Pontiac FIREBIRD 1972 Service Manual page 601

V-8
ENGINE 6-89
Fig. 6-155 Normal Cylinder Wear Pattern
Fig. 6-155 illustrates area in cylinder where normal wear
occurs. Cylinder bore can be measured (Fig. 6-156) by
setting cylinder gauge dial at zero in cylinder at the point
of desired measurement. Lock dial indicator at zero before
removing from cylinder, and measure across the gauge
contact points with outside micrometer with gauge at the
same zero setting when removed from cylinder (Fig. 6-
157).
Take several measurements parallel and at right angles to
the crankshaft, between 1/2" and 4" from the top of the
cylinder. Subtract the smallest measurement found from
the largest. If this figure exceeds .0006" (all except 307
engine) or .001lV (307 engine), a piston cannot be fitted
properly, and the cylinder must be honed. New rings and
a new oversized piston must then be fitted.
Fine vertical scratches made by ring ends will not cause
excessive oil consumption, therefore, honing to remove
these scratches is unnecessary.
Fig. 6-156 Measuring Cylinder Bore
Fig. 6-157 Meaduring Cylinder Gauge
HONING OR BORING
If a piston other than standard is to be installed, the
cylinder should be bored, rather than honed, to effect a
true bore.
To eliminate the possibility of honing taper into the cylin-
der, full strokes of the hone should be made in addition
to checking measurement at top, middle and bottom of
bore repeatedly.
Always be sure the crankshaft is out of way of boring
cutter when boring each cylinder. Crankshaft bearings
and other internal parts must be covered or taped to pro-
tect them during boring or honing operation. When taking
final cut with a boring bar, leave .001" on the diameter for
finish honing to give required piston-to-cylinder clearance
specifications. (Honing or boring operation must be done
under close suvervision so that siecified clearance be-
tween pistons, rings, and cylinder bores is maintained).
By measuring the piston to be installed at the sizing points
(Fig. 6- 158) and adding the mean of the clearance specifi-
cation, the finish hone cylinder measurement can be deter-
mined. It is important that both block and piston be
measured at normal room temperature, 60"
-
90
O F .
After final honing and before the piston is checked for fit,
each cylinder bore must be thoroughly cleaned. Use soapy
water solution and wipe dry to remove all traces of abra-
sive. If all traces OT 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 pistons from standard size up to .03OV over-
size 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.