Pontiac tempest 1968 - Piston Fit and Replace; Piston Rings - Replace

6-30
1968 PONTIAC SERVICE MANUAL
all traces of abrasive. If all traces of abrasive are
not removed, rapid wear of new rings and piston will
result.
Intermixing different size pistons has no effect on
engine balance as all Pontiac pistons from standard
size, up to .030" oversize, weigh exactly the same.
Pontiac does not recommend boring beyond .010"
during warranty period so that if necessary, engine
can be serviced at high mileage without cylinder
block replacement.
PISTON-FIT AND REPLACE
Pistons should be fitted in bores by actually meas-
uring fit. Clearance between the piston and the cylin-
der bore should be .0022" to .0028".
If cylinder bores have been reconditioned or if
pistons are being replaced, reconditioning of bores
and fitting of pistons should be closely coordinated.
If bore has been honed, it should be washed thor-
oughly with hot, soapy water and stiff bristle brush.
Using a cylinder checking gauge, measure the cyl-
inder bore crosswise of block to find smallest
diameter. Record smallest diameter of each bore.
NOTE: When measuring cylinder bores and pis-
tons, it is very important that block and pistons
be at room temperature. If any or all parts are
hotter or colder than normal room temperature,
improper fitting will result.
Measure piston skirt perpendicular to piston pin
boss (piston pin removed) at sizing point indicated
in Fig. 6-59.
Make sure the micrometer is in full contact.
As pistons are measured they should be marked
for size identification and measurements recorded.
If there is excessive clearance between a cylinder
bore and piston which was installed in that bore, a
new piston should be used.
New pistons are serviced in standard size and
.001", .002", .005", .010", .020" and .030" oversize.
NOTE: Since these are nominal or basic sizes, it
is important that new pistons be measured to en-
sure proper fit. All new pistons are serviced with
selectively fitted piston pins.
After all measurements have been made, match
new pistons with cylinders where they will fit with
proper clearance. Honing cylinder bore may be nec-
essary to effect a proper fit. When properly mated,
mark pistons with cylinder numbers they fit so they
will not become mixed.
CONNECTING ROD TO PISTON-ASSEMBLE
There is a notch cast in top of all piston heads to
facilitate proper installation. The piston assemblies
should always be installed with notch toward front of
engine.
1. Lubricate piston pin holes in piston and con-
necting rod lightly with graphite lubricant.
2. Position connecting rod in its respective piston
so that oil squirt hole faces toward distributor side
of engine. Fig. 6-60.
3. Install piston pin on installer and pilot spring
and pilot (J 9510-4) in support (Fig. 6-61). Use
piston pin removing and installing tool J 9510.
4. Install piston and rod on support, indexing pilot
through piston and rod.
5. Place support on arbor press, start pin into
position and press on installer until pin pilot bottoms.
6. Remove installer and support assembly from
piston and connecting rod assembly.
7. Check piston pin for freedom of movement in
piston bore.
PISTON RINGS-REPLACE
1. Remove connecting rod and piston assembly
Fig. 6-60 Piston and Rod Assembly