Assemble Connecting Rod To Piston; Replace Piston Pin; Fitting Pin In Piston - Pontiac Grand Prix Service Manual

6-68 1969
PONTIAC SERVICB MANUAL
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.
NOTE: When measuring cylinder bores and pistons, it is
very important that the block and pistons be at room
temperature. v a n y or all of the parts are hotter or colder
than nonnal room temperature, improper fitting will
result.
Measure the piston skirt perpendicular to the piston
pin boss (piston pin removed) and at sizing point
indicated in Fig. 6-120.
Make sure the micrometer is in full contact (Fig.
6-121).
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 .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 ensure proper
fit. All new pistons are serviced with selectively jtted
piston pins.
After all measurements have been made, match the
new pistons with cylinders where they will fit with
proper clearance. Honing of cylinder bore may be
necessary to effect a proper fit. When properly mated,
mark pistons with cylinder numbers they fit so they
will not become mixed.
FITTING PIN IN PISTON
The piston pin fit in the piston is .0005" to .0007"
loose with pin and bosses clean and dry.
NOTE: Piston and pin must be at room temperature
when checking fit and pin must be able to fall fiom
piston by its own weight.
FIl'TING OVERSIZE PINS IN PISTONS AND
CONNECTING ROD PIN BORES
In case the standard size piston pin does not fit
properly in the piston, an oversize piston pin must be
fitted. Piston pins are available in .001" and .003"
oversize.
When oversize pins are used, the piston pin bosses
must be honed to give required fit. It will also be
necessary to hone the connecting rod pin bore to fit
the oversize pin, using a Sunnen hone or similar
accurate equipment.
NOTE: A special grit hone is used for honing the
connecting rod pin bore. The piston pin size should be
.0008' to
.0016"
larger than connecting rod pin bore for
proper press fit. The piston pin should not show any
movement under 1500 lb. minimum load ajer assembly
in rod:
ASSEMBLE CONNECTI~G ROD TO PISTON
There is a notch cast in the top of all piston heads to
facilitate proper installation. The piston assemblies
should always be installed with notch toward front of
engine. Position rod in piston so that oil squirt hole
(Fig. 6-122) is toward camshaft.
REPLACE PISTON PIN
1. Place pilot plunger and spring in the support base to
be used as a pilot end stop. See Fig. 6-123 insert for
correct base support and pilot plunger for type pistons
being serviced.
2. Place pilot plunger of tool J 6901 in piston pin bore
and place on arbor press.
Fig. 6-122 Piston and Rod Assembly