically operated fuel gauges (§38).
In fact, this type of indicator operates in the same manner as the
fuel indicator, the only difference being that the fuel indicator uses
a float that moves up or down as the gasoline level changes in the
gasoline tank, while in the oil-pressure indicator changing oil
pressure operates a diaphragm that causes the resistance change.
Refer to the discussion on the operation of the fuel-indicator gauge
(§38) .
The bimetal-thermostat type of oil-pressure indicator is similar
to the bimetal-thermostat fuel gauge (§38). The dash units are
[327J
Automotive Fuel, Lubricating, and Cooling Systems
§223
practically identical. The engine unit of the oil-pressure indicator,
while somewhat different in appearance from the tank unit of the
fuel gauge, operates in a similar manner. Varying oil pressure on
a diaphragm distorts the engine-unit thermostat blade varying
amolmts, and this distortion produces a like distortion in the dashunit thermostat blade, causing the oil pressure to be registered on
the dash unit.
FIG. 11-32. Crankcase ventilating system of a six-cylinder engine. Flow of air
is shown by arrows. Air enters through the combination oil filler and breather
cap. (Ford Division of Ford Motor Company)
§223. Crankcase ventilation As has already been pointed out, water
constantly appears in the crankcase as a result of normal engine
operation. Since the pistons are constantly moving up and down
in the cylinders, the total volume of air in the crankcase is
constantly changing. This means that air is being drawn in and expelled. If the engine parts are cold, moisture will condense out of
the air. This water tends to mix with the lubricating oil in the
crankcase ~nd
form sludge (§212). The oil is also diluted by liquid
gasoline that seeps down past the piston rings and enters the
crankcase\ After the engine has reached operating temperature,
[328]
I \
\.
Engine Lubricating Systems
§223
the water and gasoline will vaporize and, if the crankcase is
ventilated, will pass harmlessly out into the air. Crankcase ventilation is generally accomplished by utilizing the natural whirling
motion of the air in the crankcase, caused by the rotation of the
crankshaft (Fig. 11-32). The air that enters is usually screened
through some filter material that helps prevent dust from entering
the crankcase.
AIR
VAPOR
FIG. 11-33. Crankcase ventilating
system in an overhead-valve engine.
FIG.
11-34. Positive crankcase ventila-
tion.
Figure 11-33 shows, in end sectional view, the crankcase ventilating system of an overhead-valve engine. Figure 11-34 shows a
system that assures positive ventilation of the crankcase. In this
system, air is drawn directly into the crankcase through an air
filter that is similar to (though smaller than) a carburetor air
cleaner. Mter circulating tlu-ough the crankcase and picking up
vapors, the air passes upward to the valve cover. From there, it goes
through a tube connected to the intake manifold. Intake-manifold
vacuum produces the air movement. The tube to the intake manifold has a valve, or restriction, that prevents excessive amounts of
[329]
Automotive Fuel, Lubricating, and Cooling Systems
§224
air from bleeding into the intake manifold. If this happened, the
air-fuel mixtme would be excessively leaned out and poor engine
performance would result.
§224. Oil-level indicators In order to determine how much oil remains in the oil pan, oil-level sticks, or "dip sticks," as they are
called, are used. The dip stick is so placed at the side of the engine
that it protrudes down into the oil (Fig. 11-35). It can be with-
FIG.
11-35. Location of oil-level stick, or dip stick, in engine.
drawn to determine how high the oil is in the pan. When oil is
added, it is poured into the oil pan through the oil-filler tube on the
side of the engine. The filler tube often serves as the air inlet for
the crankcase ventilation system.
CHECK YOUR PROGRESS
Progress Quiz 11
Here is\{our chance to check up on how well you remember the material you \have
just finished studying on lubricating systems. The questions
,
[330]
\
Engine Lubricating Systems
§224
that follow help you review the material and fix it more firmly in your
mind.
Completing the Sentences
The sentences below are incomplete. After each sentence there are
several words or phrases, only one of which will correctly complete the
sentence. Write each sentence down in your notebook, selecting the
proper word or phrase to complete it correctly.
1. Water sludge forms in the crankcase from the mixing of
2.
3.
4.
5.
6.
7.
8.
9.
10.
water
and fuel
water and oil
water and air
Water sludge is most apt to form during
cold weather
warm weather
changeable weather
The type of car service that is most apt to result in the formation of
water sludge is
short-trip operation
long-trip operation
trips longer than 14 miles
The three service ratings of lubricating oil for gasoline engines are
SAE 10, 20, and 30
DS, DC, and DL
MS, MM, and ML
For so-called "average" car operation the oil should be changed every
500 miles
1,000 miles
2,000 miles
Two possible ways that oil might be lost from the engine are by
burning and leakage
dilution and mixing
splash and
pressure
A grease is essentially a thickening agent to which
aluminum
soda
calcium
oil
has been added.
Two types of automotive-engine lubricating systems are
high
and low pressure pressure and vacuum
pump and graVity
splash and pressure
Two types of oil filter are
pass and bypass
bypass and
fullflow
pressure and gravity
Two types of electric Oil-pressure indicators are
balancing-coil
and bimetal-thermostat
pressure-expansion and thermostat
balancing-coil and pressure-expansion
CHAPTER CHECKUP
NOTE: Since the following is a chapter review test, you should review the chapter before taking the test.
You are nearing the end of the book and have only lubricating-system
servi.ce and the cooling system still to cover. You have been making fine
progress, and with only a little more effort you will have this volume
completed. The material on the engine lubricating system that you
have just finished will be of great help to you when you go into the shop.
The checkup below will give you a chance to test yourself on how well
[331]
Automotive Fuel, Lubricating, and Cooling Systems
you remember this material. If you are not sure of an answer, reread the
pages that will give you the answer. Reviewing the chapter and writing
down the answers will help you remember the important points.
Completing the Sentences
The sentences below are incomplete. After each sentence there are
several words or phrases, only one of which will correctly complete the
sentence. Write each sentence down in your notebook, selecting the
proper word or phrase to complete it correctly.
1. The type of friction commonly present in an automotive engine is
dry friction
greasy friction
viscous friction
2. Other factors being equal, the bearing having the least friction is the
friction bearing
antifriction bearing
sleeve bearing
3. Almost all bearings used in automotive engines are
friction
bearings
antifriction bearings
guide bearings
4. In addition to lubricating engine parts to minimize wear and power
loss and acting as a cooling agent, the lubricating oil must
improve carburetion, aid fuel pump, and seal
improve clearances,
cool engine, and clean
absorb shocks, seal, and clean
5. A measure of how much the viscosity of an oil changes with temperature changes is made by the
viscosity-index scale
viscosity scale
detergent-viscosity scale
reduce
6. One way to prevent the formation of water sludge is to
engine temperature
reduce engine speed
make longer
trips
7. If you use your car during the winter for short-trip, start-and-stop
MM oil
ML oil
service, you should use
MS oil
DS oil
8. If you use your car during the winter months for short-trip, start-andstop service, to be on the safe side you should change oil every
500 miles or 60 days
1,000 miles
2,000 miles
9. Two types of oil pump are
vacuum and pressure
dual
rotor and gear
gear and diaphragm
pressure and vacuum
10. Two types of oil-pressure indicator are
pressure expansion and electric
float and pressure
Unscrambling the Purposes of Oil
When the two lists below are unscrambled and combined, they will
form a list of the jobs that oil does in the engine and the reasons that
these jobs mllst be done. To unscramble the lists, take one item at a time
from the list on the left, and then find the item from the list on the right
that goes With it. For examples of how this is done, refer to "Unscram-
[332]
\
.\
.
\
\
\
'\
Engine Lubricating Systems
bling the Jobs" at the end of Chap. 3. Write the list down in your notebook.
lubricate
lubricate
act as cooling agent
resist squeezing out
cover rings
pick up dirt
to absorb shock loads in bearings
to serve as cleaning agent
to minimize power loss
to form seal between rings and wall
to minimize wear
to remove heat from engine parts
Unscrambling the Properties of Oil
Below, in scrambled form, are two lists giving the properties of oil
and the reasons for or definitions of these properties. To unscramble the
lists, refer to the directions given in the previous test.
viscosity
body
fluidity
heat resistant
oxidation resistant
foam resistant
detergent ability
viscosity-index rating
viscosity change with temperature
to minimize foaming
tendency to resist flowing
resistance to oil-film puncture
ease with which oil flows
to minimize carbon formation
to minimize oil breakdown
to help keep engine clean
Unscrambling the Service Ratings of Oil
Below, in scrambled form, are two lists giving the service ratings of
oil and what they mean. To unscramble the lists, refer to the directions
given for "Unscrambling the Properties of Oil," above.
MS
MM
ML
DS
DC
for medium automotive service
for heavy-duty or severe diesel
service
for light or normal diesel service
for severe or heavy-duty automotive service
for light automotive service
Definitions
In the following, you are asked to write down certain definitions of
important terms, purposes of lubrication-system components, and so on.
The act of writing down these answers in your notebook will help you
remember them. Also, it makes your notebook a more valuable reference
for you to look at when you need to recall important facts about the
automobile.
[333]
Automotive Fuel, Lubricating, and Cooling Systems
1. List and define the three classes of friction.
2. Define and give examples of friction and antifriction bearings.
3. List six purposes of the engine oil, and explain how the oil accomplishes these purposes.
4. Explain how body and fluidity affect the action of the lubricating oil.
5. Name some properties that a good lubricating oil must have, and
explain what these properties are.
6. List the three ways in which oil may be lost from the engine.
7. What are the two main factors affecting oil consumption?
8. Explain why higher engine speeds increase oil consumption.
9. List and describe different lubricating greases used in automobiles.
10. List and describe the three different types of automobile lubrication
systems.
11. Name and describe the operation of the two most widely used types
of automotive oil pumps.
12. What is the purpose of the relief valve?
13. What is the purpose of the oil filter?
14. Name and describe the operation of the two types of electrically operated oil-pressure indicators.
15. Describe the purpose and operation of the crankcase ventilating
system.
16. Where are oil-level indicators usually located and how are they used?
SUGGESTIONS FOR FURTHER STUDY
Examine various engines, oil pumps, filters, and other lubrication-system components so you can better understand how the oil is circulated
from the crankcase to the various engine parts. Study the illustrations and
descriptions of lubrication systems in all the car shop manuals you can
get your hands on. Go to your local library and see what you can find on
the subject of lubricating oils, greases, and petroleum refining methods.
Write down in your notebook any important facts you come across that
you want to be sure to remember.
\
\
\
\
\
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\
12: Lubricating-system sel'vice
THE PURPOSE of this chapter is to discuss in detail the services
required by the engine lubricating system. It must be remembered
that the lubricating system is actually an integral part of the engine
and that the operation of one depends upon the operation of the
other. Thus, the lubricating system, in actual practice, cannot be
considered as a separate and independent system; it is part of the
engine. The servicing procedures that follow should be considered
to be an extension of the engine-servicing procedures outlined in
another book in the McGraw-Hill Automotive Mechanics Series
(Automotive Engines).
§225. Testing instruments The lubricating system is an integral part
of the engine, and, consequently, any test of the oiling system involves testing the engine. ' Thus the pressure tester for detecting oil
leaks in the pressure-feed type of lubrication system also detects
excessively worn bearings, since worn bearings have excessive
clearances that allow oil leakage. Various lubricating-system chek~
and the troubles encountered in the lubricating system and with
lubricating oils are discussed in following paragraphs.
The pressure tester for testing the pressure-feed type of lubricating system (Fig. 12-1) consists of a pressure tank partly filled with
medium oil, with fittings and hose for attaching the tank to a source
of compressed air and to the engine lubrication system. The tester
is connected to the outlet line of the oil pump or to any point in
the system where oil pressure can be applied. Then, with the oil pan
removed so that the main and connecting-rod bearings can be seen,
air pressure is applied to the tester tank. This forces oil under
pressure into the engine oil lines. Any oil leak, as well as tight
bearings or oil-passage obstructions, can thus be readily detected.
In addition, a worn bearing will be disclosed, since it would permit
1
See Automotive Engines.
[335]
Automotive Fuel, Lubricating, and Cooling Systems
§226
the escape of a steady stream of oil around the ends of the bearing.
One manufacturer of an oil-leak detector specifies that with SAE
30 oil and 25 pounds of air pressure, 20 to 150 drops of oil per
minute escaping from a bearing indicates that the bearing condition
is satisfactory. Less than 20 drops of oil per minute indicates a
tight bearing or an obstruction in the oil passage. More than 150
drops per minute indicates worn bearings.
NOTE: When an oil-passage hole in the crankshaft indexes with
an oil-passage hole in a bearing, considerable oil will be fed to the
bearings, and the oil will stream out as though the bearing were
FIG. 12-1. Pressure-type bearing oil-leak detector. (Federal-M ogttl Corpora-
tion)
worn. The crankshaft must be rotated somewhat to move the holes
out of index before the test can be made. Bearings that have annular
grooves into which oil is constantly fed cannot be tested by this
method.
Most engines use a bayonet type
of oil-level gauge (the dip stick) that can be withdrawn from the
crankcase to determine the oil level in the crankcase (see Fig.
11-35) . The gauge should be withdrawn, wiped clean, reinserted,
and again withdrawn so that the oil level on the gauge can be seen.
The gauge is usually marked to indicate the proper oil level. The
appearapce of the oil should be noted to see whether it is dirty,
thin, or thick. A few drops of oil can be placed between the thumb
and fin \ ~ ers
and rubbed, to detect dirt or to find out whether the
[336] 1\
§226. Lubricating-system checks
\
Lubricating-system, Service
§227
oil has sufficient body, that is, whether it is sticky. If the oil level
is low, oil should be added to the crankcase. If the oil is thin or
dirty, it should be drained and the crankcase refilled with clean oil.
§227. Trouble tracing in lubricating system Relatively few troubles
occur in the lubricating system that are not intimately related to
engine troubles. Another book in the McGraw-Hill Automotive
Mechanics Series (Automotive Engines) discusses engine troubles.
Valve Stem Guides
Piston
Cylinder Bore
Fron! End Platf'
Chain Casf'
Cover Gaskets
Cannectinq Rod
Bearinq
and
~_-
Rpar Main
Bearinq
Rear Main
Bearinq Oil Spa/
Crankshaft Oil·
way ta Connect·
inQ Rod
Front Main Bearinq'
Oil Seal
Front Main Beorinq
.
Crankshoft Journal
FIG. 12-2. Partial sectional view of engine showing points where oil may be
lost. (Federal-Mogul Corporation)
The lubricating-system troubles most commonly experienced are
discussed below.
1. Excessive oil consumption. Most lubricating-system troubles
produce excessive oil consumption, the cause of which is not
always easy to determine. As was explained in §215, oil is lost from
the engine in three ways: by burning in the combustion chamber,
by leaking in liquid form, and by passing out of the crankcase
through the crankcase ventilating system in the form of vapor or
mist. Figure 12-2 shows some of the places at which oil may be lost
[337]
Automotive Fuel, Lubricating, and Cooling Systems
§227
\
from an engine. Excessive oil consumption is not difficult to detect;
the need to add oil frequently to maintain the proper oil level
in the crankcase makes the condition obvious. The actual amount
of oil consumption can be accurately checked by filling the crankcase to the correct level with oil, operating for several hundred
miles, and then measuring the additional oil that must be added to
bring the oil back to the original level.
External leaks can often be detected by inspecting the seals
around the oil pan, valve-cover plate, and timing-gear housing, and
at oil-line and oil-filter connections. Presence of excessive amounts
of oil indicates leakage. Some authorities suggest that a white cloth
attached to the underside of the engine during a road test will be
helpful in determining the location of external leaks.
The burning of oil in the combustion chamber usually produces
a bluish tinge in the exhaust gas. Oil can enter the combustion
chamber in three ways: through a cracked vacuum-pump diaphragm
when the car is equipped with a combination fuel and vacuum
pump, through the clearance between intake-valve guides and
stems, and around the piston rings.
a. Checking vacuum pump. When the exhaust smoke from a car
equipped with a combination fuel and vacuum pump has a bluish
tinge, the vacuum pump should be checked to see if the diaphragm
is cracked. This can be easily done by operating the windshield
wiper and then quickly accelerating the engine. If the windshield
wiper stops during acceleration, it indicates that the vacuum-pump
diaphragm is cracked. Oil can pass through the crack into the
combustion chamber. If the windshield wiper continues to operate
at normal speed during acceleration, the vacuum-pump diaphragm
is not the cause of excessive oil consumption. This test does not,
of course, apply to a car without a combination fuel and vacuum
pump.
b. Intake-valve guides. A second means by which oil can enter
the combustion chamber is through clearance caused by wear between the intake-valve guides and stems. When clearance is excessive, oil will be sucked into the combustion chamber on each
intake stroke. The appearance of the underside of an intake valve
provides a clue to the condition of its stem and the guide. If the
underside of the intake valve has excessive amounts of carbon, the
valve guid~
and pOSSibly the valve stem are excessively worn. Some
[338]
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Lubricating-system Service
§227
of the oil that passes around the valve remains on the underside
to form carbon. When this condition is found, it is usually necessary
to install valve packing or a new valve guide. A new valve also may
be required.
c. Rings and cylinder walls. Probably the most common cause
of excessive oil consumption is passage of oil to the combustion
chamber between the piston rings and the cylinder walls (sometimes known as oil pumping). This results from worn, tapered, or
out-of-round cylinder walls, or from worn or carboned piston rings.
