Intake And Exhaust Manifolds; Camshaft; Camshaft Bearings; Timing Chain And Sprockets - GMC 1990 Light Truck Repair Manual

m
M e a su re
Piston pin diameter and clearance.
Piston to bore clearance, and fit pistons as outlined.
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A s s e m b le
Components as outlined.
Im p o rta n t
• Each connecting rod and bearing cap should
be marked, beginning at the front of the
engine. Cylinders 1, 3 and 5 are at the left
bank, and 2, 4 and 6 are the right bank. The
numbers on the connecting rod and bearing
cap must be on the same side when installed
in the cylinder bore. If a connecting rod is ever
transposed from block or cylinder to another,
new connecting rod bearings should be fitted
and the connecting rod should be numbered
to correspond with the new cylinder number.
M e a su re
• Ring end gap and ring clearance.
In s p e ct
L *
Ring fit.
INTAKE AND EXHAUST
MANIFOLDS
Old pieces of gasket from the gasket surfaces.
Excessive carbon build-up in the exhaust passages
of the intake manifold.
Scale and deposits from the coolant passages of the
intake manifold.
EGR passage of excessive carbon deposits.
In s p e c t (F ig u re 14)
Manifolds for cracks, broken flanges, and gasket
surface damage.
4.3 LITER V-6 6A3-11
Alignment of manifold flanges. Use a straight edge
and feeler gage. If the flanges do not align, the
manifold is warped and should be replaced.

CAMSHAFT

Im p o rta n t
Whenever the camshaft needs to be replaced, a
new set of lifters must also be installed.
Camshaft lobes and journals for scratches, pitting,
scoring, and wear.
M ea su re
Camshaft journal diameter (figure 15). The proper
diameter is listed in " Specifications."

CAMSHAFT BEARINGS

Refer lo GENERAL ENGINE MECHANICAL (SEC. 6A)
for replacement procedures.

TIMING CHAIN AND SPROCKETS

L*
In sp e ct
• Sprockets for chipped teeth and wear.
• Timing chain for damage.
• It should be noted that excessively worn sprockets
will rapidly wear a new chain. Likewise, an
excessively worn chain will rapidly wear a new set of
sprockets.
CRANKSHAFT SPROCKET REPLACEMENT
R em o ve o r D is c o n n e c t (F ig u re 16)
Tool Required:
J 5825-A Crankshaft Sprocket Puller
1. Crankshaft sprocket using J 5825-A.
2. Key (if necessary).