Pontiac tempest 1968 Service Manual page 341

6 C - 2
1968 P O N T I A C SERVICE M A N U A L
80% of 96 Is 77. While a l l cylinders are well above
77, they are a l l excessively low. This indicates a l l
poor valves or, I f accompanied by o i l consumption,
worn rings or low crank speed. I f compression is
subnormal, tune-up w i l l probably not be satisfactory.
(See specifications at end of section 6 for correct
compression pressures.)
NOTE: The compression check is important be­
cause an engine with low or uneven compression
cannot be tuned successfully to give peak per­
formance. Therefore, it is essential that improper
compression be corrected before proceeding with
an engine tune-up.
CLEAN, TEST AND INSTALL SPARK PLUGS
1. Inspect each plug Individually for badly worn
electrodes, glazed, broken or blistered porcelains
and replace plugs where necessary. Refer to spark
plug diagnosis information presented i n Engine Elec­
t r i c a l for an analysis of plug conditions.
2. Clean serviceable spark plugs thoroughly, using
an abrasive-type cleaner. File the center electrode
flat.
3. Inspect each spark plug for make and heat
range. A l l plugs must be of the same make and
number or heat range. (See section 6E. for correct
spark plug usage.)
4. Adjust spark plug gaps to . 0 3 5 " using a round
feeler gauge.
CAUTION: Never bend the center electrode to
adjust gap. Always adjust by bending ground or
side electrode.
5. I f available, test plugs with a spark plug tester.
6. Inspect spark plug hole threads and clean be­
fore installing plugs. Corrosion deposits can be r e ­
moved with a 14 m m . x 1.25 SAE spark plug tap
(available through local jobbers) or by using a small
wire brush i n an electric d r i l l . Use plenty of grease
on tap to catch any chips.
CAUTION: Use extreme care when using tap to
prevent cross threading. Also crank engine several
times to blow out any material dislodged during
cleaning operation.
7. Install spark plugs to engine with new gaskets
and tighten to 25 l b . ft. torque.
Improper Installation is one of the greatest single
causes of unsatisfactory spark plug performance.
Improper installation is the result of one or more of
the following practices:
• Installation of plugs with insufficient torque to
fully seat the gasket.
• Installation of the plugs using excessive torque
which changes gap settings.
• Installation of plugs on dirty gasket seal.
• Installation of plugs to corroded spark plug hole
threads.
Failure to install plugs properly w i l l cause them to
operate at excessively high temperatures and result
in reduced operating life under m i l d operation or
complete destruction under severe operation where
the intense heat cannot be dissipated rapidly enough.
Always remove corrosion deposits i n hole threads
before installing plugs. When corrosion is present i n
threads, normal torque is not sufficient to compress
the plug gasket and early failure from overheating
w i l l result.
Always use a new gasket and wipe seats i n head
clean. The gasket must be fully compressed on clean
seats to complete heat transfer and provide a gas
tight seal i n the cylinder. For this reason as well as
the necessity of maintaining correct plug gap, the use
of correct torque Is extremely Important during
installation.
IGNITION SYSTEM SERVICE AND REPAIRS
1. Replace brittle or damaged spark plug wires.
Install a l l wires to proper spark plug. Proper posi­
tioning of spark plug wires i n supports is important
on V-8 engines to prevent cross-firing.
2. Tighten a l l Ignition system connections.
3. Replace or repair any wires that are frayed,
loose or damaged.
4. Remove distributor cap, clean cap and inspect
for cracks, carbon tracks and burned or corroded
terminals. Replace cap where necessary.
5. Clean rotor and Inspect for damage or deteri­
oration. Replace rotor where necessary.
6. Check the distributor centrifugal advance mech­
anism by turning the distributor rotor as far as
possible, then releasing the rotor to see i f the
springs return i t to its original position. If the
rotor does not return readily, the distributor must
be disassembled and the cause of the trouble
corrected.
7. Check to see that the vacuum advance control
operates freely by turning the movable breaker plate
to see i f the spring returns to its original position.
Any stiffness i n the operation of the spark control
w i l l affect the ignition timing. Correct any inter­
ference or binding condition noted.
8. Examine distributor points and clean or replace
if necessary.