In addition, when the bearings are worn, excessive amounts of
oil are thrown on the cylinder walls, so that the piston rings, unable
to control all of it, allow too much oil to work up into the combustion chamber.
d. Speed. Another factor that must be considered in any analysis
of oil consumption is engine speed. High speed produces high oil
temperatures and thin oil. This combination causes more oil to be
thrown on the cylinder walls. The piston rings, moving at high
speed, cannot function so effectively, and more oil works up into
the combustion chamber past the rings. In addition, the churning
effect on the oil in the crankcase creates more oil vapor or mist
at high speed, and more oil is lost through the crankcase ventilation
system. Tests have shown that an engine will use several times as
much oil at 60 mph (miles per hour) as at 30 mph.
2. Low oil pressure. Low oil pressure can result from a weak
relief-valve spring, a worn oil pump, a broken or cracked oil line,
obstructions in the oil lines, insufficient or excessively thin oil, or
bearings so badly worn that they can pass more oil than the oil
pump is capable of delivering. A defective oil-pressure indicator
may record low oil pressure.
3. Excessive oil pressure. Excessive oil pressure may result from
a stuck relief valve, an excessively strong valve spring, a clogged
oil line, or excessively heavy oil. A defective oil-pressure indicator
may record high oil pressure.
4. Oil dilution. When the car is used for short runs with sufficient
time between nIllS to allow the engine to cool, the engine is operating most of the time on warm-up. Under this condition, the oil will
be subject to dilution by unburned gasoline seeping down into
the crankcase past the piston rings. In addition, water will collect
in the crankcase, since the engine does not operate long enough
[339]
§228
Automotive Fuel, Lubricating, and Cooling Systems
at temperatures high enough to evaporate the water. These two
substances, water and gasoline, will change the lubricating properties of the oil by forming sludge (§212), and engine parts will
wear more rapidly. When this type of operation is experienced, the
oil should be changed at frequent intervals to remove the water
sludge and diluted oil.
§228. lubricating-system service There are certain lubricatingsystem service jobs that are done more Or less automatically when
an engine is repaired. For example, the oil pan is removed and
cleaned during such engine-overhaul jobs as replacing bearings or
rings. When the crankshaft is removed, it is the usual procedure to
clean out the oil passages in the crankshaft. Another book in the
McGraw-Hill Automotive Mechanics Series (Automotive Engines)
describes the various engine-servicing jobs. Following sections describe such lubricating-system service jobs as changing oil, cleaning
the oil pan, servicing the relief valve, changing or cleaning the oil
filter, and servicing the oil pump and the oil-pressure indicator.
§229. Changing oil Standard practice is to change the engine oil
at 500-, 1,000-, or 2,000-mile intervals, according to the type of
operation (§214). Oil filters installed in the system tend to reduce
the frequency with which oil will require changing. But they do
not eliminate the need for oil changes. Oil should be changed more
frequently during cold weather, particularly when short-trip operation predominates. With short-trip operation, the engine operates
cold a greater part of the time, and this increases the chances for
water sludge to form. More frequent oil changes will remove this
sludge before dangerous amounts can accumulate. When the car is
operated on very dusty roads, the oil should be changed more frequently. Despite the air filters in the carburetor air cleaner and
crankcase ventilator, dust does work its way into the engine, and
this is particularly true when the car operates in dusty areas.
Changing oil flushes this dust out so that it cannot harm the engine.
Car manufacturers recommend that a car that has been driven
through a dust storm, for example, should have the oil changed immediately, regardless of how recently the last oil change was made.
At the same time, the air filter should be cleaned and the oil filter
(if used) changed. In addition to the changing of engine oil,
the lubrication of various pOints in the engine accessories and
[340]
\
\'\
Lubricating-system Service
§229
LUBRICANT-l'I lgh
O ... d. Mln.... 1 011 O.~
t.\l.l:...·l~ ..~\
..\.t...,'t'·HI.
0 .... u llbric... t) of SAl:
No. 90 Vlac:qa!tl' Or SAt:.
No. 40 E ngl". 011 lor
Both Summar and Win.
tar. 0 . . .. L ubricant.
Cont&1n[ng Any E"t,..ma
P r ••• u ... Ingredient ••
Such . . Lud. Sulphur,
or Chlorine Compou.nd •
. Mua ' Not B. UMd.
Drain and RefUl at
15.000 miles
U •• lOW p nmlum ty". an·
V;ne 011 (SA C lo.lOW p,..'
m;um type I • •lso •• tI.fae:lory),See Tu:t. P!-.tJ.mln • ..,.
Shop Manual co ••r lng Au Lomalic:: T ..a_ml..lon...
DRAIN and FLUSH
LUBRICANT-U ..
Stud.baku Hypold Lu.
brlcant or Any SAE No.
90 H"po l d LubFlcanl
(M" ltI.Purpo •• O •• r Lu·
brh:anll M anufactured
by • Rapulllbl. 0.1 Com.
pany. Do No l at Any
Tim. M."V....tou. Branda
of Kypo id L ubricanta.
Fl';. 12-3. Chassis of one model automobile from bottom, showing items requiring lubrication, type of lubricant to use, and frequency with which service is
required. (Studebaker-Packard Corporation)
[341]
Automotive Fuel, Lubricating, and Cooling Systems
§230
chassis is periodically necessary, as shown in the typical lubrication
chart in Fig. 12-3.
§230. Oil-pan service Some authorities recommend that the oil
pan be Bushed out thoroughly about once a year in order to remove
accumulated sludge and dirt. In addition, and for the same reason,
oil strainers should be cleaned and engine oil lines blown out
with compressed air. On the type of engine using a combination
splash and pressure-feed lubricating system (Fig. 11-15) the aiming
of the oil nozzles can be checked and adjusted if necessary. A
12-4. Aim of oil nozzles checked with special gauge and water nozzle.
(Chevrolet Motor Division of General Motors Corporation)
FIG .
speCial oil-pan target gauge is supplied by the engine manufacturer
to enable the mechanic to perform this job. Figure 12-4 illustrates
the use of such a gauge. Note that the gauge is in position and
that water is being applied to the main oil pipe. The oil pan should
be tipped at a 45-degree angle to prevent the water from covering
the oil nozzles. With the water turned on just enough to straighten
the water streams at the end of the nozzles, the water streams
should pass through the target holes in the gauge. If they do not, a
special oil-nozzle wrench should be used to straighten the nozzles.
1. Rem
~ ving
oil pan. Oil-pan removal varies somewhat on different 2 rs due to interference of various other parts. On many
[342J
.
\.
Lubricating-system Service
§230
cars, the steering idler or other steering linkage must be detached.
In such case, carefully note the manner in which the linkage is attached and also the number of shims (when used), so that the
linkage can be correctly reattached. In addition, certain other parts
may require removal. For example, on late-model Ford V-8 engines the exhaust crossover pipe, starting motor, and flywheel
housing cover must be removed. On earlier models it is necessary
to remove engine mounting bolts and to raise the front end of the
engine. On Plymouth engines the clutch-housing dust cover should
be removed to prevent damage to the oil-pan gaskets.
With the preliminaries out of the way, the drain plug should be
removed so that the oil can drain out. Then, attaching bolts or nuts
should be taken off so that the oil pan can be removed. To prevent
pan from dropping, steady it while the last two bolts are "heing
taken out. If the pan sticks, pry it loose with a screw drive.. but
proceed carefully to avoid distorting the pan. If the pan strikes the
crankshaft and will not come free, turn the engine crankshaft a
few degrees so that the counterweights move out of the way.
2. Cleaning oil pan. After removal, the oil pan should be cleaned
with cleaning solvent or with a steam cleaner. All traces of gasket
material and cement should be removed from the pan and engine
block. The oil screen should also be cleaned so that all trace of
sludge or dirt is removed.
Before replacing the oil pan, make sure that every
trace of solvent has been removed from the pan. Be sure the pan is
absolutely clean and dry. Even small amounts of solvent retained
in the oil pan may cause engine trouble later. Some types of solvent
have a damaging effect on engine parts in a running engine.
Caution:
3. Replacing oil pan. To replace the pan, apply gasket cement
to the gasket surfaces of the oil pan. Be sure gasket and pan bolt
holes align, and put gasket (or gaskets) into position. Lift oil pan
into place and temporarily attach it with two bolts, one on each
side. Then examine the gaskets to make sure that they are still in
position. Note that on the type of oil pan shown in Fig. 12-5 the
end gaskets appear to be somewhat too long so that their ends
project slightly beyond the mounting flange of the oil pan. These
ends should not be cut off, since they will crush down against the
block to provide a better seal. If the gaskets are all still in position,
[343]
Automotive Fuel, Lubricating, and Cooling Systems
§231
install the rest of the attaching bolts, and turn them up to the
proper tension. Install the oil plug, and add the correct amount
and grade of oil. Replace other parts that have been removed or
loosened. Check the oil-pan gaskets for leakage after the engine has
been run for a while and allowed to warm up.
FIG. 12-5. Oil pan with gaskets in place, ready for pan replacement. (Plymouth
Division of Chrysler Corporation )
§23 1. Relief valve Most relief valves are not adjustable, but a
change in oil pressure can be obtained by installing springs of
different tension. This is not usually recommended, however, since
a spring of the proper tension is originally installed on the engine,.
and any change of oil pressure is usually brought about by some
defect which requires correction. For example, badly worn bearings
may pass so much oil that the oil pump cannot deliver sufficient
oil to maintain normal pressure in the lines. Installing a stronger
spring in the relief valve will not increase oil pressure, since under
such conditions the relief valve is not operating anyway.
Oil filters are serviced by replacing the oil-filter
element or the complete filter, according to the type. Oil screenS
are serviced by Rushing out accumulated sludge and dirt. Where
the application is equipped with a floating type of oil intake, the
float and \screen should also be cleaned.
§232. Oil filters
[344}
\
1\
\
Lubricating-system Service
§234
As the oil filter becomes clogged, it passes less and less oil. Some
indication of the condition of the oil filter can be gotten by feeling
it after the engine has been operated for a short time. If the filter
is hot to the touch, it indicates that oil is flowing through the filter.
If it is cold, the probability is that the filter is clogged and is not
passing oil. An additional check can be made by disconnecting the
filter outlet with the engine running at low speed to see if oil is
flowing through the filter. However, rather than depend on some
such check as this to determine filter efficiency, the best procedure
is to replace the filter or filter element at periodical intervals. The
usual recommendation is to replace the filter element every 5,000
miles. More frequent replacement should be made if the car is
operated in unusually dusty conditions.
§233. Filter-element replacement To replace the filter element, remove drain plug (if present) from bottom of housing. Take cover
off by loosening center bolt or clamp. Lift out element. If filter
housing has no drain plug, remove old oil or sediment with a Siphon
gun. Wipe out inside of housing with clean cloth. Be sure no traces
of lint or dirt remain. Install new filter element. Replace plug and
cover, using a new gasket. Start engine, and check for leaks around
the cover. Note if oil pressure has changed (with a new element,
which passes oil more easily, it may be lower). Check level of oil
in crankcase, and add oil if necessary. Installing a new filter element
usually requires the addition of a quart of oil to bring oil level up
to proper height in crankcase.
NOTE: It is always best policy to change the oil whenever the oil
filter is changed. The new oil filter should start out with clean oil.
On the type of filter that does not have a replaceable element,
the complete filter is replaced. This is done by disconnecting the
oil lines to the old filter, dismounting the filter, and then installing
the new filter and connecting the oil lines to it.
After a filter element or filter is replaced, the mileage should be
marked on the doorjamb sticker and the filter housing. Then, after
5,000 miles (or the specified replacement mileage) the driver and
serviceman will know that it is time to replace the filter element
again.
§234. Oil pumps The oil pump is a relatively simple mechanism
and requires little service in normal operation. If the pump is
[345]
Autom otive Fuel, Lubricating, and Cooling Systems
§234
badly worn, it will not maintain oil pressure and should be removed
for repah' or replacement. The procedure of removal, repair, and
replacement varies on different cars. Typical procedures follow.
1. Chevrolet. To remove the oil pump, the oil pan must be
drained and removed (§230). Then the oil lines should be discon nected.
a. Disconnect at the block the line going to the block, and disconnect at the pump the line to the screen.
h. Take out the retaining-sleeve lock screw, and remove the oil
pump.
c. Detach hom the oil pump the line that was connected to the
block. Then remove cover-attaching screws, cover, and gears
(Fig. 12-6 ). Remove the oil-pump inlet screen.
Driven gear
c
(J)
a
.~
Driven shaft
$:__ ~:;
:-=r:':--___ t~
'I
Drive shaft w/geor
Gasket
Pump
cover
o
I
Valve
FIG . 12-6. Gear-type oil pump disassembled. (Chevrolet Motor Division of
General Motors Corporation )
d. Wash all parts in cleaning solvent, and dry thoroughly. If
gears, shaft, or bearing is worn, the complete pump should be
replaced.
e. To reassemble the pump, place the drive gear and shaft in
the pump body, and put the idler gear in place so that the
smooth side of the gear will be toward the cover.
f. Put the cover in place with a new gasket, and fasten with
screws. Mter tightening screws, make sure the shaft turns
freely.
'.g. Attach the oil line that goes to engine block, aligning it so
it can be readily attached to the block when the pump is replaced. Put pump into place with oil lines aligned. Make sure
the q.rive slot in the shaft aligns with the tang on the distributO{ ~ haft.
[346]
\
\
\.
Lubricating-system Service
§234
h. Put retaining-sleeve lock screw in place and tighten it securely, making sure the tapered end of the screw goes into the
hole in oil-pump body. Tighten lock nut securely.
i. Connect oil lines. Make sure oil lines fit, to prevent possibility
of one oil line drawing pump to one side. This might cause
the shaft to misalign and seize.
i. Replace oil pan and add oil (§230).
2. Plymouth. Before removing the oil pump, take off the ignition
distributor cap and turn the engine crankshaft until the distributor
INNER ROTO
FIG . 12-7. Measuring clearance between the lobes of rotors on rotor-type oil
pump. (Plymouth Division of Chrysler Corporation)
rotor is in the No.1 firing position. The oil pump should then be removed. It may be necessary to take off the two upper cap screws
from the cover so as to get sufficient clearance for removal of the
pump. With the pump off, the crankshaft and distributor shaft
should not be moved, since this would change the ignition timing.
a. To disassemble the oil pump, take off the cover, turn it upside
down, and rotate the shaft. The outer rotor will slip out; you
should catch it in your hand.
b. Then drive out the gear-attaching pin, press the shaft out of
the drive gear, and slide the shaft and inner rotor assembly
[347]
Automotive Fuel, Lubricating, and Cooling Systems
§234
from the pump body. Inspect all parts, and replace any part
that appears worn, cracked, or otherwise defective.
c. Clearances between the rotors, body, and cover should be
checked. First check the clearance between the high lobes
of the rotors as shown in Fig. 12-7. If the clearance is more
than 0.010 inch, both rotors should be replaced.
d. Use micrometer to check thickness of both rotors and diameter of the outer rotor. Thickness should not be less than 0.748
COUNTER-CLOCKWISE
1
OIL PUMP AND
DISTRIBUTOR
DRIVE GEAR
ATTACHING SCREW HOLES
12-8. Lining up slot in readiness for replacing oil pump on engine.
(Plymouth Division of Chrysler Corporation)
FIG.
inch nor diameter less than 2.245 inches. If less than this, excessive wear has taken place, and rotors should be replaced.
e. Replace rotors in pump body, and measure clearance between
rotors and a straightedge held across the pump body. This
clearance should be 0.004 inch or less. If more, replace the
pump body.
f. Push the outer rotor to one side, and check clearance between
the oWer rotor and pump body. If it is more than 0.008 inch,
the pump body should be replaced.
[348)
\
I \
,
\
Lubricating-system Service
§234
g. If the cover is not absolutely :Oat or is grooved or scratched,
it should be replaced.
h. On reassembly, slide the drive shaft and rotor assembly into
the pump body, and then press the drive gear on the shaft
until the end play of the shaft is between 0.003 and 0.0l0 inch.
The clearance should be measured between the end of the
drive gear and the pump body.
i. Install the gear pin, and peen over the ends. If the pinholes
do not line up to provide the proper shaft end play, it will be
necessary to drill a new pinhole through the gear and shaft
with a %2 drill. This hole should be drilled at right angles to
the old hole. With the gear attached, install the outer rotor
and cover, using a new gasket.
i. To replace the pump on the engine, first line up the slot in
the drive shaft with the two attaching-screw holes in the
pump flange. Then turn the drive gear one tooth in a counterclockwise direction as viewed from the shaft end (Fig. 12-8).
Next, slide the pump into position without further turning
the drive gear. Fasten it with attaching screws.
