GMC T Series 1994 Repair Manual page 304

cylinder, and measure across the gage contact
points with an outside micrometer, with the
gage at the same zero setting when removed
from the cylinder (figure 3).
3. If dimension "A" is larger than dimension " 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 maintain engine bal­
ance. All oversize service pistons are held to
the same weights as standard size pistons.
4. Fine vertical scratches made by ring ends will not,
by themselves, cause excessive oil consumption;
therefore, honing to remove them is unnecessary.
5. If the bore is glazed but otherwise serviceable,
break the glaze lightly with a hone and replace the
piston rings. