GMC 1989 Light Duty Truck Repair Manual page 341

CLEANING AND INSPECTION
* 31
Clean
Piston.
— Remove all varnish and carbon deposits. DO
NOT USE A WIRE BRUSH.
— Remove the carbon from the ring grooves. Use
a ring groove cleaning tool.
— Oil control ring groove holes.
Inspect
I?
Piston pin bore in the piston and connecting rod.
Check for scuffing, burrs, etc.
Piston for scratches, wear, etc.
Connecting rod for cranks, nicks, etc. If a suitable jig
is available, check the connecting rod for a bent or
twisted condition.
Piston.
— Ring land for cracking, wear, etc.
— Ring grooves for burrs, nicks, etc.
— Skirts and pin bosses for cracking.
— Skirts for scuffing.
Connecting rod bearing inserts for scratches or
deep pitting.
MEASURING PISTON PIN TO PISTON
CLEARANCE (ALL EXCEPT 6.2 L)
M easure (Figures 8 and 9)
1. Piston pin d ia m e te r (figu re 8). C heck aga in st
" Specifications."
2. Piston pin to piston clearance.
• Measure the piston pin hole diameter (figure
9).
• Subtract the piston pin diam eter from the
p isto n pin h ole d ia m e te r to o b ta in th e
clearance.
• Replace the piston and piston pin if the
clearance exceeds specifications. The piston
and piston pin are a matched set and are not
available separately.
MEASURING PISTON PIN TO PISTON
PIN BUSHING CLEARANCE (6.2 L ENGINES)
Clean
Piston pin and bushing. The parts must be free of oil
and dirt.
GENERAL ENGINE MECHANICAL 6A-7
M easure (Figures 8 and 10)
Piston pin d ia m e te r (figu re 8). C heck a ga in st
" Specifications."
Piston pin bushing ID. Use an inside micrometer
(figure 10).
3 Piston pin to bushing clearance. Subtract the piston
.
pin d ia m e te r from the piston pin b ushing ID.
Compare with " Specifications." If the clearance is
excessive, try a new piston pin. If the clearance is
Figure 10— Measuring Piston Pin Bushing Inside
Diameter