3. Ford. Figure 12-9 is a disassembled view of a late Ford-type
oil pump. The oil pump is removed, with the oil pan off (§230), by
removing the attaching screws. On some earlier models No.1 or
Nos. 1 and 3 main-bearing caps must also be removed before the
oil pump can be taken off.
a. About the only reason for disassembling the oil pump is to
replace worn bearings or, possibly, worn gears. Before disassembling the oil pump, check bearing wear by moving the
drive shaft from side to side. If the side movement is more
than about 0.0005 inch, new bearings should be installed.
h. To disassemble the pump, remove the strainer-assembly retaining screws, strainer, and gasket. Then remove the cover
plate and the pump driven gear. Drive out pin, remove the
upper driven gear, and slide the shaft and drive-gear assembly
from the housing. The pressure relief valve can be removed,
if necessary, by cutting the lock wire and taking out the plug,
gasket, spring, and valve.
c. On reassembly, coat moving parts with light engine oil, slide
the shaft and drive-gear assembly into the housing, and install
[349]
Automotive Fuel, Lubricating, and Cooling Systems
§234
the upper driven gear with the retaining pin. Rivet the end of
the pin over to hold gear in place. When a new shaft and
drive-gear assembly is installed, drill a pinhole in the shaft
with a No. 30 drill after positioning the gear to give 0.016-inch
Washer
l~
capsrew
t
Cover
Body
assembly
Reiainer spring - - \
FIC. 12-9. Disassembled view of oil pump used on V-8 engine. (Ford Motor
Company)
clearance. Then install the pump driven gear, cover-plate gasket, and plate. Install pressure relief valve, spring, gasket, and
plug. Lock plug with lock wire, and twist wire around the
housing extension. Install strainer gasket and strainer.
d. To ~stal
the pump, slide it into the cylinder block, making
SUl"f\ the upper driven gear meshes with the driving gear, and
[350]
)
1\
\
\
Lubricating-system Service
§236
install the pump retaining screw and lock washer. Tighten
screw to 12 to 15 Ib-ft (pound-feet) torque with a torque
wrench. Install oil pan and add oil.
§235. Oil-pressure indicators Oil-pressure indicators are discussed
in detail in §222. These units require very little in the way of service. Defects in either the dash unit or the engine unit usually require replacement of the defective unit. On the type of unit that
makes use of vibrating thermostatic blades, dirty contact points,
which may cause incorrect readings, may usually be cleaned by
pulling a strip of bond paper between them. Be sure that no particles of paper are left between the points. Never use emery cloth
to clean the points since particles of emery might embed and prevent normal indicator action. If the indicator is not functioning in
a normal manner, a new engine indicating unit may be temporarily
substituted for the old one in order to determine whether the fault
is in the engine unit or the dash unit.
§236. Cleaning valves and piston rings When valves and piston
rings have become so clogged with carbon and other accumulations
that they cease to operate properly, it may be necessary to
overhaul the engine. Use of a detergent type of engine oil (§211, 6)
is suggested as one means of reducing the rapidity with which the
accumulations form. Also, regular oil changes will tend to remove
the impurities held in suspension in the oil before they have a
chance to settle on engine parts. Some authorities suggest the introduction of special compounds into the engine oil and through the
intake manifold as an aid in freeing sticking valves and rings.
Where engine trouble is experienced as a result of carbon accumulations on valves and rings, and where these parts are not excessively worn or damaged, improved engine performance can often
be obtained by the use of such compounds without engine overhaul.
For information on servicing of valves and piston rings, see Auto-
motive Engines.
CHAPTER CHECKUP
NOTE: Since the following is a chapter review test, you should review
the chapter before taking the test.
The chapter you have just completed has a number of important facts
in it that you will want to remember, since they will help you when you
go into the automotive service shop. In order to help you remember these
[351]
Automotive Fuel, Lubricating, and Cooling Systems
essential facts, the following checkup has been included. You can test
your memory and find out whether you are remembering those facts. At
the same time, you will be reviewing the chapter and thereby fixing the
important points more firmly in your mind. Write down the answers,
since this will help you remember.
Completing the Sentences
The sentences below are incomplete. After each sentence there are
several words or phrases, only one of which will correctly complete the
sentence. Write each sentence down in your notebook, selecting the
proper word or phrase to complete it correctly.
1. Oil is lost from the engine in three ways, by passing as a mist through
the crankcase ventilator, by leaking in liquid form, and by
evaporating
burning in the combustion chambers
condensing
2. Oil can enter the combustion chambers in three ways, through a
cracked vacuum-pump diaphragm, around the valve stems, and
past the float-bowl needle
past the manifold gaskets
past the piston rings
3. Water sludge forms more rapidly in engine oil with
high-speed
driving
slow-speed driving
short-trip driving
4. Oil-filter elements, according to usual recommendations, should be
replaced every
1,000
2,000
5,000
10,000
miles
5. Engine oil should be changed, according to usual recommendations
for average service, every
100
1,000
10,000
miles
Service Procedures
In the following, you should write down in your notebook the information called for. Do not copy the procedures from the book, but try to
write them in your own words. Give a step-by-step account of how to
do the service jobs asked for. This will help you remember the procedures later when you go into the automotive shop. Try to get hold of
various automobile shop manuals, and study them to learn how the
various servicing procedures are accomplished. Write up these procedures in your notebook, instead of following the book. This will
broaden your general knowledge of the car.
1. Explain how to use the pressure-bearing oil-leak detector.
2. Descril~
the three ways in which oil is lost from the engine.
3. Describe the three ways in which oil can enter the combustion
cham~rs.
[352}
..
Lubricating-system Service
4. What can produce low oil pressure? Why is this often considered a
danger signal?
5. What can produce excessive oil pressure?
6. Under what conditions is it wise to change oil more frequently than
usual?
7. Explain how to remove, clean, and replace an oil pan on a specific
model car.
B. Explain how to check an oil filter to see if it is operating.
9. Explain how to remove and replace an oil pump on a specific model
car.
10. Explain how to disassemble, check, and reassemble an oil pump
taken from a specific model car.
SUGGESTIONS FOR FURTHER STUDY
Watch the lubrication men at service stations as they change engine
oil and lubricate cars, to learn more about how these jobs are done.
Notice that they refer to charts that indicate the points of lubrication on
the cars they work on and also show the type and amount of grease or
oil to use. Study these charts to get a better idea of these important
points. In the automotive shop, notice how oil pans are removed from
various cars, and how oil pumps are repaired. Write down in your notebook any important facts you learn, so that you will be sure to remember
them.
[353}
13: Engine cooling system
THIS CHAPTER discusses the construction and operation of automotive-engine cooling systems. The cooling system is an integral
part of the engine, and the operation of one depends on the operation of the other. The cooling system will not operate unless the
engine is running; the engine will not operate (for very long) if
the cooling system is inoperative. Another book in the McGrawHill Automotive Mechanics Series (Automotive Engines) discusses
engines in detail and describes the relation of the engine and its
cooling system.
§237. Purpose of engine cooling system The purpose of the cooling
system is to keep the engine at its most efficient operating temperature at all engine speeds and all driving conditions. During the
combustion of the air-fuel mixture in the engine cylinders, temperatures as high as 4500°F may be reached by the burning gases.
Some of this heat is absorbed by the cylinder walls, cylinder head,
and pistons. They, in turn, must be provided with some means of
cooling, so that their temperatures will not reach excessive values.
Cylinder-wall temperature must not increase beyond about 400 or
500°F. Temperatures higher than this will cause the lubricatingoil film to break down and lose its lubricating properties. But it is
desirable to operate the engine at temperatures as close to the limits
imposed by oil properties as pOSSible. Removing too much heat
through the cylinder walls and head would lower engine thermal
efficiency (or heat efficiency-see Automotive Engines). Cooling
systems are designed to remove 30 to 35 percent of the heat produced in the combustion chambers by the burning of the air-fuel
mixture.
Since the engine is quite inefficient when cold, the cooling system
includes deyices that prevent normal cooling action during engine
1354]
Engine Cooling System
§238
warm-up. These devices allow the working parts to reach operating
temperatures more quickly and shorten the inefficient cold-operating time. Then, when the engine reaches operating temperatures,
the cooling system begins to function. Thus, the cooling system
cools rapidly when the engine is hot, and it cools slowly or not at
all when the engine is warming up or cold.
Two general types of cooling system are used, air cooling and
liquid cooling. Automotive engines now employ liquid cooling, although some special engines for airplanes, motorcycles, and so
forth, are air-cooled.
§238. Air-cooled engines In air-cooled engines the cylinders are
usually semi-independent and not grouped in a block. They are
so placed that an adequate volume of air can circulate around each
cylinder, absorbing heat in passing. Radial aircraft engines, in
FIG. 13-1. Air-cooled airplane engine. Passage of air around cylinders removes
heat from cylinders.
[355]
§239
Automotive Fuel, Lubricating and Cooling Systems
which the cylinders are placed in a circle around a common center,
represent this design (Fig. 13-1). Each cylinder normally has a series of ribs or fins, so that the cooling area is considerably increased.
§239. Liquid-cooled engines In liquid-cooled engines, a liquid is
circulated arotmd the cylinders to absorb heat from the cylinder
walls. The liquid is usually water, to which antifreeze solution is
added during cold weather. The heated water is then conducted
through a radiator in which the heat in the water is passed on to
air that is Howing through the radiator. The water passages, size
JIoIIIII..
13-2. Simplified diagram of water cooling system of thermosiphon type.
A, cylinders; B, waterjackets; C, return hose ; D, upper hose; E , radiator;
F , upper tank.
FIG .
of radiator, and other details are so designed as to maintain the
cylinder walls, head, pistons, and other working parts at efficient,
but not excessive, temperatures. Two types of liquid-cooling systems have been used, natural circulation ( thermosiphon ) and
forced circulation.
1. Thermosiphon cooling. Thermosiphon, or natural-circulation,
liquid-cooling systems are no longer widely used. This type of system depends upon the expansion of heated water for the motive
power that causes the water to circulate (Fig. 13-2). The water
around the cylinders is heated and consequently expands so that
the weight of a given volume is decreased. Since it is lighter, it rises
and is displa~e
by the cooler and heavier water from the radiator.
[356]
\
Engine Cooling System
§239
The warm water enters the top of the radiator and begins to lose
heat to the radiator. As it cools it contracts and becomes heavier,
so that it sinks to the bottom of the radiator, continuing to lose
heat as it does so. The pressme that it exerts through the return
line to the cylinders causes the warmer water around the cylinders
to rise. This provides constant circulation of the liquid between
the cylinders and the radiator. The hotter the engine, the more
13-3. Cooling system of a V-8 engine. Engine is partly cut away to show,
by arrows, the circulation of water. The radiator is not shown. See §243 for a
discussion of radiators. ( Mercury Division of Ford Motor Company)
FIG.
rapidly the water circulates. The system thus tends to maintain
fairly constant cylinder-wall temperatmes. The disadvantage of the
system is that circulation is seriously reduced by any accumulation
of scale or foreign matter in the passages and lines, and this in
tmn causes overheating of the engine.
2. Forced Circulation. In the forced-circulation system a water
pump (§241 ) is incorporated (Figs. 13-3 and 13-4) to assme continued and rapid circulation of the cooling liquid.
[357]
§240
Automotive Fuel, Lubricating, and Cooling Systems
§240. Water jackets Just as we might put on a sweater or a jacket
to keep warm on a cool day, so are water jackets placed around the
engine cylinders. There is this difference: water jackets are designed to keep the cylinders cool. Early engines with separately
cast cylinders used sheet metal jackets that were attached to the
FIG. 13-4. Cooling system used in overhead-valve engine. (Chevrolet Motor
Division of General Motors Corporation )
cylinders after the cylinders had been completed and assembled
to the engine block. This expensive construction was done away
with as the casting of intricate cylinder blocks was perfected. In
such cylinder blocks the water jackets are cored out (see Automotive Engines book) so that water can circulate freely around the
cylinders as well as around the valve openings (Figs. 13-3 and
13-4).
\
On many engines water-distributing tubes are used to direct the
[358J
\
\
\
Engine Cooling System
§240
FIG. 13-5. Use of water-distributing tube to cool valves. (Pontiac Motor Division of General Motors Corporation)
FIG. 13-6. Water-distributing tube (1) being pulled by hook (2) from cylinder
block. This tube, similar to the one shown in Fig. 13-5, has holes properly
spaced to provide adequate cooling of valve seats. (Plymouth Division of
Chrysler Corporation)
[359]
Automotive Fuel, Lubricating, and Cooling Systems
§241
How of the cooling water as it enters the water jackets from the
radiator. Valve seats and guides must be kept within a safe temperature range, and, by directing a flow of cooling water at them
through distributing tubes and nozzles, they are adequately cooled
(Figs. 13-5 and 13-6).
Fan-pulley
hub
~
I~O
Seof.ports
Shoff and
bearing
Gasket
13-7. Disassembled view of water
pump. (Pontiac Motor Division of
General Motors Corporation)
FIG.
13-8. Sectional view of water
pump showing manner of supporting
shaft on double-row ball bearing and
method of mounting fan and pulley
on shaft. (Studebaker-Packard CorpOTation)
FIG.
§241. Water pumps Water pumps are usually of the impeller type
and are mounted at the front end of the cylinder block between the
block and the radiator (Fig. 13-3). The pump (Figs. 13-7 to 13-10)
consists of fl housing, with a water inlet and outlet, and an impeller.
The impel~r
is a flat plate mounted on the pump shaft with a series
[360]
\,
Engine Cooling System
§242
of flat or curved blades, or vanes. \Vhen the impeller rotates, the
water between the blades is thrown outward by centrifugal force
and is forced through the pump outlet and into the cylinder block.
The pump inlet is connected by a hose to the bottom of the radiator,
and water from the radiator is drawn into the pump to replace the
water forced through the outlet.
The impeller shaft is supported on one or more bearings; a seal
prevents water from leaking out around the bearing. The pump is
PlUNGO
(OPf IMlING p.oo)
L THE fAN IS NEEDED ONLY AT SLOW CAP. sPffP5
OR UNDER ASNORMAl CON omONS
• 2. TH£II!E IS NO PEtKI:Pll8l i fA'" NOlSi SHOw
\300 fl..N Q V III.
3 fAN
~,fi'
M REOU!RfMENlS M.VU ,,<Ill l:H)
1!J()()
4. AuTOMATIC FAN SAV~
UP to 17 8; H P AT 3800
ENGINE' It~M.
aO.1S M.P.H In II;ICKDOWNI
UHOtR l'lORMAl CONOti\ONS.
.-
-
FIC. 13-9. Automatic engine fan with thermostat to conb-oI its speed. Fan
turns no faster than is necessary to keep engine from overheating. (Mercury
Division of Ford Motor Company)
driven by a belt to the drive pulley, which is attached to the front
end of the engine crankshaft (Fig. 1-1).
§241. Engine fan The engine fan usually mounts on the waterpump shaft and is driven by the same belt that drives the pump
and the generator (Fig. 13-8). The purpose of the fan is to provide
a powerful draft of air through the radiator to improve engine cooling. The fan usually has from two to six blades, which in rotating
pull air through the radiator. Some applications are equipped with
a fan shroud that improves fan performance. The shroud increases
the efficiency of the fan, since it assures that all air pulled back
by the fan must first pass through the radiator.
[361]
Automotive Fuel, Lubricating, and Cooling Systems
§242
fLATS FOR
WASHER
13-10. Disassembled view of water pump used in a V-8 engine. (De Soto
Division of Chrysler Corporation)
FIG.
V BELT
ULLEY
Shell
attaching
baits
Lower
Water outlet
13-11. V belt in
pulley groove.
FIG.
\.
\.
\
[362]
\.
FIG.
13-12. Radiator assembly.
Engine Cooling System
§242
Some engines are equipped with an automatic engine fan that
will not exceed a predetermined speed or that will rotate only as
fast as is required to keep the engine from overheating. Several
types of control are used, including centrifugal and thermostatic. A
thermostatically controlled automatic fan is shown in Fig. 13-9. The
thennostatic capsule in the fan is subjected to the cooling-water
temperature. As the water temperature increases, the thermostat
mIter passage
Wafer passoge
Tube
Woter passoge
Fin
Tube and helical fin ar
tube and individual fin core
Air tube cellular
Tube and plate fin core
core
Tube and corrugated fin core
Ribban cellular
core
FIG. 13-13. Types of radiator cores.
expands, moving the operating rod toward the fan. This action imposes additional pressure on the clutch disks in the fan hub so that
the fan turns faster. When the cooling-water temperature drops, the
thermostat contracts, less pressure is exerted on the clutch disks,
and the fan turns slower. In the unit shown, the maximum fan speed
is about 2,600 rpm. Since the fan will not turn faster than this, even
though the fan pulley may be tmning much faster, considerable
power is saved. In fact, the unit shown is said to save as much as 17
brake horsepower at 3,800 engine rpm. Furthermore, since the fan
never tmns at very high speed, fan noise is kept to a minimum.
[363J
Automotive Fuel, LubricaUng, and Cooling Syste17u
§243
Most fan belts are V type (Fig. 13-11). Friction between th(
sides of the belt and the sides of the grooves in the pulley:
causes the driving power to be transmitted through the belt fron
one pulley to the other. The V-type belt provides a substantial are~
of contact, so that considerable power may be transmitted; th(
wedging action of the belt as it curves into the pulley grooves aid:
in preventing belt slippage. Figure 1-1 shows a V belt in place 01
the generator, engine fan, and crankshaft pulley of an engine.
§243. Radiator The radiator (Fig. 13-12) is a device for holding:
large volume of water in close contact with a large volume of air s(
FIG. 13-14. Construction of tube-and-fin radiator core.
that heat will transfer from the water to the air. The radiator carl
is divided into two separate and intricate compartments; wate
passes through one and air passes through the other. Radiator core
are of nve basic types (Fig. 13-13). Two of the more commonl:
used type!' for passenger cars are the tube-and-nn (Fig. 13-14) anI
the ribbon-cellular (Fig. 13-15). The tube-and-nn type consists 0
a series of tubes extending from the top to the bottom of the radia
tor (or from upper to lower tank). Fins are placed around the tube.
to impro e heat transfer. Air passes around the outside of the tubes
betweeu the nns, absorbing heat from the water in passing.
The ~\bon-celuar
radiator core (Fig. 13-15) is made up of :
.[364]
\
\
\
Engine Cooling System
§244
large number of narrow water passages formed by pairs of thin
metal ribbons soldered together along their edges, running from
the upper to the lower tank The edges of the water passages,
which are soldered together, form the front and back surfaces of the
radiator core. The water passages are separated by air fins of metal
ribbon, which prOVide air passages between the water passages.
Air moves through these passages from front to back, absorbing
heat from the fins. The fins, in turn, absorb heat from the water
moving downward tlu-ough the water passages. As a consequence,
the water is cooled.
Wufer fu/J6S
Top
,'---header
Air fins
,,
Water
- - tube
,
/
FIG. 13-15. Construction of ribbon-cellular radiator core.
On every radiator a water chamber, or tank, is provided at the top
of the radiator, into which hot water is delivered from the engine.
A filler cap placed on the water chamber can be removed in order
to add water to replace that lost by evaporation or leakage.
Radiator grills, which add to the streamlined appearance of the
car, place some added load on cooling systems, since they tend to
restrict the flow of air through the radiator. However, where they
are used, the cooling system is deSigned to meet all cooling requirements adequately.
§244. Hot-water car heater Many automobiles are equipped with
car heaters of the hot-water type (Fig. 13-16). This device might
[365]
Automotive Fuel, LubricaUng, and Cooling Systems
§243
Most fan belts are V type (Fig. 13-11). Friction between the
sides of the belt and the sides of the grooves in the pulleys
causes the driving power to be transmitted through the belt from
one pulley to the other. The V-type belt provides a substantial area
of contact, so that considerable power may be transmitted; the
wedging action of the belt as it curves into the pulley grooves aids
in preventing belt slippage. Figure 1-1 shows a V belt in place on
the generator, engine fan, and crankshaft pulley of an engine.
§243. Radiator The radiator (Fig. 13-12) is a device for holding a
large volume of water in close contact with a large volume of air so
FIG. 13-14. Construction of tube-and-fin radiator core.
that heat will transfer from the water to the air. The radiator core
is divided into two separate and intricate compartments; water
passes through one and air passes through the other. Radiator cores
are of five basic types (Fig. 13-13). Two of the more commonly
for passenger cars are the tube-and-fin (Fig. 13-14) and
used type~
the ribbon-cellular (Fig. 13-15). The tube-and-fin type consists of
a series of tubes extending from the top to the bottom of the radiator (Qr from upper to lower tank). Fins are placed around the tubes
to impro e heat transfer. Air passes around the outside of the tubes,
betweel;l. the fins, absorbing heat from the water in passing.
The ~\ bon-celuar
radiator core (Fig. 13-15 ) is made up of a
J364]
\
\
\
Engine Cooling System
§245
stamped "170" should start to open at 166 to 174°F and be fully
opened at 194°F. Thermostats of the proper characteristics are
selected to suit the operating requirements of engines on which
they are used.
FIG. 13-17. Thermostat, used to restrict water circulation with engine cold,
shown in place in cylinder head. (Plymouth Division of Chrysler Corporation )
3. Thermostat openings
5. Thermostat
1. Elbow
2. Gasket
4. Gasket
6. Gasket
With the engine cold and the thermostatic valve consequently
closed, the water pump circulates the water as shown in Fig.
13-19. The water is merely recirculated through the cylinder block
and head. A small spring-loaded bypass valve is forced open by the
water pressure from the pump so that the water can circulate a~
shown by the arrows. Restriction of water circulation in this mane
~
prevents the removal of any appreciable amount of heat from the
engine by the cooling system, and the engine consequently reaches
operating temperatures more rapidly. When the engine reaches
operating temperature, the thermostatic valve beginS to open, and
water can then circulate through the radiator as shown in Fig.
13-20. Figure 13-18 shows the water circulation through the ther[367]
246
Autornotive Fuel, Lubricating, and Cooling Systems
nos tat when the thermostat is open. Operation of the cooling sys.e m then proceeds in a normal manner as already described.
Instead of the spring-loaded-valve type of bypass for water re:!irculation with the thermostatic valve closed, shown in Fig. 13-19,
FIG. 13-18. Thermostat in place in cylinder head, showing water circulation
through thermostat when thermostat is opened. (Studebaker-Packard Corporation)
some engines use a small bypass passage from the cylinder head
through the engine block to the pump inlet.
To improve cooling efficiency and
prevent evaporation and surge losses, many late automobiles use a
pressure cap on the radiator (Figs. 13-21 and 13-22). At sea level,
where atmospheric pressure is about 15 psi (pounds per square
inch), water boils at 212°F. At higher altitudes, where atmospheric
pressure is less (§34), water will boil at lower temperatures. Higher
pressures increase the temperature required to boil water. Each
added pound per squru.'e inch inCl'eases the bOiling point of water
about 3 ~ OF. The us~
'of a pressure cap on the radiator increases
the air pressure with~
the cooling system several pounds per square
§246. Radiator pressure cap
[
]
/\
\.
Engine Cooling System
§246
inch, so that the water may be circulated at higher temperatUI'
without boiling. The water thus enters the radiator at a higher te;_~
perature, and the difference in temperature between the air and the
water is greater. Heat then is more quickly transferred from the
FIG. 13-19. Location of thermostat in
water passage between cylinder head
and radiator. Engine is cold, thermostat closed, and bypass valve open.
Water circulates as shown by arrows.
(Buick Motor Division of General
Motors Corporation)
FIG. 13-20. Circulation of water with
thermostat open. Some systems incorporate a bypass valve as shown here
and in Fig. 13-19. Other systems use
a bypass port. (Buick Motor Division
of General Motors Corporation)
water to the air, improving cooling efficiency. Evaporation of water
is reduced by the higher pressure, inasmuch as the bOiling point of
the water is higher. The pressure cap also prevents loss of water due
to surging when the car is quickly braked to a stop.
The pressure cap fits over the radiator filler tube and seals tightly
around the edges. The cap contains two valves, the blowoff valve
and the vacuum valve. The blowoff valve consists of a valve held
against a valve seat by a calibrated spring. The spring holds the
[369]
§246
Automotive Fuel, Lubricating, and Cooling Systems
valve closed so that pressure is produced in the cooling system. If
pressure is obtained above that for which the system is designed,
the blowoff valve is raised off its seat, relieving the excessive pressure. Pressure caps are designed to provide as much as 12 pounds
of pressure per square inch in the cooling system; this increases the
boiling point of the water to as much as 250°F.
FIG. 13-21. Radiator pressure cap.
(AC Spark Plug Division of General Motors C01poration)
FIG. 13-22. Cutaway view of radiator pressure cap showing pressure
seal valve and vacuum seal valve.
The vacuum valve is designed to prevent the formation of a
vacuum in the cooling system when the engine has been shut off
and begins to cool. If a vacuum forms, atmospheric pressure from
the outside Cfluses the small vacuum valve to open, admitting air
into the raqiator. Without a vacuum valve the pressure within the
drop so low that atmospheric pressure would colradiator mi~t
I.
lapse it.
,
\
[3701
'.
Engine Cooling System
§247
Antifreeze solutions are required tc
prevent freezing of the water when temperatures drop below 320F.
When water freezes in the engine, the resulting expanding force is
often sufficient to crack the cylinder block and the radiator. Antifreeze solutions added to and mixed with the water prevent freezing
of the mixture. A good antifreeze material must mix readily with
water, prevent freezing of the mixture at the lowest temperatures
encountered, and circulate freely; it must not damage the cooling
system by corrosive action or lose its antifreezing properties after
§247. Antifreeze solutions
ANTI-FREEZE SOLUTIONS
PROTECTING TO -20°F
"ETHYLENE
GLYCOL"
WATER
FREEZES AT +32°P
ALCOHOL BASE
ANTI-FREEZE
FIG. 13-23. Comparison of boiling points of water and antifreeze solutions.
extended use. In the past a number of different materials have been
tried, including salt and sugar solutions, oil, kerosene, and glycerin,
but their use has been generally abandoned because of harmful
or dangerous effects. The most commonly used antifreeze materials
are now either alcohol or alcohol-base, or ethylene glycol. The
alcohol-base materials make only temporary antifreeze solutions,
since they evaporate at temperatures below the boiling point of
water and thus are gradually lost (Fig. 13-23). Such materials may
require periodic additions to maintain an antifreeze solution of
adequate strength. The ethylene glycol antifreeze materials are of
the so-called "permanent" type, since they remain liquid at the
boiling point of water.
[371]
§248
Automotive Fuel, Lubricating, and Cooling Systems
Antifreeze materials are mixed with water in various proportions
according to the expected temperature. The lower the temperature,
the higher the percentage of antifreeze material in the solution
necessary to prevent freezing of the mixture. Figure 14-7 illustrates
a hydrometer used to measure the strength of the antifreeze solution.
§248. Temperature indicators In order that the operator will know
at all times the water temperature in the cooling system, a temperature indicator is installed in the car. An abnormal heat rise is a
3
I . BEZEL
2. GASKET
3. GLASS
4. REflECTOR RING
5. MECHANI SM \CASE
AND CAPILLARY
FIG. 13-24. Vapor-pressure temperature indicator. (AC Spark Plug Division of
General Motors Corporation)
warning of abnormal conditions in the engine; the indicator permits
the operator to stop the engine before serious damage is done.
Temperature indicators are of two general types, vapor pressure
and electric.
1. Vapor Pressure. The vapor-pressure temperature indicator
(Fig. 13-24) consists of an indicator bulb and a tube connecting the
bulb to the indicator unit. The indicator unit contains a curved or
Bourdon tube, one end of which is linked to the indicator needle.
The other end is open and is connected through a tube to the bulb.
The indicator bulb, usually placed in the water jacket of the engine,
is filled with a liquid that evaporates at fairly low temperature. As
the engine temperature increases, the liquid in the bulb begins to
evapor
~, creating pressure that is conveyed through the connect,1372]
\,
Engine Cooling System
§248
ing tube to the Bourbon tube in the indicating unit. The pressure
tends to straighten out the tube; the resulting movement causes the
indicating needle to move across the dial face and indicate the
temperature in the water jacket. This unit is much like the oilpressure indicator illustrated in Fig. 11-29.
2. Electric indicators. Electrically operated temperature indicators are of two types, the balancing-coil type and the bimetal-thermostat type. The balancingcoil type oil-pressure indicator
( §222 ), fuel gauge (§38), and
POINTER
ENGINE UNIT IS
temperature indicator all operIMMERSED IN
ENGINE COOLANT.
ate in a similar manner. The
RESISTANCE OF
UNIT DECREASES
dash indicating units are, in fact,
WITH HEAT
practically identical, consisting
of two coils and an armature to
BATTERY
which a needle is attached (Fig. ~I
13-25). The engine unit changes
IGNITION -== DASH UNIT
SWITCH
resistance with temperature in
FIG. 13-25. Circuit diagram of elecsuch a way that at higher tem- tric-resistance temperature-indicator
peratures it has less resistance system.
and will thus pass more current.
When this happens, more current passes through the right-hand
coil in the indicating unit, so that the armature to which the needle
is attached is attracted by the increased magnetic field. The
armature and the needle move around so the needle indicates a
higher temperature.
The bimetal-thermostat type of temperature indicator is similar to
the bimetal-thermostat fuel gauge (§38). The dash units are practically identical. The engine unit of the temperature indicator,
while slightly different in appearance from the tank unit of the
fuel gauge, operates in a somewhat similar manner. In the temperature indicator the temperature of the cooling liquid is directly imposed on the engine-unit thermostatic blade. When the temperature is low, most of the blade heating must come from electric
current. More current flows, and the dash-unit distorts a considerable amount to indicate a low temperature. As temperature increases, less heat from current flow is required to bring the engineunit blade up to operating temperature. Less current flows, and the
dash unit indicates a higher temperature.
[373]
Automotive Fuel, Lubricating, and Cooling Systems
CHAPTER CHECKUP
NOTE: Since the following is a chapter review test, you should review
the chapter before taking the test.
The cooling system is, of course, essential to the operation of the
automotive engine. If it fails to operate properly, the engine will not
operate properly; engine failure may result. It is thus important for you
to understand how the cooling system operates and how the different
component parts that make up the cooling system function. In order to
help you remember these essential facts, the following checkup has
been included. You can test your memory and find out if you are remembering those facts. At the same time, you will be reviewing the
chapter and thereby fixing the important pOints more firmly in your mind.
Write down the answers, since this will help you to remember.
Completing the Sentences
The sentences below are incomplete. After each sentence there are
several words or phrases, only one of which will correctly complete the
sentence. \Vrite each sentence down in your notebook, selecting the
proper word or phrase to complete it correctly.
1. The cooling system removes from the engine
30 to 35
50
to 60
85 to 90
percent of the heat produced in the combustion chambers.
2. Included in the forced-circulation system, to assure rapid water
circulation, is a
thermostat
distributing tube
water
pump
3. Surrounding each cylinder, to assure effective cooling, are water
radiators
tubes
jackets
4. Water pumps used in engine cooling systems are usually of the
expeller
repeller
impeller
compeller
type.
5. Engine fan belts are usually of the
flat
C
D
V
type.
tube-and-fin and ribbon6. Radiators are of two general types,
distributing-tube and
cellular
cylindrical and thermostatic
hose
7. The cooling-system thermostat contains a valve that
opens
closes
with increasing temperature.
S. The radiator pressure cap has two valves,
intake and vacuum
exhaust and thermostatic
blowofJ (Ind vacuum
[374J
\
,
\
\
\
\
Engine Cooling System
9. One widely used permanent antifreeze is
ethylene glycol
kerosene
glycerin
10. Two types of temperature indicators are
static
vapor pressure and electric
temperature
ethyl gas
electric and thermovapor pressure and
Definitions
In the following, you are asked to write down certain definitions of important terms, purposes of cooling-system components, and so on. The
act of writing down these answers in your notebook will help you remember them. It will also make your notebook a more valuable reference
for you; you can quickly look up important facts about the automobile
that you want to recall.
1. What is the purpose of the cooling system?
2. Why is the thermosiphon cooling system no longer Widely used?
3. Where are water jackets located in the engine, and what is their
purpose?
4. What is the purpose of the water-distributing tube?
5. Describe the construction and operation of a typical water pump.
6. What is the purpose of the radiator?
7. Describe the construction and operation of the cooling-system
thermostat.
8. Describe the construction and operation of the cooling-system radia
tor pressure cap.
9. What is the purpose of adding antifreeze to the cooling system?
10. Describe the construction and operation of the vapor-pressure type
of temperature indicator; the balancing-coil type; the bimetal-therm(l·
stat type.
SUGGESTIONS FOR FURTHER STUDY
Examine different engines, radiators, thermostats, and water pumps so
that you get a better idea of how the water is circulated in the cooling
system. Study the illustrations and descriptions of cooling systems in all
the car shop manuals you can find. Study Automotive Engines (another
book in the McGrawHill Automotive Mechanics Series) for further
information on engine thermal efficiency and heat losses. Heat is removed
from the engine in several ways; the cooling system is responsible for
removing only part of it. You will find further information on this subject
in Automotive Engines. Be sure to write down any important facts you
run across that you want to remember. Write them down in your notebook.
[375]
14: Cooling-system service
THIS CHAPTER describes the testing, care, servicing, and repair
of automotive-engine cooling systems.
Over a period of time, rust and scale
accumulate in the radiator and engine water jackets; the rust and
scale restrict the circulation of water, and the engine tends to overheat (Fig. l4-1). In addition, the hose and connections between the
§249. Cooling-system tests
FIG. 14-1. Accumulation of rust and scale in engine water jackets. (Chevrolet
Motor Division of General Motors Corporation)
radiator and the engine may deteriorate, causing leakage or inadequate passage of water. The thermostat, if stuck or distorted,
may not ~ ldse
and open properly and will thus reduce the effective[376]
\.
Cooling-system Service
§249
ness of the cooling system. A number of tests of the cooling system
and its components can be made to determine the condition of
these parts. In addition, the strength of the antifreeze solution can
be tested.
1. Testing thermostat. The action of the thermostat can be observed by placing it in a pan of water and heating the pan. A thermometer should be suspended in the water, so that the temperature
at which the thermostat starts to open, as well as the full-open
temperature, can be determined. The thermostat should not be
placed on the bottom of the pan
but suspended by a wire or placed
on a screen an inch or so above
the bottom (see Fig. 14-2). Thermostats are calibrated to operate
at various temperatures. If a thermostat does not function according to specifications, it should be
replaced.
2. Testing system for rust and
scale. The appearance of the
water is some indication of
whether rust and scale have accumulated in the cooling system.
