GMC 1976 ZEO 6083 Maintenance Manual page 692

Figure 14-Piston Groove Cleaning
When cleaning the connecting rods in solvent,
include the rod bore . Blow out all passages with
compressed air.
INSPECTION
The following text contains inspection proce-
dures concerning pistons and connecting rods .
1. Piston Inspection :
a. Inspect the pistons for fractures at the ring
lands, skirts and pin bosses . Check for wear at the
ring lands using a new ring and feeler gauge as shown
in Figure 15 . Replace the piston when the side clear-
ance of the top compression ring reaches 0.008".
b. Replace pistons showing signs of scuffing,
scoring, worn ring lands, fractures or damage from
preignition . Excessive piston wear near the edge of
the top ring land indicates preignition .
Figure 15-Checking Ring Side Clearance
ONAN MOTOR GENERATOR 24C- 1 5
2. Connecting Rod Inspection
a. Replace connecting rod bolts or nuts with
damaged threads. Replace connecting rods with
deep nicks, signs of fractures, scored bores or bores
out of round more than 0.002" .
b. Use a new piston pin to check connecting
rod for wear . A push fit clearance is required and
varies from engine to engine . If a new piston pin falls
through a dry rod pin bore as a result of its own
weight, replace the rod.
REPAIR
1 . Fitting Pistons:
a. Proper piston tolerances must be main-
tained for satisfactory operation.
b. Measure the piston as shown in Figure 16
to be sure the total piston-to-cylinder clearance fol-
lows specifications .
2. Fitting Piston Rings:
a. Install the piston ring in the cylinder bore .
Invert the piston and push the ring to the end of ring
travel, about halfway into the bore, which trues the
ring end gap . Check the gap with a feeler gauge as
shown in Figure 17 .
b. The practice of filing ring ends to increase
the end gap is not recommended. If the ring end gap
does not meet specifications, check for the correct set
of rings and correct bore size . A cylinder bore that
is 0.001" undersize will reduce the end gap 0.003".
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MEASURE CLEARANCE HERE
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Figure 16-Measuring Diameter of Piston