GMC 1990 Light Truck Repair Manual page 359

Figure 8—Measuring Piston Pin Diameter
CLEANING AND INSPECTION
Pjyi 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
L*
— 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)
Measure (Figures 8 and 9)
m
1. Piston pin diameter
" Specifications."
2. Piston pin to piston clearance.
• Measure the piston pin hole diameter (figure
9).
• Subtract the piston pin diameter from the
piston pin hole diam eter to obtain the
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)
a y
Clean
Piston pin and bushing. The parts must be free of oil
and dirt.
GENERAL ENGINE MECHANICAL 6A-7
B-04981
8
(figure ). Check against
Measure (Figures 8 and 10)
1. Piston pin diameter (figure
" Specifications."
2. Piston pin bushing ID. Use an inside micrometer
10
(figure ).
3. Piston pin to bushing clearance. Subtract the piston
pin diameter from the piston pin bushing 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
8
). Check against
B-04985