If the water is rusty or muddy in FIG. 14-2. Testing cooling-system
thermostat.
appearance, rust is present. A
fairly accurate measurement of the am01mt of rust and scale
present can be made if the capacity of the cooling system is known.
All water should be drained and fresh water measured and added
until the system is filled. Comparison of the amount of added water
with the specified capacity of the system proyides an indication
of the amount of rust and scale present.
S. Testing radiatm' for restriction. If the radiator hose connections are removed, the radiator drained, and a stream of water from
an ordinary garden hose introduced into the top of the radiator, the
water should run through the radiator and out without filling up
the radiator. If the water runs out slowly, the radiator is clogged.
Another test for restrictions in the radiator is to start the engine,
allow it to warm up, and then turn the engine off and feel the
radiator with the hand. It should be hot at the top and warm at the
[377]
Automotive Fuel, Lu,bricating, and Cooling Systems
§249
bottom, with an even temperature increase from bottom to top.
Cold spots indicate clogged sections.
Caution: Be sure the engine is tmned off. More than one person
has injmed his hand seriously by placing it too near an engine fan
when the engine was running.
4. Examining hose and hose connections. The appearance of the
hose and connections will usually indicate their condition. If the
hose is rotted and soft and collapses easily when squeezed, it should
be replaced. Figme 14-3 illustrates a badly deteriorated section of
hose that has been split open to show the internal appearance.
FIG.
14-3. Water hose that has become defective. (Federal-Mogul Corporation)
5. Testing water pump. There is no accurate way to test the
action of the water pump on the car. However, some idea as to its
operating condition may be obtained by squeezing the upper hose
connection in the hand, with the engine warm and running. If
pressure can be felt as the engine is speeded up, it is an indication
that the water pump is operating in a normal manner.
6. Testing for air suction into system. If leaks exist at any point
between the radiator and the water pump, air will be drawn into
the system as shown in Fig. 14-4. Air bubbles will cause foaming
and loss of the cooling water. The water could, of course, be replaced, but if antifreeze is also lost, then replacement is an expense.
There is also the danger of losing antifreeze protection in this way.
speeds up corrosion and rust. To check for air
Au' in the ~y stem
suction, £11 the radiator, attach a hose from the overflow pipe, and
[378]
\
"
\
\,
§249
Cooling-system Service
put the lower end of the hose into a container of water, as shown
(Fig. 14-4). Start the engine and run it until it is warmed up. If
bubbles appear in the container of water, then air is being sucked
into the cooling system. (It might be exhaust-gas leakage, as noted
in the following paragraph.) Repair by tightening or replacing
hose and hose clamps. If this does not cure the trouble, then either
14-4. Testing for air suction into cooling system. Arrows indicate paints
at which air might enter.
FIG.
there is exhaust-gas leakage or the water pump is leaking. Check
the system as noted in the following paragraph. If no exhaust-gas
leakage is found, then the trouble is probably in the pump, and it
should be repaired (§254).
7. Testing for exhaust-gas leakage. A defective cylinder-head
gasket may allow exhaust gas to leak into the cooling system. This
is very damaging, since strong acids will form as the gas unites
with the water in the cooling system. These acids corrode the
radiator and other parts in the cooling system. A test for exhaust-gas
(379)
Automotive Fuel, Lubricating and Cooling Systems
§249
leakage may be made by disconnecting the upper hose, removing
the thermostat and the fan belt, and draining the system until the
water level stands just above the top of the cylinder head (Fig.
14-5). The engine should be started and accelerated quickly several
FIG. 14-5. Testing for exhaust-gas leakage into system.
times. If the water level rises appreciably, or if bubbles appear,
exhaust gas is leaking into the cooling system. A new gasket should
be installed and the cylinder-head bolts properly tightened.
8. Testing fan belt. Fan-belt adjustment should be checked by
pressing in on the belt (engine not running) halfway between the
generator pulley and fan pulley, as shown, for example, in Fig. 14-6.
The amount of deflection that the belt will undergo varies with different makes of car. Belt tension is adjusted by loosening the
generator mounting clamp screws and moving the generator toward
or away from the engine block. The fan belt should be checked
every few thousand miles to make sure that it is still in good condition. A b'elt that has become worn or frayed or that has separated
[3801
\
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Cooling-system Service
§249
plies should be discarded and a new belt installed. A defective or
loose belt will not only cause overheating of the engine, but may
also result in a nm-down battery, since it cannot drive the generator
fast enough to keep the battery charged.
-I
I
'"
".
\_--",,;-
LOOSEN LOWER "No UPPER
GENERATOR CLAM~
BOLTS
SHOWN AT "A" "a" AND " C"
A SLIGHT AMOUNT
2ND ADJUST FAN BELT tENSION
TO X INCH AS SHOWN
TIGHTEN LOWER CLAMP BOLT
"S" AND RECHECK TENSION
TIGHTEN ClAMP SOLTS "A"
FRONT AND REAR AND "C"
I ST
FIG . 14-6. Method of checking and adjusting fan belt on one
car. The dimension X varies with different models.
FIG. 14-7. Hydrometer to test
antifreeze-s 0 1ution strength.
(E. Edelmann
and Company)
9. Testing antifreeze-solution strength. The strength of the antifreeze solution must not be below that required to furnish adequate
protection in the lowest temperatures expected. The strength of the
solution is tested by use of a special antifreeze-solution hydrometer
(Fig. 14-7), which measures its specific graVity, or heaviness. The
so-called "permanent" antifreeze compounds (ethylene glycol) are
heavier than water, while alcohol-base antifreeze compounds are
lighter than water. The specific-gravity reading will determine
what percentage of the solution is water and what percentage is
antifreeze compound. Then, by reference to a chart, the lowest
[381]
§250
Automotive Fuel, Lubricating, and Cooling Systerns
temperature at which the solution will remain a liquid can be
determined. Additional antifreeze compound can be added if
required.
§250. Care of cooling system Care of the cooling system includes
not only normal maintenance operations such as filling the radiator,
keeping the fan belt tight, and lubricating the water pump when
required, but also diagnosis of trouble in the cooling system and the
necessary corrective measures.
§251. Trouble diagnosis Complaints that may lead the mechanic
to check the cooling system include slow warm-up and overheating.
Slow warm-up could be caused by a thermostat that fails and remains open. This causes the water to circulate between the radiator
and the engine block, even when the engine is cold, and makes it
necessary for the engine to run for a longer period of time before
reaching operating temperature. Overheating, when due to trouble
in the cooling system, is most often caused by accumulations of rust
and scale, defective hose or connections, malfunctioning of the
water pump or thermostat, or a loose or defective fan belt. If the
engine overheats without the radiator's becoming normally warm,
and if the fan belt is tight and in good condition, the thermostat is
probably not opening and will, therefore, require replacement. If
the radiator is hot, test the water pump by pinching closed the
upper hose by hand as described in §249. If the thermostat and
water pump seem to be operating normally and the hose appears to
be in good condition, the overheating, if actually caused by troubles
in the cooling system, is probably due to accumulations of rust or
scale in the cooling system. Such rust or scale should be cleaned and
flushed out (§252). The water may boil after the engine has been
turned off; this is called after boil. This could happen, for example,
after a long, hard drive. The engine has so much heat in it (though
it has not actually overheated) that after the engine is turned off,
the water in the cooling system boils (Fig. 14-8), due to the fact
that it is still absorbing heat from the engine, which it cannot get
rid of because the cooling system is no longer working.
Boiling can also occur if the radiator has frozen up. This hinders
or stops the circulation of the cooling water. Consequently, the
water in the water jackets becomes so hot that it boils.
It must be remembered that there are other causes of engine
[382]
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Cooling-system Service
§252
overheating, which have nothing to do with conditions in the cooling system. High-altitude operation, insufficient oil, overloading of
the engine, hot-climate operation, improperly timed ignition, long
periods of low-speed or idling operation-any of these may cause
overheating of the engine. See Automotive Engines (another book
in the McGraw-Hill Automotive Mechanics Series) for more information on overheating of engines.
STEAM
-~
---------
FIG. 14-8. After-boil of water after engine is stopped.
The cooling system should be
cleaned at periodic intervals to prevent the accumulation of excessive rust and scale. Accumulated rust and scale can be loosened
by a good cleaning compound. There are various types of cleaning
compounds; all must be used carefully in accordance with the
manufacturer's instructions. A general cleaning procedure is outlined below. If considerable scale and rust have accumulated, it
may be that cleaning alone will not remove it all. In this case, the
radiator and engine water jackets must be flushed out with special
heater can be flushed out at the same time (Fig. 14-11). Some car
air-pressure guns as shown in Figs. 14-9 and 14-10. The hot-water
manufacturers recommend reverse flushing; that is, the water is
forced through the radiator and water jackets in the opposite
[383]
§252. Cleaning the cooling system
Automotive Fuel, Lubricating, and Cooling Systems
§252
14-9. Reverse Hushing of radiator.
(Kent-Moore Organization, Inc.)
FIG.
FIG . 14-10. Reverse flushing of engine
water jackets. (Kent-Moore Organization, Inc.)
direction to that in which the water normally circulates. This gets
behind the scale and loosens it so that it will be flushed out.
1. Cooling-system cleaning procedure. Completely drain the
system by b,pening drain cocks (Fig. 14-12). Add cleaning compound and fill system with water. Run engine on fast idle for
[384]
I
\
.
Cooling-system Service
§252
at least 30 minutes after engine reaches operating temperature.
Completely drain system again, add neutralizer (if cleaner requires its use), fill with water, and run engine at fast idle for at
least 5 minutes. Drain system, refill with water, and run for at least
5 minutes after water has reached operating tempel·ature. Then
FIG. 14-11. Reverse flushing of hot-water heater. (Kent-Moore Organization,
Inc.)
14-12. Locations of drain cocks in radiator and engine block on one car.
(Plymouth Division of Chrysler Corporation)
FIG .
drain and refill once again, this time with antifreeze (if it is to be
used).
NOTE: During the procedure, keep the radiator covered so engine develops as much heat as possible. Otherwise, the engine might
not get hot enough to make the thermostat open wide. This would
slow water circulation and reduce the cleaning effect.
[385]
Automotive Fuel, Lubricating, and Cooling Systems
§252
2. Cleaning radiator air passages. At the same time that the
cooling system is cleaned, the radiator air passages should be
cleaned out. This can be done by blowing them out, from back to
front, with compressed air. This removes bugs, leaves, and dirt that
could clog the air passages and reduce the cooling efficiency of
the radiator.
3. Flushing radiator. If cleaning alone does not remove all the
accumulated rust and scale, the radiator and water jackets should
be flushed. This job is done with a flushing gun that uses air pres-
sure to force the water through. The radiator can be straight-flushed
or reverse-flushed. For reverse flushing, a new hose is attached
to the lower tank of the radiator, and a leadaway hose is attached to the upper tank (Fig. 14-13). The water will, of course,
drain out as this is done. Clamp flushing gun in hose to lower tank,
as shown, and turn on water to fill radiator. When water runs out the
leadaway hose, apply air pressure to force water out. Apply the pressure gradually, to avoid damaging the radiator. Sudden full-pressure
application might rupture the radiator core. Refill radiator and
again apply air pressure. Repeat until water running from leadaway
hose is clean.
To straight-flush the radiator, follow the above procedure but
attach leadaway hose to the lower tank of the radiator and the flush[386]
\
\
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Cooling-system Service
§252
ing-gun hose to the upper tank. This will circulate the water
through the radiator in the normal direction.
4. Flushing engine water iackets. Engine water jackets also may
be straight-flushed or reverse-flushed. Some engine manufacturers
warn that seals and other engine parts may be damaged if their
engines are reverse-flushed. Make sure the specifications permit
reverse flushing before doing the job. To reverse-flush, remove the
thermostat and attach the flushing gun to the thermostat housing
with a short length of hose (Fig. 14-14). The illustration does not
show a leadaway hose from the water-pump inlet, but to avoid getting water all over the engine, it is best to use a leadaway hose.
FIG.
14-14. Reverse-flushing engine water jackets.
Fill the water jackets with water, and then apply air. Repeat as for
the radiator until the water runs clear from the leadaway hose.
To straight-flush the water jackets, follow the above procedure,
but attach the leadaway hose to the thermostat housing and the
flushing-gun hose to the pump-inlet connection.
Caution: Do not apply too much air pressure or sudden bursts of
pressure. This might damage engine seals, gaskets, or other parts.
5. Refilling system. When the cooling system has been cleaned,
the thermostat replaced, and all hoses and clamps reconnected,
the system should be refilled. Since the water that is put in will
probably be cold, the thermostat may close and prevent quick filling. With the thermostat closed, air is trapped below the thermostat
in the engine water jackets (Fig. 14-15). The thermostat usually has
[387]
Automotive Fuel, Lubricating, and Cooling Systems
§253
a small hole or two that permits this air to leak out. But it takes a
little time for the air to escape. This means that you may have to fill
and refill the radiator several times, waiting each time for some of
the trapped air to get out. Then, as a final step, the engine should
FIG. 14-15. Air trapped back of closed thermostat as engine cooling system is
filled.
be started and run long enough for the thermostat to heat up and
open. After this happens, more water can be added to make sure
the system is filled.
§253. Locating and repairing radiator leaks Leaks in the radiator
core are usually obvious, since telltale scale marks or watermarks
will form on the outside of the core below the leaks. An accurate
way to locate radiator leaks is to remove the core from the car, drain
out all the water, close the openings at top and bottom, and immerse
the core in water. Air bubbles will escape from the core through
any leaks. Small leaks may sometimes be repaired without removing
the radiator from the car, by use of certain liquid compounds
poured into the radiator. These compounds, seeping through the
. leaks, har~en
upon coming in contact with the air, sealing off the
openings. A more effective way of repairing leaks is to solder them.
If there '~re
several leaks at various places in the core, it may not
[388]
,
\
\
\
Cooling-system Service
§254
be worthwhile to attempt repair, since the core is probably corroded
to a point where other leaks would soon develop.
Removing a radiator core is a relatively simple job although there
is a considerable amount of work involved. The procedure varies
somewhat from car to car but, in general, is as follows. First, drain
the engine and radiator by opening the drain cocks in the radiator
and engine block. Figure 14-12 shows the locations of these two
cocks on one car. Locations vary somewhat from one make to
another. With the cooling system drained, detach the upper and
lower radiator hoses. Remove any support bolts, horns, wiring
harness, and so forth, that might interfere with core removal. With
these parts out of the way and the core loose, lift it straight up and
off the car.
§254. Water-pump service The water pump is a relatively simple
mechanism which requires little service in normal operation. Some
pumps require periodic lubrication; others, with sealed ball bearings, require no lubrication. If the pump develops noise or leaks or
becomes otherwise defective, it must be removed for repair. The
procedures of removal, repair, and replacement vary for different
cars. Typical procedures follow.
1. Chevrolet. To remove water pump, drain cooling system by
opening drain cocks, disconnect hose from pump, remove fan belt,
take out pump attaching screws, and lift off pump.
a. To disassemble pump, take off fan, pump-plate attaching
screws, and pump plate.
h. Then use special puller to pull fan pulley from pump shaft
(Fig. 14-16). It is very important to use this tool correctly in
order not to damage the pulley, shaft, or bearing. Note particularly that the puller plate should be square with the pulley
face.
c. With the pulley off, put the pump in a vise, and use a long
drift punch to remove bearing retainer from pump body.
d. Then, with large end of pump up, put pump on arbor press
with pump supported on the milled shoulder of the pump
body. Use arbor slightly smaller than diameter of pump shaft,
and press shaft and bearing assembly out of the pump body
and rotor. Lift rotor from pump body, and discard the old
seal assembly.
[389]
Automotive Fuel, Lubricating and Cooling Systems
§254
e. Before irupecting the pump parts, wash all parts except the
pump-shaft bearing in cleaning solvent. Do not wash the bearing in solvent since this would remove the sealed-in lubricant
and ruin the bearing. If the shaft seems loose in the bearing
assembly, the assembly should be replaced. The thrust-washer
J-1226
PULLER
FIG. 14-16. Using puller to pull fan pulley from pump shaft. (Chevrolet Motor
Division of General Motors Corporation)
seat in the pump body should be smooth and even. If pitted
or scored, the pump should be replaced.
f. To reassemble the pump, first install the pump shaft and bearing assembly in the pump body, applying pressure to the outer
race of the bearing. Press in until the outer race bottoms. Do
not press on the shaft since this might damage the bearing.
g. Then use a short piece of lY2-inch (inside diameter) pipe to
press (in arbor press) the bearing retainer into position on
the pump body and bearing.
h. Examine rubber seal to find the side without the three projections. Cover this side with sealer, and place seal in rotor
bore with the sealer-coated side down. Coat both sides of
thrust washer with a small amount of water-pump grease, and
put wash~r
on top of seal assembly so that the two lugs index
with ,slots in rotor. Lay rotor and seal assembly on bed of arbor
pres
~ and press shaft and housing assembly down over rotor.
Pre on shaft.
[390]
j\
\
I
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Cooling-system Service
§254
i. Check clearance between face of rotor and pump body (Fig.
14-17). It should be 0.010 to 0.035 inch.
j. Then press pulley onto shaft in arbor press until pulley is flush
with end of shaft.
k. Install pump plate on body with new gasket. Tighten and
stake attaching screws. Install fan.
