Cylinder Bores, Pistons, Rings, And Connecting Rods; M Easu Ring C Y Lin D E R Bore T A P E R And O U T-O F-R O U N D (All M O D E Ls ); Cylinder Bore Reconditioning (2.5 L Engines) - Chevrolet 1988 Light Duty Truck Repair Manual

CYLINDER BORES, PISTONS, RINGS, AND
MEASURING CYLINDER BORE
TAPER AND OUT-OF-ROUND
(ALL MODELS)
Tool Required:
J 8087 C ylinder Bore Gage
(or equivalent)
• If one or more cylinder bores are rough, scored or
worn beyond limits, it will be necessary to smooth or
true up such bores to fit new pistons.
• No attem pt should be made to cut down oversize
pistons to fit cylinder bores as this will destroy the
s u rfa ce tre a tm e n t and a ffe ct the w e ig h t. The
sm allest possible oversize service pistons should be
used and the cylinder bores should be honed to size
for proper clearances.
1. Refer to " Specifications" in the proper section for
tolerances.
2. Set the gage so that the thrust pin must be forced in
ab o u t 7 mm (1/4-inch) to enter the gage in the
cylinder bore.
3. Center the gage in the cylinder and turn the dial to
" 0 . "
4. Carefully work the gage up and down the cylinder to
determ ine taper and turn it to different points around
the cylin d e r wall to determ ine the out-of-round
condition (figure 1). Measure the bore both parallel
to and at right angles to the engine centerline.
Measure at the top, m iddle and bottom of the bore
and note the readings.
5. R econdition the cylin d e r bore as necessary, as
outlined later.
CYLINDER BORE
RECONDITIONING (2.5 L ENGINES)
1. Measure the cylinder bore for out of round and taper
as outlined previously.
2. Refer to figure 2. Measure dim ension " A" at 13 mm
2
(1 / -inch) below the head gasket surface. Measure
dim ension " B " at 100 mm (4-inches) below the head
gasket surface.
C ylinder bores can be measured by setting the
cylinder gage dial at zero in the cylinder at the point
of desired m easurement. Lock the dial indicator at
ze ro b e fo re re m o v in g from th e c y lin d e r, and
m e asure across the gage c o n ta c t p oints w ith
outside micrometer, with the gage at the same zero
setting when removed from the cylinder (figure 3).
3. If dim ension " A" is larger than dim ension " B " by
0.13 mm (0.005-inch), the cylinder should be bored
for oversized piston and rings.
If relatively few bores require correction, it will not
be necessary to rebore all cylinders to the same
oversize in order to m aintain engine balance. All
oversize service pistons are held to the sam e
weights as standard size pistons.
GENERAL ENGINE MECHANICAL 6A-3
CONNECTING RODS
4. Fine vertical scratches made by ring ends will not,
5. If the bore is glazed but otherwise serviceable,
by them selves, cause excessive oil consum ption;
therefore, honing to remove them is unnecessary.
break the glaze lightly with a hone and replace the
piston rings. Refer to " H oning." Make sure the
honing stones are clean, sharp and straight. Move
the hone slowly up and down to produce a 45
d e g re e c ro s s -h a tc h p a tte rn . C le a n th e
thoroughly with soap and water. Dry and rub in
clean engine oil, then remeasure.
Figure 2— Typical W ear Pattern
bore