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6A2-20
1977 PONTIAC SERVICE MANUAL
Fig. 6A2-45 Piston Pin Replacement
Fig. 6A2-46 Connecting Rod Identification
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 PIN
Fit
Piston pins normally do not become loose enough to
cause a knock or tapping until after very high mileage and
in such cases the piston and rod can be reamed and oversize
pins installed.
The piston pin fit in the piston is .0002" to .0004" loose
with pin and bosses clean and dry.
Piston and pin must be at room temperature when
checking fit and pin must be able to e l l from piston by its
own weight.
CYLINDER BORES
Inspect
Inspect cylinder bores for out-of-round or excessive
taper, with an accurate cylinder gage 5-8087 or comparable,
at top, middle and bottom of bore. (Fig. 6A2-47). Measure
cylinder bore parallel and at right angles to the centerline of
the engine to determine out-of-round. Variation in measure
from top to bottom of cylinder indicates the taper in the
cylinder. Fig. 6A2-48 illustrates area in cylinder where
normal wear occurs. If dimension "A" is larger than
dimension "B" by .003", it indicates the necessity of cylinder
boring and installing new rings and pistons. Cylinder bores
can be measured by setting the cylinder gage dial at zero in
the cylinder at the point of desired measurement. Lock dial
indicator at zero before removing from cylinder, and measure
across the gage contact points with outside micrometer, with
the gage at the same zero setting when removed from the
cylinder (Fig. 6A2-49).
1
Fig. 6A2-47 Measuring Cylinder Bore (Typical)
Fine vertical scratches made by ring ends will not by
themselves cause excessive oil consumption, therefore,
honing to remove them is unnecessary.
Honing or Boring
Ifa piston other than standard size is to be installed, the
cylinder should be bored, rather than honed, to effect a true
bore.
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