GMC 1976 ZEO 6083 Maintenance Manual page 311

6A- 4 6 ENGINE
Figure 46-Measuring Piston
The piston and cylinder bore must be free of oil
and at the same temperature.
NOTE :
In some engines, oversize pistons may be
found . These pistons will be .010" oversize .
1 . Place a strip of .0015" feeler gauge against the
upper side of the bore, at 90° to the normal piston pin
location . Attach a scale which measures in pounds to
a feeler gauge . See Figure 42 .
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 3 to 12 pounds while pulling the feeler
gauge out of the bore .
Figure 47-Checking Piston Clearance
Each piston should be fitted to its individual cyl-
inder and marked for that cylinder .
CLEANING PISTON
PISTON INFORMATION CHART
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 .
BORE
DIAMETER
CYLINDER
BORE
SELECTION
BORE
SIZES
PISTON
SELECTION
PISTON
SIZE
PISTON
DIAMETER
PISTON TO
CYL . BORE
CLEARANCE
RING
SIZE
A
4 .1250-4 .1255 A 4.1240-4.1235
4 .1250-4 .1270
B 4 .1255-4 .1260
B 4.1245-4 .1240 4 .1255-4 .1235
Std .
Std . C
4.1260-4 .1265
C
4.1250-4.1245 Std .
D
4 .1265-4 .1270 D 4 .1255-4.1250
1
4 .1350-4 .1355
1
4.1340-4.1335
.001 to .002
4 .1350-4 .1370 K 4 .1355-4 .1360 K 4.134511.1340 4 .1355-4 .1355
.010 " O .S .
.0100 .S. L
4 .1360-4 .1365 L 4.1350-4.1345 .0100 .S .
M 4 .1365-4 .1370 M 4.1355-4.1350