FIG. 14-17. Measuring clearance between face of rotor and pump body. (Chevrolet Motor Division of General Motors Corporation)
2. Plymouth. To remove the water pump, drain the cooling
system by turning the drain cocks (Fig. 14-12), disconnect hose,
remove fan belt, and take out attaching screws so pump can be
lifted off.
a. For disassembly, refer to Fig. 14-18.
h. Take off fan, and drive out the pin from the fan-pulley hub.
c. Remove the water-pump cover, and pull the impeller and
shaft out.
d. If necessary, remove the bushings by driving the front bushing pin into the shaft hole and then using special tool to force
bushings out (Fig. 14-19).
e. Any parts showing wear should be discarded. Always use a
new seal and retaining washer on reassembly. If the seal seat
in the pump body is scored or rough, it should be refaced
with special tool (Fig. 14-21).
f. To reassemble the pump, first insert a new thmst washer in
the pump body, Hat side faCing the fan-pulley hub.
g. Press new bushin,gs into body (if old were removed) with
[391]
§254
Automotive Fuel, Lubricating, and Cooling Systems
special tool shown in Fig. 14-19. The special tool will assure
installation of the inner bushing to a recessed depth of %4
inch as shown in Fig. 14-20.
h. Drill hole in front bushing as shown in Fig. 14-20 with No. 13
drill, and drive in pin. Be sure all burrs are removed from
inside of bushing.
FIG. 14-18. Water pump in disassembled view. (Plymouth Division of Chrysler
Corporation)
1. Body-caver-plate
screw
2. Body-cover plate
3. Impeller
4. Seal-thrust spring
5. Seal retainer
6. Lubricant nipple
7. Seal-retainer washer
8. Shaft rear bushing
9. Shaft-front-bushing
pin
10. Fan-pulley hub pin
11. Body-caver-plate
screw lock washer
12. Body-caver-plate
gasket
13. Impeller pin
14. Body
15. Seal
16. Seal-retainer-washer
lock ring
17. Shaft thrust washer
18.
19.
20.
21.
Shaft front bushing
Shaft
Fan-pulley hub
Body-caver-plate
screw washer
22. Cover plate to cylinder-block gasket
23. Bypass elbow gasket
i. Use special tool to burnish bearings, and reface the seal seat
in the purrip body (Fig. 14-21).
Then assembie seal parts in the impeller. Place special tool on
shaft so seal
slide on to shaft without being damaged.
r
(392]
\ill
i\ ,
\
Cooling-system Service
§254
k. Install seal retainer washer and grease retainer washer on
shaft, compress the seal assembly as far as possible, and install the lock ring. Insert the complete assembly into the pump
body as far at it will go.
FIG. 14-19. Removing bushings from water pump with special tool. (Plymouth
Division of Chrysler Corporation)
THRUST WASHER
FRONT BUSHING
ASSEMBLE FRONT
BUSHING WITH OIL
GROOVE ON TOP AND
GROOVED END OUT
~2.78-i
2.782
FIG. 14-20. Locations and measurements of bushings in water pump. (Plymouth
Division of Chrysler Corporation)
l. Make sure the flat spots on the shaft interlock with the flats
of the thrust washer. Press the hub onto the shaft, leaVing
0.003-inch (or between 0.0005- and 0.005-inch) clearance
between the front bushing and hub.
[393]
§254
Automotive Fuel, Lubricating, and Cooling Systems
m. Drill a hole through the hub and shaft, and install pin. Peen
over ends of pin so it will hold.
S. Ford. To remove the water pump (Fig. 14-22), drain the
cooling system, disconnect hose, take off fan belt, remove mounting
bolts, and take off pump. In some cases, it may be necessary to
REFACING
SEAT
FIG. 14-21. Burnishing bushings and refacing seal seat with special tool, Hous-
ing has been cut away to show tool. (Plymouth Division of Chrysler Corporation)
loosen the engine mounting bolts and raise the engine so that
mounting bolts clear pump attaching bolts.
a. To disassemble the pump, remove the pulley and bearing lock
ring located at the pulley end of the hOUSing, and press the
impeller off the shaft by pressing the shaft and bearing assembly out through the front of the hOUSing. Use arbor
slightly smaller than shaft. Press the seal out of the hOUSing
and, if necessary, remove the snap ring from inside the
hOUSing.
b. To assemble the pump, replace the snap ring inside the housing, and press a new seal into the housing with the carbon
washer of the seal facing the impeller. Use special seal replacer
tool, an,p. make sure it contacts only the outer metal part of
the seal. Otherwise the carbon sealing washer may be dam[394J
\.
Cooling-system Service
§254
aged. Position the slinger on the shaft with the flanged end
toward the bearing, and insert the shaft and bearing assembly
into the housing at the front end. Press the shaft and bearing
assembly into the housing, using special hollow tool to exert
pressure on the outer bearing race only. Do not press on the
shaft; this will damage the bearing. Install the bearing lock
ring in the groove in the housing. Press pulley onto the shaft,
Sfinqer
SOfl~"'\_ bevnnq~ ~
b '
'~
•
e
Seq!
Impeller
FIG. 14-22. Disassembled view of water pump. (Ford Motor Company)
and press impeller on shaft to proper position. Clearance between the impeller blades and housing should be between
0.031 and 0.040 inch.
CHAPTER CHECKUP
NOTE: Since the following is a chapter review test, you should review
the chapter before taking the test.
Here is your checkup on the final chapter of the Automotive Fuel,
Lubricating, and Cooling Systems book. You have made wonderful progress in your studies of this book and must feel proud at having "stuck to
it" until you finished it. The information you have learned from the book
gives you the basic background you need to become a specialist in the
engine systems discussed, or to become a good, all-around automotive
mechanic. Take the checkup that follows to make sure you have the essential facts in the chapter well in mind. Write down your answers in
your notebook.
[395]
Automotive Fuel, Lubricating, and Cooling Systems
Picking Out the Right Answer
Several answers are given for each question or statement below. Read
each statement carefully; then decide which of the several answers that
follow is the correct one. Write down the completed statement or answered question in your notebook.
1. Accumulation of rust and scale in the engine-cooling system will
cause
slow warm-up
reduced heating capacity
overheating
2. If the thermostat is stuck closed, the engine will
warm up
slowly
overheat
fail to start
3. If the thermostat is stuck open, the engine will
warm up slowly
overheat
fail to start
4. The strength of the antifreeze solution in the cooling system is
hydrometer
bachecked by a special
micrometer
rometer
thermometer
5. Exhaust-gas leakage into the cooling system is most likely to be due
to a defective
cylinder-head gasket
manifold gasket
water pump
6. Air will be drawn into the cooling system if there are leaks at any
point behveen the
water pump and ;ackets
radiator and
thermostat and radiator
water pump
7. When the water boils after the engine has been turned off after a
hard run, the condition is known as
overheating
hard
running
clogged radiator
after-bailing
8. When reverse-Hushing the radiator, the Hushing gun is connected to
the
upper tank
pump inlet
lower tank
9. When reverse-Hushing the engine water jackets, the Hushing gun is
connected to the
upper tank
lower tank
thermopump inlet
stat housing
10. When refilling the system with cold water causes the engine to be
cooled, air may be trapped
below the thermostat
above
the thermostat
in the radiator
Correcting the Lists
In each of the lists below, you will find one item that does not belong.
Write down each list in your notebook, but do not write down the item
that does not belong.
l. Engine overheating can be caused by: accumulations of rust and
scale, thermostat stuck closed, thermostat stuck open, loose fan belt,
defective hrse, defective water pump
[396)
\
\ '.
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\
Cooling-system Service
2. Slow engine warm-up can be caused by: thermostat stuck open,
manifold heat-control valve stuck, thermostat stuck closed
3. Tests of the cooling system include testing the: thermostat, radiator
(for restrictions), hose and hose connections, water pump, fuel pump,
fan belt, antifreeze strength
4. Items in the cooling system that can be flushed with the flushing gun
include the: radiator, engine water jackets, filter, car heater
5. Bailing of the water can occur due to: radiator freezing, after-boil,
thermostat stuck closed, high-altitude operation, broken fan belt,
thermostat stuck open
Procedures
In the following, you are asked to write down certain servlcmg procedures or to list various troubles and explain them. Write these down
in your notebook. The act of writing them down not only helps you
remember the important points, but also makes your notebook a very
valuable reference, in which you can look up things that might have
escaped your memory for the moment.
1.
2.
3.
4.
5.
6.
7.
8.
9.
How is the thermostat tested?
How can the cooling system be tested for rust and scale?
How can you check the radiator for restrictions?
How can the water pump be checked on the car?
How can the system be tested for exhaust-gas leakage?
How is the fan belt adjusted?
How is the strength of the antifreeze solution tested?
What conditions in the cooling system will cause engine overheating?
What condition in the cooling system would cause slow engine
warm-up?
10. Describe how a cooling system is flushed out.
11. Describe how to remove a radiator core, locate a leak, and repair
the leak.
12. Describe step by step, how to remove a water pump from a car,
disassemble, inspect, and reassemble it.
SUGGESTIONS FOR FURTHER STUDY
Watch how the mechanics at the automotive service shop clean out
cooling systems and take off radiators and water pumps. Notice how
they tear down and repair water f'umps and what special equipment
they need for this job. Study car shop manuals of the various makes of
cars, and notice the different methods of repair these manuals recommend. Write down in your notebook any important facts you run across
in the manuals or in the shop.
[397]
Appendix A: Exhaust-gas
Analyzers
EXHAUST-GAS ANALYZERS are devices that are used to determine
the proportions of the fuel and air entering the combustion chamber by
analyzing the exhaust gas produced by combustion of the fuel and air.
The gases found in the exhaust from the combustion chamber vary according to the proportions of gasoline and air that entered into the combustion. Three types of exhaust-gas analyzer are in use: the thermalconductivity, hot-wire-catalysis, and relative-density.
1. Thermal conductivity "Thermal conductivity" is a term that expresses the ease with which heat is conducted through a substance.
Some substances allow heat to pass through readily; others, such as
asbestos, resist its passage. The various gases found in exhaust gas have
BATTERY
Schematic wmng diagram
of a thermal-conductivity tester for
testing exhaust gas.
FIG. A-I.
STANDARD
OELL
varying degrees of thermal conductivity and pass heat with varying
degrees of ease. Thus measurement of the thermal conductivity of the
exhaust gas will accurately determine the proportions of carbon dioxide,
carbon monoxide, hydrogen, and oxygen in the exhaust gas. These proportions depend on the air-fuel ratio that is delivered to the engine.
The thermal-conductivity tester (Fig. A-I) consists of a battery, two
resistances, a sensitive ammeter (or galvanometer), and two cells in
which are suspended platinum-wire spirals. The flow of current through
the two spirals heats them, and they increase in temperature until they
[399]
Automotive Fuel, Lubricating and Cooling Systems
stabilize; that is, until the heat they give off balances the heat created in
them by the current flow. The heat they give off travels through the intervening air to the walls of the cells. When the air surrounding the two
spirals is identical, the two spirals will stabilize at the same temperature
and will thus be drawing the same amount of current. If air of a different
thermal conductivity is introduced into one cell, the spiral in that cell
will stabilize at a different temperature. Since the resistance of platinum
wire varies with temperature, that spiral will now pass a different
amount of current. This means that the ammeter, which reads zero
when both circuits pass the same amount of current, now begins to
register the difference in current flow in the two circuits. This is because part of the current now passes through the ammeter in order to
flow through the platinum wire having the lower resistance. The application of this principle to exhaust-gas analysis is obvious. Air is introduced
into the standard cell, while exhaust gas passes through the exhaust-gas
cell. The difference in thermal conductivity between the two is indicated
by the ammeter reading. The ammeter dial is usually marked off to read
air-fuel ratio directly, so that no calculations are necessary.
2. Hot-wire catalysis In some respects, the hot-wire-catalysis exhaustgas analyzer (Fig. A-2) is similar to the thermal-conductivity analyzer.
BATTER'(
FIG. A-2. Schematic wmng diagram
of a hot-wire-catalysis exhaust-gas
analyzer.
EXHAUST-
GAS CELL
Both make use of a platinum wire heated by electric current and a
sensitive ammeter that records difference in resistance in two parallel
circuits. The hot-wire catalysis, however, uses a single straight platinum
wire enclosed in a cell. The resistances are so balanced that the same
amount of ?urrent is passing through each side of the two parallel
circuits. The\current passing through the straight platinum wire in the
exhaust-gas\ cell heats the wire to a red heat. Under this condition, and
before the ~st
begins, the ammeter registers zero. Exhaust gas, mixed
with a definite ratio of air, is then passed through the exhaust-gas cell.
[400]
\,
\
Appendix A: Exhaust-gas Analyzer
Any unburned components in the exhaust gas now have another chance
to burn as they pass the red-hot wire. They do burn, and this further
raises the temperature of the wire. The more unburned components in
the exhaust gas, the more combustion, and the higher the temperature
of the wire. This increase of temperature causes an increase in resistance
and a consequent reduction of current flow in the platinum wire. The
ammeter registers this difference of current flow, since it will pass current
seeking to flow through its resistance rather than through the wire. The
ammeter dial is marked off to read air-fuel ratio directly.
3. Relative density The density of the exhaust gas is determined by
the proportions of its various components, each of which has a different
density. Thus, by determining the density of the exhaust gas, the result
can be evaluated in terms of the air-fuel ratio. The type of analyzer
that measures the denSity of the exhaust gas relative to air consists of
two fans rotated in two chambers by a motor. Both rotate at the same
speed; one in air, the other in exhaust gas. The air or gas movement
produced by the fans causes two impulse wheels to move. The two impulse wheels are linked together, and one of them has a pointer registering on a dial. Since the exhaust gas is heavier or denser than air, the
impulse wheel in the exhaust-gas chamber will turn more than will the
impulse wheel in the air chamber. This causes the pointer to move
across the dial and register directly the air-fuel ratio that produced the
exhaust gas.
[401]
Appendix B: Glossary
THIS GLOSSARY of automotive terms used in the book is designed
to provide a ready reference for the student. The definitions may differ
somewhat from those given in a standard dictionary; they are not
intended to be all-inclusive, but have the purpose of serving as reminders
so that the student can quickly refresh his memory on automotive terms
of which he may be unsure. More complete definitions and explanations
of the terms are found in the text.
In automobile service, a substance used for cutting, grinding,
or polishing metal.
Accelerator The foot-operated pedal linked to the carburetor throttle
valve.
Accelerator pump In the carburetor, a pump linked to the accelerator,
which momentarily enriches the mixture when the accelerator pedal
is depressed.
Air bleed An opening into a gasoline passage through which air can
pass (or bleed) into the gasoline as it moves through the passage.
Air cleaner The device mounted on the carburetor, through which air
must pass on its way into the carburetor air horn. It filters out dirt
and dust particles and also silences the intake noise.
Air-cooled engine An engine that is cooled by passage of air around the
cylinders and not by passage of a liquid through water jackets.
Air-fuel mixture Mixture delivered to engine by carburetor.
Air horn In the carburetor, the tubular passage through which the incoming air must pass.
Air line A hose or pipe through which air passes.
Air pressure Atmospheric pressure (14.7 psi at sea level) or pressure
of air produced by pump, by compression in engine cylinder, etc.
Antifriction bearing Type of bearing in which moving parts are in
rolling contact; ball, roller, or tapered roller bearing.
Antiknock In engine fuels, the property that opposes knocking.
Antipercolator The device in the carburetor that opens a vent when the
throttle is closed, to permit release of fuel vapors in the high-speed
circuit so that fuel vapor will not push fuel out of the high-speed
nozzle.
Atmospheric' pressure Pressure of the atmosphere, or air, due to its
weight\pressing downward. Average is 14.7 psi at sea level.
[402]
..
Abrasive
\
\
Appendix B: Glossary
Atomization The spraying of a liquid that makes it a very fine mist.
Automatic choke A choke that positions the choke valve automatically
in accordance with engine temperature.
Pre-explosion of air-fuel mixture so that explosion passes the
still-opened intake valve and flashes back through the intake manifold.
Balanced carburetor Carburetor in which the float bowl is vented into
upper air horn, below air cleaner, to eliminate effects of clogged
cleaner.
Ball check valve A valve consisting of a ball and seat. Fluid can pass
in one direction only; when it attempts to flow the other way, it is
checked by the ball seating on the seat.
Barrel The air horn in the carburetor; used particularly to refer to that
part of the air horn in which the throttle valve is located.
BOC Bottom dead center, which see.
Bearing Generally, the curved surface on a shaft or in a bore, or the
part assembled onto one or into the other to permit relative rotation
with minimum wear and friction.
Bellows A device, usually metal, that can lengthen or shorten much
like an accordian. The thermostat in the cooling system is usually
a bellows.
Bimetal Referring to the thermostatic bimetal element made up of two
different metals with different heat-expansion rates; temperature
change produces a bending or distorting movement.
Blow-by Leakage of compressed air-fuel mixture or burned gases from
the combustion chamber, past the piston rings, and into the
crankcase.
Body The assembly of sheet-metal sections, together with windows,
doors, seats, and other parts, that provides an enclosure for the
passengers, engine, etc.
