Pontiac FIREBIRD 1972 Service Manual page 552

1972 PONTIAC SERVICE MANUAL
PISTON
FIT A N D REPLACE
Pistons should be fitted in the bores by actually measuring
the fit (measure O.D. of piston at sizing point and I.D. of
cylinder bore). Clearance between the piston and the cyl-
inder bore should be .0005" to .0015".
-
If cylinder bores have been reconditioned, or if pistons are
being replaced, reconditioning of bores and fitting of pis-
tons should be closely coordinated.
If bore has been honed, it should be washed thoroughly
with hot, soapy water and a stiff bristle brush.
Using a cylinder checking gauge, measure the cylinder
bore crosswise of the block to find the smallest diameter.
Record the smallest diameter of each bore.
CAUTION:
When measuring cylinder bores and
pistons, it is very important that the block and
pistons be at room temperature. Ifany or all of
the parts are hotter or colder than nonnalroom
temperature, improper fitting will result.
Measure the piston skirt perpendicular to the piston pin
boss (piston pin removed) and at the sizing point indicated
in Fig. 6-65.
Make sure the micrometer is in full contact.
As the pistons are measured they should be marked for
size identification and the measurements recorded.
If there is excessive clearance between a cylinder bore and
the piston which was installed in that bore, a new piston
should be used.
New pistons are serviced in standard size and .005", .010",
.020" and .030" oversize.
Since these are nominal or basic sizes, it is important that
new pistons be measured to ensure proper fit. All new
pistons are serviced with selectively fitted piston pins.
After all measurements have been made, match the new
pistons with the cylinders where they will fit with proper
clearance. Honing of cylinder bore may be necessary to
effect a proper fit. When properly mated, mark the pistons
with the cylinder numbers they fit so they will not become
mixed.
CONNECTING ROD TO PISTON
ASSEMBLE
There is a notch cast in the top of all piston heads to
facilitate proper installation. The piston assemblies should
always be installed with the notch toward the front of the
engine.
Lubricate piston pin holes in piston and connecting
rod lightly with graphite lubricant.
Position connecting rod in its respective piston so
that flange or heavy side of rod at bearing end will be
toward front of engine (cast slot in piston top).
Install piston pin on installer and pilot spring and
pilot in support (Fig. 6-66). Use piston pin removing
and installing tool J-95 10.
Install piston and rod on support, indexing pilot
through piston and rod.
Place support on arbor press, start pin into position
and press on installer until pin pilot bottoms.
Remove installer and support assembly from piston
and connecting rod assembly.
Check piston pin for freedom of movement in piston
bore.
I
PISTON
PIN
REMOVER A N D
INSTALLER
Fig. 6 - 6 5 Measuring Piston Fig, 6-66 Piston Pin Replacement