GMC 1989 Light Duty Truck, Repair Manual, Page: 342 / 998

6A-8 GENERAL ENGINE MECHANICAL
• R efer to “ S p e c ific a tio n s ” in th e p ro p e r
section. Determine if the piston clearance is in
the acceptable range.
2. If the used piston is not acceptable, determine if a
new piston can fit the cylinder bore.
3. If a new piston does not bring the clearance within
tolerances, the cylinder bore must be reconditioned.
4. Mark the piston to identify the cylinder for which it
was fitted.
ASSEMBLY
Assembling the Piston and Connecting Rod
All except 6.2 L Engines)
*
A ssem ble (Figure 13)
excessive with a new piston pin, the connecting rod
must be replaced. Replacement bushings are not
available.
PISTON SELECTION
(2.5 L AND 2.8 L ENGINES)
Refer to the proper section.
PISTON SELECTION
(ALL EXCEPT 2.5 L
AND 2.8 L ENGINES)
1. Check the used piston to cylinder bore clearance.
M easure (Figures 11 and 12)
$
C ylinder bore diameter. Use a telescoping
bore gage, located 65 mm (2 1/
2
-inches) below
the top of the cylinder bore (figure 11).
Piston diameter. Measure the piston skirt at a
right angle to the piston pin, at the centerline
of the piston pin (figure 12).
Subtract the piston diameter from the cylinder
bore diam eter to determ ine piston to bore
clearance.
Tool Required:
J 24086 Piston Pin Remover
and Installer Set
1. Piston and connecting rod.
• The piston and co n n e c tin g rod m ust be
installed in the proper position.
— 2.5 L Engines: The raised notch side of
the connecting rod must be opposite the
notch in the piston crown.
— 2.8 L E n g in e s : T h e b e v e l on th e
connecting rod should face the outside
of the engine.
— 4.8 L Engines: The flat side of the piston
crown depression and the connecting
rod bearing tang slot must be on the
same side.
— All Others: The valve cutouts in the
p iston crow n m ust be o p p o s ite the
connecting rod bearing tangs.
• Lubricate the piston pin holes in the piston
and connecting rod with engine oil.
• Install the pin guide (item E, figure 13) to hold
the piston and connecting rod together. Be
sure to use the proper pin guide. Refer to the
instructions supplied with the tool.
2. Piston pin.
• Insert the piston pin into the piston pin hole.
• Place the assembly on the support fixture
(figure 13).
• Adjust the piston pin installer (J 24086-9) to
the correct length, using the letter-number
scale on the installer adjuster (figure 13). This
is necessary to insure that the piston pin is
pressed into the piston to the correct depth.
Refer to the instructions supplied with the tool
for the proper setting.
• Lock the adjuster in place with the lock ring.
NOTICE: A fte r the in staller hub b o tto m s on the
s u pp o rt assem bly, do n o t e x c e e d 35 0 0 0 kPa
(5 ,0 0 0 p s i) p re s s u re , as th is c o u ld c a u s e
dam age to the tool.
B-09447
Fsgure 1 2 - -M easuring th e Piston Skirt
Place the adjuster in the support fixture. Press
the piston pin into place (until the adjustable
installer bottoms in the support fixture).