Pontiac FIREBIRD 1972 Service Manual page 602

6-90 1972 PONTIAC SERVICE MANUAL
SIZING POINT
Fig. 6-1 5 8 Piston Sizing Points
FIT AND REPLACE PISTON
Pistons should be fitted in the bores by actually measuring
the fit. Clearance between the piston and the cylinder bore
should be .0025" to .0033" (all except 307 engine) or
,0005" to .0011" (307 engine).
If cylinder bores have been reconditioned, o r 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 to 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. If any or all of
the parts are hotter or colder than normal room
temperature, improper fitting will result.
Measure the piston skirt perpendicular to the piston pin
Fig. 6-1 59 Measuring Piston
Fig. 6 - 1 6 0 Cylinder Bore and Piston Identification
boss (piston pin removed) and at sizing point indicated in
Fig. 6-158.
Make sure the micrometer is in full contact (Fig. 6-159).
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",
.010" 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 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" (all
except 307 engine) or .00015" to .00025" (307 engine)
loose with pin and bosses clean and dry.