Pontiac tempest 1968 Service Manual page 340

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. 1 2 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