GMC T Series 1994 Repair Manual page 336

1 G AG ING POINT
2. Piston pin for:
a. Scoring.
b. Galling caused by improper installation.
c. Fit in connecting rod and piston.
3. Piston for:
a. Scoring of the skirt.
b. Cracks.
c. Broken ring lands.
d. Wear.
PISTON FITTING
Tool Required:
J 8087 Cylinder Bore Gage
[Y ] important
• When fitting pistons, both piston and cylinder
bore condition must be considered together.
Production and service pistons of standard and
(standard hi-limit) size have the same nominal
weight and can be intermixed individually without
affecting engine balance. Service pistons of
0.5 and 1 mm (0.0196 and 0.0393 in.) O.S. are
heavier and must be serviced in sets of four. If
necessary, used pistons may be fitted selectively to
any cylinder of the engine, providing they are in
good condition.
• Do not cut oversize pistons down or engine
balance will be affected.
Measure
m
1. Piston to cylinder bore clearance as follows:
a. Measure the cylinder bore diameter using
J 8087 or equivalent, refer to Figures 24
and 25.
b. M easure the piston diam eter, refer to
Figure 24.
c. Subtract piston diameter from cylinder bore
diameter to
clearance.
d. Compare piston-to-bore clearance obtained,
with those specified,
Specifications" in this section.
Figure 24 - Piston to Cylinder Bore Gaging Points
determine piston-to-bore
refer to " Engine
Figure 25 - Measuring Cylinder Bore
2. If used piston is not acceptable, check service
piston sizes and determine if a new piston can be
selected.
3. If cylinder bore must be reconditioned, measure
new piston diameter then hone cylinder bore to
obtain preferable clearance.
4. Select new piston and mark piston to identify the
cylinder for which it was fitted.
Clean
• Scrub the cylinder bore and the piston with soap
and water and remove all foreign material. Dry
and rub in clean engine oil.
PISTON RING FITTING
1. Select a set of new piston rings.
2. Measure piston ring end gap. Refer to Figure 26.
- Place piston into the cylinder at the bottom of
the ring travel.
- Place a piston ring on top of the piston.
- Back off the piston.
MC0500-6A2-L-EDS