Borderline knock test A test used to establish octane rating, or knock
resistance, of different fuels.
Borderline lubrication Type of lubrication resulting when greasy friction
exists. Moving parts are coated with a very thin film of lubricant.
Bore Diameter of engine cylinder hole; also may be diameter of any
hole, as, for instance, the hole in which a bushing fits.
Bottom dead center The piston position at which the piston has moved
to the bottom of the cylinder and the center line of the connecting
rod is parallel to the cylinder walls.
Brake horsepower The power delivered by the engine which is available for driving the vehicle.
[403]
Backfiring
Automotive Fuel, Lubricating, and Cooling Systems
The opening that allows air to circulate in the crankcase and
that is part of the crankcase ventilator, which see.
Burnisher A cylindrical tool with integral collars that increase in diameter from one end of the tool to the other.
Burr A featheredge of metal left on a part being cut with a file or other
cutting tool.
Bushing A sleeve placed in a bore to serve as a bearing surface.
Butane One form of liquefied petroleum gas, which see.
Butterfly The choke or throttle valve.
Bypass filter Type of oil filter in which only some of the oil from the oil
pump flows through the RIter. The remainder of the oil bypasses the
filter on its way to engine parts.
Caliper A measuring tool that can be set to measure the thickness of
a block, diameter of a shaft, or bore of a hole (inside caliper).
Cam An irregularly shaped moving part designed to move or alter the
motion of another part.
Cam ground Refers to oval-shaped piston, so ground as to permit piston
to expand and assume a round shape when hot.
Camshaft The shaft in the engine which has a series of cams for operating the valve mechanisms. It is driven by gears or sprockets and
chain from the crankshaft.
Carbon A substance deposited on engine parts by the combustion of
the fuel. Carbon forms on pistons, rings, valves, etc., inhibiting their
action.
Carbon dioxide A gas resulting from burning of fuel.
Carbon monoxide A poisonous gas produced by a running gasoline
engine.
Carburetion The actions that take place in the carburetor: converting
liquid fuel to vapor and mixing it with air to form a combustible
mixture.
Carburetor The device in the fuel system which mixes air and gasoline
(vaporizing the gasoline as it does so) in varying proportions to
suit engine operating conditions.
Cetane Ignition quality of diesel fuel. A high-cetane fuel ignites more
easily (at lower temperature) than a low-cetane fuel.
CFR Uniontown road test A road test used to establish octane rating of
different fuels.
Change of state Changing of a substance from solid to liquid, or from
liquid to vapor, or vice versa.
Chassis The assembly of mechanisms that make up the major operating
part of\ the vehicle. It is usually assumed to include everything
except the car body.
Breather
\
\
l-i \
\
\
Appendix B: Glossary
In the carburetor, a device that chokes off the air flow through
the air horn, producing a partial vacuum in the air horn for greater
fuel delivery and a richer mixture.
Clearance The space between two moving parts or between a moving
and a stationary part, such as a journal and a bearing. Clearance
is considered to be filled with lubricating oil when engine is running.
Coil spring A spring made up of an elastic metal, such as steel, formed
into a wire or bar and wound into a coil.
Combination fuel pump A fuel pump with which a vacuum pump for
operating the windshield wipers has been combined.
Combustion In the engine, the rapid burning of air-fuel mixture in
cylinder.
Combustion chamber The space at the top of the cylinder and in the
head in which combustion of the air-fuel mixture takes place.
Compensating circuit A special circuit in some carburetors to compensate for variations in fuel discharge from main nozzle. Compensating-circuit fuel nozzle discharges more fuel when nozzle discharges
less, and vice versa, so that a balanced air-fuel mixture is delivered
at all times.
Compression gauge A device for testing the amount of pressure developed in the engine cylinder during cranking.
Compression ratio The ratio between the volume in the cylinder with
the piston at BDC and the volume with the piston at TDC.
Compression rings The upper ring or rings on a piston, designed to hold
the compression in the cylinder and prevent blow-by.
Compression stroke The piston stroke from BDC to TDC during which
both valves are closed and the air-fuel mixture is compressed.
Condensation The changing of a vapor to a liquid due to temperature,
pressure, or other changes.
Connecting rods In the engine, linkages between the cranks on the
crankshaft and the pistons.
Cooling system In the engine, the system that removes heat from the
engine and thereby prevents overheating. It includes water jackets,
water pump, radiator, and thermostat.
Crank A device for converting reciprocating motion into rotary motion,
or vice versa.
Crankcase The lower part of the engine, in which the crankcase rotates. The upper part of the crankcase is lower section of the cylinder block, while the lower part is made up of the oil pan.
Crankcase dilution Dilution of the lubricating oil in the oil pan by the
seepage of liquid gasoline down the cylinder walls.
Choke
[405]
Automotive Fuel, Lubricating, and Cooling Systems
The device that permits air to flow through engine crankcase when engine is running.
Crankpin The bearing surface on a crank of the crankshaft, to which
the connecting rod is attached.
Crankshaft The main rotating member, or shaft, of the engine, with
cranks to which the connecting rods are attached.
Cycle In the engine, the four piston strokes (or two piston strokes)
that complete the working process and produce power.
Cylinder In the engine, the tubular opening in which the piston moves
up and down.
Cylinder block The basic framework of the engine in and on which
the other engine parts are attached. It includes the engine cylinders and the upper part of the crankcase.
Cylinder head The part of the engine that encloses the cylinder bores.
Contains water jackets and, on I-head engine, the valves.
Degree 1/360 part of a circle.
Detergent A chemical sometimes added to the engine oil, designed to
help keep the internal parts of the engine clean by preventing the
accumulation of deposits.
Detonation In the engine, excessively rapid burning of the compressed
charge which results in knock, which see.
DG oil Lubricating oil for average, or normal, diesel-engine service.
Dial indicator A gauge that has a dial face and needle to register movement. Used to measure variations in size, movements too small to be
measured conveniently by other means, etc.
Diaphragm A flexible membrane, in automotive components usually
made of fabric and rubber, clamped at the edges, and usually
spring-loaded; used in fuel pump, vacuum pump, distributor, etc.
Diesel cycle An engine cycle of events in which air alone is compressed
and fuel oil injected at the end of the compression stroke. The heat
produced by compressing the air ignites the fuel oil.
Dip stick The oil-level indicator stick.
Downdraft carburetor A carburetor in which the air horn is so arranged
that the air passes down through it on its way to the intake manifold.
Drill Also called twist drill. A cylindrical bar with helical grooves and
a point, for cutting holes in material. Also refers to the device that
rotates the drill.
Dry friction The friction between two dry solids.
DS oil Lubricating oil for severe, or heavy-duty, diesel-engine service.
Dual carburetors Carburetors with two air horns, fuel nozzles, throttle
vales~
idle circuits, etc.
Crankcase ventilator
[406]
't\
, \
\,
Appendix B: Glossary
Dynamometer A device for measuring power output of an engine.
Eccentric Off center.
Economizer valve The mechanism in the carburetor that permits a rich
mixture for full-load engine operation but leans the mixture for
more economical operation on part throttle.
Efficiency Ratio between the effect produced and the energy expended.
Electric system In the automobile, the system that electrically cranks
the engine for starting, furnishes high-voltage sparks to the engine
cylinders to fire the compressed air-fuel charges, lights the lights,
operates the heater motor, radio, etc. Consists, in part, of starting
motor, wiring, battery, generator, regulator, ignition distributor,
ignition coil.
Energy Energy is the capacity or ability to do work.
Engine The assembly that bums fuel to produce power, sometimes
referred to as the power plant.
Engine tune-up The procedure of checking and adjusting various engine components so that engine is restored to top operating
condition.
Ethyl Tetraethyllead, which see.
Evaporation The change of a liquid to a vapor, or gas.
Exhaust-gas analyzer A device for analyzing exhaust gases to determine
carburetor action.
Exhaust manifold The part of the engine that provides a series of
passages through which burned gases from the engine cylinders
can How.
Exhaust muffler The device in the exhaust line that muffles the sound
of exhaust.
Exhaust stroke The piston stroke from BDC to TDC during which the
exhaust valve is open so that the burned gases are forced from the
cylinder.
Exhaust valve The valve that opens to allow the burned gases to exhaust from the engine cylinder during the exhaust stroke.
Expansion plug A plug that is slightly dished out. When driven into
place, it is Hattened and expanded to fit tightly.
Extreme-pressure lubricant A special lubricant for use in hypoid-gear
differentials.
Fan The device on the front of the engine that rotates to draw a
blast of cooling air through the radiator.
Fast idle The mechanism on the carburetor that holds the throttle
valve slightly open when the engine is cold so that the engine will
idle at a higher rpm when cold.
[407]
Automotive Fuel, Lubricating, and Cooling Systems
Strips of metal of accurately known thickness, used to
measure clearances.
File A cutting tool with a large number of cutting edges arranged along
a surface.
Filter That part in the lubricating or fuel system through which fuel,
air, or oil must pass so that dust or dirt is removed.
Firing order The order in which the engine cylinders fire, or deliver,
their power strokes.
Float bowl In the carburetor, the reservoir from which gasoline feeds
into the passing air.
Float circuit The circuit in the carburetor that controls entry of fuel
and fuel level in the float bowl.
Float level The float position at which the needle valve closes the fuel
inlet to the carburetor to prevent further delivery of fuel.
Flywheel The rotating metal wheel, attached to the crankshaft, that
helps even out the power surges from the power strokes and also
serves as part of the clutch and engine-cranking system.
Four-barrel carburetor A carburetor with four air horns. In effect, two
two-barrel, or dual, carburetors in a single assembly. Used on
several V-8 engines.
Four cycle Short for four-stroke cycle, which see.
Four-stroke cycle The four operations of intake, compression, power,
and exhaust, or four piston strokes, that make up the complete
cycle of events in the four-stroke-cycle engine.
Friction The resistance to motion between two bodies in contact with
each other.
Friction bearing Type of bearing in which moving parts are in sliding
contact; sleeve, guide, or thrust bearing.
Fuel gauge The gauge that indicates to the driver the height of the
fuel level in the fuel tank.
Fuel injector A device in a diesel-engine fuel system for injecting fuel
oil into the cylinder.
Fuel jet
See iet.
Fuel line The pipe or tube through which fuel travels from the tank
to the fuel pump and from the pump to the carburetor.
Fuel nozzle The tube in the carburetor through which gasoline feeds
from the float bowl to the passing air.
Fuel system In the automobile, the system that delivers to the engine
cylinders the combustible mixture of vaporized fuel and air. It
consists \)f fuel tank, lines, gauge, carburetor, manifold.
Fuel tank rhe metal tank that serves as a storage place for gasoline.
\
[408]
:\
Feeler stock
Appendix B: Glossary
Type of oil filter in which all the oil from the oil pump
flows through the filter.
Full throttle Wide-open throttle position with accelerator pressed all
the way down to floor board.
Gasket A flat strip, of cork or other material, placed between two
surfaces to provide a tight seal between them.
Gasket cement An adhesive material used to apply gaskets.
Gasoline A hydrocarbon suitable as an engine fuel, obtained from
petroleum.
Gear lubricant A type of grease or oil designed especially to lubricate
gears.
Gear-type pump A pump using a pair of matching gears that rotate;
meshing of the gears forces oil (or other liquid) from between the
teeth through the pump outlet.
Generator The part of the electric system that converts mechanical
energy into electric energy for lighting lights, charging the battery,
operating the ignition system, etc.
Goggles SpeCial glasses worn over the eyes to protect them from
flying chips, dirt, or dust.
Governor A device, often installed under the carburetor, that prevents
engine speed from exceeding a preset maximum.
Gravity The attractive force between objects that tends to bring them
together. A stone dropped from the hand falls to the earth because
of gravity.
Grease Lubricating oil to which thickening agents have been added.
Greasy friction The friction between two solids coated with a thin
film of oil.
Grinding wheel An abrasive wheel used for grinding metal objects
held against it.
Heat-control valve In the engine, a thermostatically operated valve
in the exhaust manifold for varying heat to intake manifold with
engine temperature.
Heat of compression Increase of temperature brought about by compression.
Heptane A reference fuel that knocks very easily, used in various
proportions with iso-octane for comparative test of knock characteristics of fuels.
High compression A term used to refer to the increased compressions
of modern automotive engines.
High-speed circuit The circuit in the carburetor that supplies fuel to
the air passing through the air horn during medium- and highspeed, part- to full-throttle operation.
[409]
Full-flow filter
Automotive Fuel, Lubricating, and Cooling Systems
A term referring to the octane rating of a fuel. A
high-test fuel has a high octane rating.
Hone An abrasive stone that is rotated in a bore or bushing to remove
material.
Horsepower A horsepower is a measure of a definite quantity of power;
33,000 ft-lb of work per minute.
Hydrocarbon A compound made of the elements hydrogen and carbon;
gasoline is a hydrocarbon.
Hydrometer A device to determine the specific gravity (roughly the
heaviness) of a liquid. This determination indicates the freezing
point of the coolant in the cooling system, for example.
Idle circuit In the carburetor, the passage through which fuel is fed
when the engine is idling.
Idle mixture The air-fuel mixture supplied to the engine during idle.
Idle-mixture adjustment screw The adjustment screw that can be turned
in or out to lean or enrich the idle mixture.
Idle port The opening into the air horn through which the idle circuit
in the carburetor discharges.
Idling speed The speed at which the engine runs without load when
the accelerator pedal is released.
Ignition coil That part of the ignition system which acts as a transformer to step up the battery voltage to many thousands of volts;
the high-voltage surge then produces a spark at the spark-plug gap.
Ignition distributor That part of the ignition system which closes and
opens the circuit to the ignition coil with correct timing and distributes to the proper spark plugs the resulting high-voltage surges
from the ignition coil.
Ignition system In the automobile, the system that furnishes highvoltage sparks to the engine cylinders to fire the compressed air-fuel
charges. Consists of battery, ignition coil, ignition distributor, ignition
switch, wiring, spark plugs.
Indicated horsepower A measurement of engine power based on power
actually developed in the engine cylinders.
Inertia Property of objects that causes them to resist any change in
speed or direction of travel.
Intake manifold The part of the engine that provides a series of
passages from the carburetor to the engine cylinders through which
air-fuel mixture can flow.
Intake stroke The piston stroke from TDC to BDC during which the
intak~
v\alve is open and the cylinder receives a charge of air-fuel
mixtuiie ..
High-test gasoline
[410]
),
.,
\
\
\
Appendix B: Glossary
The valve that opens to permit air-fuel mixture to enter
the cylinder on the intake stroke.
Iso-octane A reference fuel that shows great resistance to knocking,
used in various proportions with heptane for comparative test of
knock characteristics of various fuels.
Jackets The water jackets that surround the cylinders, through which
the cooling water passes.
Jet A fuel nozzle or calibrated fuel passage in the carburetor.
Knock In the engine, a rapping or hammering noise resulting from exceSSively rapid burning of the compressed charge.
Liquefied petroleum gas A hydrocarbon suitable as an engine fuel obtained from petroleum and natural gas, a vapor at atmospheric
pressure but liquefied if put under sufficient pressure.
Lock nut A second nut turned down on a holding nut to prevent
loosening.
Low-speed circuit The circuit in the carburetor that supplies fuel to
the air passing through the air horn during low-speed, part-throttle
operation.
LPG Liquefied petroleum gas, which see.
Lubrication system The system in the engine that supplies moving
engine parts with lubricating oil.
Main fuel nozzle The fuel nozzle in the carburetor that supplies fuel
when the throttle is partially to fully open.
Manifold The intake or exhaust manifold, which see.
Manifold vacuum The vacuum in the intake manifold that develops as a
result of the vacuum in the cylinders on their intake strokes.
Mechanical efficiency In an engine, the ratio between brake horsepower
and indicated horsepower.
Mechanical octane Octane needs of an engine, resulting from the
mechanical deSign, or shape and relation of parts.
Mechanism A system of interrelated parts that make up a working
agency.
Metering rod A device in the carburetor that enlarges or decreases the
fuel passage to the fuel nozzle, varying fuel delivery for various
throttle openings.
Micrometer A measuring device that measures accurately such dimensions as shaft or bore diameter or thickness of an object.
Mike A slang term for micrometer, which see.
Missing In the engine, the failure of a cylinder to fire when it should.
ML oil Oil for light automotive service.
MM oil Oil for medium, or average, automotive service.
MS oil Oil for severe automotive service.
[411]
Intake valve
Automotive Fuel, Lubricating, and Cooling Systems
In the exhaust, a device, through which the exhaust gases must
pass, that muffies the sound.
Nozzle Fuel nozzle, or jet, through which fuel passes when it is discharged into the carburetor air horn.
Octane A measure of antiknock value of engine fuel.
Oil cleaner The filtering device through which oil passes, which filters
dirt and dust from the oil.
Oil-control rings The lower ring or rings on a piston designed to
prevent excessive amounts of oil from working up into the combustion chamber.
Oil dilution Dilution of oil in the crankcase, caused by leakage of
liquid gasoline from the combustion chamber past the pistons.
Oil filter That part of the lubricating system that removes dirt and dust
from the oil circulated through it.
Oil-level indicator The indicator, usually a "stick," that can be removed
to detennine the level of oil in the crankcase.
