6C-1
ENGINE
TUNE-UP
TUNE-UP
SEQUENCE
INDEX
SUBJECT PAGE
Spark
Plugs—Removal . . 6C-1
Compression Test „ 6C-1
Spark
Plugs—Clean-Test-Install 6C-2
Ignition System—Service and Repairs . . . . 6C-2
Battery and Battery Cables—Clean
and
Test . 6C-3
Generator
and Regulator . . . . . 6C-3
Fan
Belt—Inspect and Adjust 6C-3
Manifold Heat Valve—Check Operation . . . 6C-3
Check
Intake Manifold Bolts . . 6C-3
Air
Cleaner—Service . . . 6C-4
SUBJECT PAGE
Fuel
Lines and Filter—Inspect and Service. 6C-4
Coolant
Level
and Hoses—Check 6C-4
Crankcase
Oil Level—Check , . . 6C-4
Choke
Adjustment 6C-4
Idle
Stop Solenoid 6C-4
Connect Tune-Up Equipment 6C-4
Ignition Point Dwell . 6C-4
Ignition Timing and Advance . 6C-5
Idle
Speed and Mixture Adjustment 6C-5
Crankcase
Ventilation ............ 6C-5
Road
Test 6C-5
INTRODUCTION
Engine
tune-up is diagnosis and preventive main-
tenance performed at regular intervals to restore
maximum performance and
economy
in an
engine.
It
is advisable to
follow
a
definite
and thorough
procedure of analysis and correction as
suggested
by the
sequence-index
above.
A
quality tune-up is recommended every 12 months
or
12,000 miles in order to assure proper engine
performance
and complete effectiveness of exhaust
emission
systems.
SPARK
PLUG REMOVAL
Remove any foreign matter from around spark
plugs
by blowing out with compressed air, then
disconnect wires and remove plugs.
COMPRESSION
TEST
Test
compression with
engine
warm, all spark
plugs
removed and throttle and choke wide open.
Crank
engine
through at least five compression
strokes to obtain
highest
possible
reading. No
cyl-
inder should be
less
than 80% of the
highest
cylinder
(see examples). Excessive variation
between
cyl-
inders, accompanied by low
speed
missing of the
cylinder or cylinders which are low, usually indi-
cates
a valve not properly seating, a burned valve or
broken piston ring. Low pressures,
even
though
uniform, may indicate worn rings. This will usually
be accompanied by
excessive
oil consumption. I
NOTE:
Low compression pressures on ram air,
400 H.O. or 428 H.O. engines are not a
valid
indi-
cation
of engine condition. Due to the long valve
overlap
period with camshafts used in these en-
gines
compression readings (at cranking speeds)
as
low as 120 psi are considered normal.
6
CYL.
Example
1
Cyl.
12 3 • 4 5 6
Press.
129 127 130 121 116 102
80% of 130 (highest) is 104. Thus cylinder No. 6
is
less
than 80% of No. 3. This condition, accom-
panied by low
speed
missing, indicates a burned
valve or broken piston ring.
Example
2
Cyl.
1 2 3 4 5 6
Press.
85 96 90 87 85 91
80% of 96 is 77. While all cylinders are well
above
77,
they
are all excessively low. This indi-
cates
all poor valves or, if accompanied by oil con-
sumption, worn rings or low crank speed.
If
compression is subnormal, tune-up will probably
not be satisfactory.
V-8
Example
1
Cyl.
1 2 3 4 5 6 7 8
Press.
136 138 135 144 102 137 140 141
80% of 144 (highest) is 115. Thus cylinder No. 5 is
less
than 80% of No. 4. This condition, accompanied
by low
speed
missing, indicates a burned valve or
broken piston ring.
Example
2
Cyl.
1 2 3 4 5 6 7 8
Press.
85 91 90 87 96 93 87 89
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