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6A4-26
1977 PONTIAC SERVICE MANUAL
Fig.
6A4-68
Cylinder Bore Marking
r
MEASURE
314" BELOW CENTERLINE
F PISTON P I N HOE FOR
3
ND 403 C.
I. D. ENGINES.
3668
Fig.
6A4-69
Measuring Piston
1. Place a strip of .0015" feeler aauae against the uvver
- - -
side of the bore, at 90" to the normal piston pin locaiion.
Attach Scale 5-5515 to feeler gauge. (Fig. 6A4-70)
2. Insert piston upside down with pin and rings removed,
into bore.
3. While holding the piston in the center of its normal
travel, slowly pull the scale in a straight line and note the
reading on the scale. The reading should be between between
3 to 12 pounds while pulling the feeler gauge out of the bore.
Each piston should be fitted to its individual cylinder
and marked for that cylinder.
CHECKING CYLINDER BORE
NOTE: Refer to PISTON INFORMATION Chart.
Cylinder bore size can be measured with inside
micrometers or a cylinder gauge. Maximum allowable taper
of the cylinder bore is .OOln. The most wear will occur at the
top of the ring travel.
Fig.
6A4-70
Checking Piston Clearance
Reconditioned cylinder bores should be held to not more
:han .OOln out-of-round and .OOlm taper.
If the cylinder bores are smooth, the cylinder walls
should not be deglazed. If the cylinder walls a;e scored, the
walls may have to be honed before installing new rings. It is
important that reconditioned cylinder bores be thoroughly
washed with a soap and water solution to remove all traces
of abrasive material to eliminate premature wear.
CLEANING PISTON
Clean the pistons by scraping carbon off the top of the
piston. Deposits in the ring grooves should be removed with
a suitable ring groove cleaning tool. It is important that the
ring grooves be completely free of deposits.
PISTON RINGS
The pistons have three rings (two compression rings and
one oil ring). The oil ring consists of two rails and an
expander.
Ring Tolerances
When installing new rings, ring gap and side clearance
should be checked as follows:
Piston Ring and Rail Gap
Each ring and rail gap must be measured with the ring
or rail positioned squarely and at the bottom of the ring-travel
area of the bore. (Fig. 6A4-72)
The end gap measurement should be .013" to .023" for
compression rings and .015" to .055" for oil rings.
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