GMC T Series 1994 Repair Manual page 532

A. 1 5 °K E Y S T 0 N E
C O M P R E S S IO N RING
B. REC TA NG ULAR
C O M P R E S S IO N RING
C. SPIRAL EXPAN DER
RING
D. O IL C O N T R O L RING
116. RING, SNAP
117. PIN, PISTON
118. RING, ASSEMBLY
Figure 35— Piston and Components
surface is very important from the standpoint of
simulating the surface texture that would result
from a good engine break in.
• The "valleys" left by the rough hone are necessary
for proper oil retention for cylinder lubrication.
• Move the hone up and down to produce an approx­
imately 45 degree crosshatch pattern. Honing trav­
el technique is important for adherence to diameter,
taper and roundness specifications.
• The following is the surface roughness specifica­
tion for cylinder bores.
RA (Minimum) = 0.40 Micro-meter (16 micro-inch)
RA (Maximum) = 0.90 Micro-meter (32 Micro-inch)
• Prepare the cylinder bores for use by cleaning with
a hot water and detergent wash to remove debris.
Apply clean engine oil to the bore after cleaning.
PISTON AND CONNECTING
ROD ASSEMBLIES
DISASSEMBLY
❖
Disassemble (Figure 35)
; Important
• The standard production 6.5L pistons are avail­
able in two grade sizes identified by a J and K
ink or metal stamped on the bottom or top of
the piston. To ensure that the piston is installed
in its original bore during reassembly, mark the
piston according to its bore. This step is neces­
sary if the piston is removed from the connect­
ing rod.
1. Piston rings.
2. Connecting rod bearing shells. If the shells are to
be reused, place them in a rack so they can be
installed in their original connecting rod and cap.
3. Piston pin retainer. Pry out with a small screwdriver
or scribe with a rounded end.
4. Piston pin.
• Slide the pin from the piston.
5. Piston from the connecting rod.
CLEANING AND INSPECTION
XJjji
• Piston.
I?
Piston pin bore in the piston and connecting rod.
3706r4862
Check for scuffing, etc.
Piston for scratches, wear, etc.
Connecting rod for failure or piston pin bushing
wear. Measure the bushing for proper clearance.
Refer to " Measuring Piston Pin to Piston Pin Bush­
ing Clearance."
Piston.
PISTON MEASUREMENT
The piston skirts are barrel-shaped so the piston
diameter must be measured at a specific gage point.
m
Clean
• Remove all carbon deposits.
Important
• Do not use a wire brush.
• Remove the carbon from the ring grooves. Use
a ring groove cleaning tool.
Inspect
• Ring land for cracking, wear, etc.
• Ring grooves for burrs, nicks, etc.
• Skirts and pin bosses for cracking.
• Piston dome for cracking.
• Piston skirt for scuffing or deep scratches.
• Oil control ring for wear.
• Connecting rod bearing shells for scoring or
deep pitting.
Measure
• The piston gage point diameter from the top of
the piston to 65.33 mm below to the piston skirt
(figure 36).