Normal Cylinder Wear Pattern; Piston Sizing Points; Measuring Cylinder Gauge; Piston Fit And Replace - Pontiac Grand Prix Service Manual

SIX CYLINDER ENGINE 6 -29
Fig.
6-57
Normal Cylinder Wear Pattern
When boring, always be sure crankshaft is out of way
of boring cutter when boring each cylinder. Crankshaft
bearings and other internal parts must be covered or
taped to protect them during d 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.
NOTE: Honing or boring operation must be done under
close supervision so that specified clearnace between
pistons, rings, and cylinder bores is maintained.
By measuring the piston to be installed at sizing points
(Fig. 6-59) and adding the means of clearance
specification, the finish hone cylinder measurement
can be determined. It is important that both block and
piston be measured at normal room temperature,
60"90"F.
After fmal honing and before piston is checked for fit,
each cylinder bore must be thoroughly cleaned. Use
Fig. 6-58 Measuring Cylinder Gauge
Fig. 6-59 Piston Sizing Points
soapy water solution and wipe dry to remove all traces
of abrasive. If all traces of 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 Pontiac pistons from standard
size, up to .030" oversize, 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.
PISTON-FIT AND REPLACE
Pistons should be fitted in bores by actually measuring
fit. Clearance between the piston and the cylinder bore
should be .0022" to .0028".
If cylinder bores have been reconditioned or if pistons
are being replaced, reconditioning of bores and fitting
of pistons should be closely coordinated.
If bore has been honed, it should be washed thor-
oughly with hot, soapy water and stiff bristle brush.
Using a cylinder checking gauge, measure the cylinder
bore crosswise of block to find smallest diameter.
Record smallest diameter of each bore.
NOTE: When measuring cylinder bores and pistons, it is
very important that block and pistons be at room
temperature.
I f
any or all parts are hotter or colder than
normal room temperature, improper fitting will result.
Measure piston skirt perpendicular to piston pin boss
(piston pin removed) at sizing point indicated in Fig.
6-59.
Make sure the micrometer is in full contact.