Oil pan The detachable lower part of the engine, usually made of
sheet metal, that encloses the crankcase and acts as an oil reservoir.
Oil-pressure indicator Oil gauge that reports to the driver the oil
pressure in the engine lubricating system.
Oil pump In the lubrication system, the device that delivers oil from
the oil pan to the various moving engine parts.
Oil pumping Passing of oil past the piston rings into the combustion
chamber because of defective rings, piston, worn cylinder walls,
etc.
Oil seal A seal placed around a rotating shaft, etc., to prevent escape
of oil.
Oilstone A block of abrasive material bondcd together, used for removing metal.
Orifice A small opening, or hole, into a cavity.
Otto cycle The four operations of intake, compression, power, and exhaust; so named for the inventor of the four-stroke cycle engine, Dr.
Nikolaus Otto.
Petroleum The crude oil extracted from the ground from which gasoline, lubricating oil, and other products are refined.
Ping A metallic rapping sound from engine cylinder, caused by
detonation.
Piston In the engine, the cylindrical part that moves up and down in
the cylinder.
Piston pin 'Also called wrist pin. The cylindrical, or tubular, metal
object\that attaches the piston to the connecting rod.
Muffler
[412]
Appendix B: Glossary
Th~
bearin~s
or ~mhings.
in the piston and upper
end of the connecting rod, III whIch the pIston pin rides.
Piston rings The rings fitted into grooves in the piston. There are two
types, compression rings (for sealing the compression into the combustion chamber) and oil rings (to scrape excessive oil off the
cylinder walls and thereby prevent it from working up into and
burning in the combustion chamber).
Piston skirt The lower part of the piston.
Piston slap Hollow, muffled, bell-like sound made by excessively loose
piston slapping cylinder wall.
Poppet valve A mushroom-shaped valve, widely used in automotive
engines.
Port In the carburetor, an opening or jet through which fuel is discharged into the air horn.
Power The rate of doing work.
Power jet The fuel nozzle that discharges additional fuel into the
high-speed circuit of the carburetor when the throttle is opened
wide.
Power piston The vacuum-operated piston in carburetors that releases
at wide-open throttle to permit delivery of a richer air-fuel mixture.
Power stroke The piston stroke from TDC to BDC during which the
air-fuel mixture burns and forces the piston down, so that the engine
produces power.
Power train The group of mechanisms that carries the rotary motion
developed in the engine to the car wheels; it includes clutch, transmission, propeller shaft, differential, and axles.
Preignition Ignition of the air-fuel mixture in the engine cylinder (by
any means) before the ignition spark occurs at the spark plug.
Press fit A fit so tight, as a piston pin in a pin bushing, for example,
that the pin has to be pressed into place (usually with an arbor
prcss) .
Pressure cap The type of radiator cap used with pressure cooling
systems; it contains a pressure relief valve and a vacuum valve.
Pressure-feed A type of engine lubricating system that makes use of an
oil pump to force oil through tubes and passages to the various
engine parts requiring lubrication.
Pressure regulator The device in an LPG fuel system that reduces the
pressure on the LPG, permitting the fuel to vaporize in readiness
for mixing with air in the carburetor.
Pressure relief valve A valve in the oil line that opens to relieve excessive pressures that the oil pump might develop.
[413]
Piston-pin bearings
Automotive Fuel, Lubricating, and Cooling Systems
A device for measuring power output of an engine (brake
horsepower) .
Propane One type of LPG, which see.
Psi Pounds per square inch; usually used to indicate pressure of a
liquid or gas.
Puller Generally, a service tool that permits removal of one part from
another without damage. Contains a screw or screws that can be
turned to apply gradual pressure.
Quadrijet carburetor Four-barrel carburetor, which see.
Radiator In the cooling system, the device that removes heat from
water passing through it; it takes hot water from the engine and
returns cooled water to the engine.
Radiator cap The cap placed on the radiator filler tube.
Ribbon-cellular radiator core One type of radiator core consisting of
ribbons of metal soldered together along their edges.
Rocker arm A part in the fuel pump, linked to the diaphragm, that
rocks back and forth as its end rides on a cam on the camshaft.
Rotor pump A type of pump using a pair of rotors, one inside the other,
to produce the oil pressure required to circulate oil to engine parts.
Rpm Revolutions per minute.
Scored Scratched or grooved, as a cylinder wall may be scored by
abrasive particles moved up and down by the piston rings.
Scraper A device used in engine service to scrape carbon, etc., from
engine block, pistons, etc.
Screen A fine-mesh screen in the fuel line that prevents the passage
of dirt or dust into the carburetor.
Shim A strip of copper or similar material used, for example, under a
bearing cap to increase bearing clearance.
Sludge Accumulation in oil pan, containing water, dirt, and oil; sludge
is very viscous and tends to prevent lubrication.
Soldering The uniting of pieces of metal with solder, flux, and heat.
Spark plug The assembly, which includes a pair of electrodes and an
insulator, that has the purpose of prOViding a spark gap in the
engine cylinder.
Splash-feed A type of engine lubricating system that depends on
splashing of the oil for lubrication to moving engine parts.
Spring An elastic device that yields under stress or pressure but returns to its original state or position when the stress or pressure
is remo~d.
Storage bat~'ry
The part of the electric system which acts as a reservoir
for electric energy, storing it in chemical form.
.\
[414]
\
Prony brake
\,
\
\
Appendix B: Glossary
In an engine, the distance that the piston moves from BDC to
TDC.
Stud A headless bolt threaded on both ends.
Tachometer A device for measuring engine speed, or rpm.
Tank unit The unit of the fuel-indicating system that is mounted in the
fuel tank.
Tap A special cutting tool for cutting threads in a hole.
Taper A decrease in diameter from one to another place as taper in a
cylinder, taper of a shaft.
TOC Top dead center, which see.
Tel Tetraethyllead, which see.
Temperature indicator A gauge that indicates to the driver the temperature of the coolant in the cooling system, thus giving warning
of impending damage if the temperature goes too high.
Tetraethyllead A chemical put into engine fuel which increases octane
rating, or reduces knock tendency.
Thermal efficiency Relationship between the power output and the energy in the fuel burned to produce the output.
Thermostat A device that operates on temperature changes. Several
thermostats are used in engines. There is one in the cooling system,
another in the manifold heat control, etc.
Thermosiphon cooling Cooling by natural circulation of water, resulting
from fact that a given volume of hot water is lighter than an identical volume of cold water.
Throttle cracker Linkage from the starting motor switch to the throttle,
which opens the throttle slightly when the engine is being cranked.
Throttle-return check A device on the carburetor that prevents excessively sudden closing of the throttle.
Throttle valve The round disk in the lower part of the carburetor air
horn that can be turned to admit more or less air.
Timing In the engine, refers to timing of valves and also timing of
ignition.
Top dead center The piston position at which the piston has moved
to the top of the cylinder and the center line of the connecting
rod is parallel to the cylinder walls.
Torque Turning or twisting effort, measured in pound-feet.
Torque wrench A special wrench with a dial that indicates the amount
of torque being applied to a nut or bolt.
Trouble-shooting The detective work necessary to run down the cause
of a trouble; implies the correction of the trouble by elimination
of cause.
Stroke
[415]
Automotive Fuel, Lubricating, and Cooling Systems
One type of radiator core, consisting of tubes
to which cooling fins are attached; water flows through the tubes
between the upper and lower radiator tanks.
Turbulence In the engine, the rapid swirling motion imparted to the
air-fuel mixture entering the cylinder.
Two-barrel carburetor A dual carburetor, which see.
Two cycle Short for two-stroke cycle, which see.
Two-stroke cycle The series of events taking place in a two-stroke-cycle
engine, which are intake, compression, power, and exhaust, all of
which take place in two piston strokes.
Unbalanced carburetor Carburetor in which the float bowl is vented
into the open air, as opposed to a balanced carburetor, which see.
Updraft carburetor Carburetor in which air horn and other parts are
so arranged that the air passes up through the air horn on its way
to the intake manifold. Used on engines where there is not enough
headroom for a downdraft carburetor.
Vacuum An absence of air or other substance.
Vacuum gauge In automotive-engine service, a device that measures
intake-manifold vacuum and thereby indicates actions of engine
components.
Valve A device that can be opened or closed to allow or stop the flow
of a liquid, gas, or vapor from one place to another.
Valve clearance The clearance between the adjusting screw on the
valve lifter and the valve stem (in L-head engines) or between the
rocker arm and the valve stem (in I -head engines).
Valve lifter Also called valve tappet. The cylindrical part of the engine
that rests on a cam of the camshaft and is lifted by the cam action
so that the valve is opened. There is a valve lifter for each valve.
Vapor lock A condition in the fuel system, in which gasoline has
vaporized, as in the fuel line, so that fuel delivery to the carburetor
is blocked or retarded.
Vent An opening from an enclosed chamber, through which air cap
pass.
Venturi In the carburetor, the constriction in the air horn that produces
the vacuum responsible for the movement of gasoline into the passing air.
Vibration A complete rapid motion back and forth; oscillation.
Viscosity The term used to describe a liquid's resistance to flow. A thick
oil has greater viscosity than a thin oil.
Viscous Thit;k, tending to resist flOWing.
Viscous friction Friction between layers of a liquid.
Vise A gripping device for holding a piece while it is being worked on.
[416]
,
Tube-and-fin radiator core
Appendix B: Glossary
Volatility A measurement of the ease with which a liquid vaporizes.
Volumetric efficiency Ratio between amount of air-fuel mixture that
actually enters an engine cylinder to the amount that could enter
under ideal conditions.
Water-distributing tube In the engine cooling system, a tube that improves water circulation around exhaust valves and other areas
that might overheat.
Water jacket The space between the inner and outer shells of the
cylinder block or head, through which cooling water can circulate.
Water pump In the cooling system, the device that maintains circulation
of the water between the engine water jackets and the radiator.
Water sludge A black, viscous substance that forms in the engine
crankcase due to water's collecting and being whipped into the oil
by the crankshaft.
Work Work is the changing of the position of a body against an
opposing force, measured in foot-pounds.
[417]
Index
Accelerator-pump circuit, 84--87
Air bleed, 100, 101
Air cleaner, 51-53
servicing of, 212
Air-cooled engines, 355, 356
Air-fuel ratios, 67, 68
Antifreeze solutions, 370, 371
testing of, 381, 382
Antifriction bearings, 298
Anti-icing in carburetor, 97,98
Antipercolator, 100
Atmospheric pressure, 37, 38
Atomization, 55
Atoms, 29-32
Backfiring of engine, 205
Ball bearings, 298
Bearings, 294-298
Body of oil, 301, 302
Borderline knock test, 169, 170
Borderline lubrication, 292
Buick carburetors, overhaul of, 258267, 276-289
Bypass oil filter, 323
Carburetors, 54-61, 67-140,239-289
accelerator pump in, 84-87
adjustments of, 241-246
air bleed in, 100, 101
antipercolator in, 100
checks of, 205, 206
choke in, 87, 94,213-217
circuits in, 68-94
compensating system in, 101-103
dual type of, 124-126
float-bowl vent in, 71, 72
float circuit in, 68-72
four-barrel type of, 126-134
fundamentals of, 45-61, 67-103
installation of, 289
Carburetors, removal of, 246
repair of, 239-289
servicing of, 239-289
troubles in, 239-241
Cetane number, 177, 178
CFR Uniontown road test, 169
Change of state, 35
Chassis dynamometers, 190
Chevrolet carburetors, overhauling of,
249-255
Chevrolet oil-pump service, 346, 347
Chevrolet water-pump service, 389391
Choke, 87-94
adjustment of, 213-216
servicing of, 216, 217
Circuits in carburetor, 68-94
Combustion, 33, 34, 176
Combustion analyzers, 186, 187
Compensating system, 101-103
Compression ratio, 163, 164
Cooling systems, engine (see Engine
cooling systems)
Crankcase ventilation, 328-330
Detergents in oil, 303, 304
Detonation, 171, 172
DC oil, 309
Diesel engines, 145-154
fuels for, 176-179
Dry friction, 291, 292
DS oil, 309
Dual carburetors, 124-126
overhaul of, 258-267
Dynamometers, 190
Elements, 29, 30
Engine, 3-25
diesel type of, 145-154
operation of, 4-12
[419}
Automotive Fuel, Lubricating, and Cooling Systems
Engine cooling systems, 354-395
air-cooled type of, 355, 356
care of, 382
cleaning of, 383-388
flushing of, 383-388
forced circulation in, 357
liquid-cooled type of, 356-360
purpose of, 354, 3.55
servicing of, 376-395
testing of, 376-383
trouble-shooting of, 382, 383
Engine fan, 361, 362
Engine lubricating system, 291-.'351
checks of, 336-340
combination splash and pressure,
315-317
pressure feed, 313, 314
purpose of, 299, 300
servicing of, 335-351
splash feed, 313, 314
trouble-shooting of, 337-340
types of, 313-317
Evaporation, 55
Exhaust-gas analyzers, 186, 187
Exhaust svstem, 61, 62
dual, 63
Expansion due to heat, 36
Fan, engine, 361, 362
Fast idle, 99, 100
Float bowl, 59-61
vents in, 71, 72
Float circuits, 68-72
Fluiditv of oil, 301, 302
Flywheel, 14
Ford carburetors, 134-140
overhaul of, 267-276
Ford oil-pump service, 349-351
Ford water-pump service, 394, 395
Four-barrel carburetor, 126-134
overhaul of, 276-289
Friction, 291-294
Friction bearings, 295-298
Fuel filters, 42
Fuel gauge, 42-44
servicing of, 220, 221
Fuel-injection System, 145-150
Fuel-line service, 218-220
Fuel-mileage testers, 185, 186
""'uel-nozzle action, 58
._
,
420]
.
.
Fuel pump, 44-51, 187-189, 225-235
electric, 50, 51
inspection of, 222, 223
installation of, 235
removal of, 225
servicing of, 225-235
testers for, 187-189
troubles in, 223, 224
Fuel systems, 28-289
diesel type of, 147-154
operation of, 41-63
servicing of, 211-289
troubles in, 184-206
Fuel tank, 41, 42
servicing of, 217, 218
Full-flow oil filter, 323-325
Full-power circuit, 80-83
Gasoline, 159-176
antiknock value of, 167-175
octane rating of, 167-175
origin of, 159, 160
volatility of, 160-163
Governor: 112-115
Greases, 311-313
Greasy friction, 292
Heat, 34, 35
of compression, 164
Heater, car, 365, 366
High-speed circuits, 77-83
Idling circuits, 72-77
Ignition system, 18-25
advance mechanisms in, 20-25
controls of, 107-109
Intake manifold, 53, 54
Knocking, cause of, 165-7~
control of, 172-175
Liquefied petroleum gas, 154-156,
179,180
Low-speed circuits, 72-77
LPG (see Liquefied petroleum gas)
Lubricants, automotive, 311-313
Lubricating systems, engine (see Engine lubricating systems)
Lubrication, theory of, 293, 294
Manifold heat control, 94-97
in V-8, 96, 97
Missing of engine, 205
. ... ":::.:.
'
lrulex
ML oil, 308
MM oil, 308
Molecules, 32, 33
MS oil, 308
Muffier, 62, 63
Relief valve in lubricating system,
320-322
servicing of, 344
Rings, piston, 12, 13
Roller bearings, 298
Octane, 167-175
Oil, changing of, 309, 310, 340-342
consumption of, 310, 311
function of, 299, 300
properties of, 301, 305
service ratings of, 30S, 309
sources of, 300, 301
viscosity of, 301, 302
Oil coolers, 325, 326
Oil filter, 322-325
servicing of, 344-345
Oil-level indicators, 330
Oil pan, 313-318
servicing of, 342-344
Oil-pressure indicators, 326-328
servicing of, 351
Oil pumps, 318-320
servicing of, 345-351
Sludge, crankcase, 306-30S
Stalling of engine, 204, 205
Starting-control switches, 109,
no
Tachometers, lS9, 190
Temperature indicators, 371-373
Thermosiphon cooling system 356
357
'
,
Thermostat in cooling system, 366368
testing of, 377
Throttle cracker, 98, 99
Throttle-return checks, 110-112
Throttle valve, 5S, 59
Two-barrel carburetors, 124-126
overhaul of, 258-267
Updraft carburetors, 116-122
Quadrijet carburetor, 126-134
overhaul of, 258-261, 216-289
Vacuum, 38
Vacuum gauges, 189
Vacuum pump, 48-50
Valves, engine, 7-9
arrangements of, 16-18
Vapor lock, 202
Vapor-pressure temperature indicator,
371, 372
Venturi, 56-58, 78
VI (viscosity index), 304, 305
Viscosity, 292, 293, 301, 302
Viscosity index, 304, 305
Viscous friction, 292, 293
Volatility, 160
Radiator, 363-365
flushing of, 386, 3S7
repairing of, 388, 389
testing of, 377, 378
Radiator pressure cap, 368-370
Water-distributing tubes, 358-360
Water jackets, engine, 358--360
Water pumps, 360
servicing of, 389-395
testing of, 378
Piston rings, lZ, 13
Plymouth carburetors, overhaul of,
255-258
Plymouth oil-pump service, 347-349
Plymouth water-pump service, 391394
Preignition, 171, 172
Pressure, gas, 36, 37
Pressure tester for lubricating system,
33.5, 336
[421]
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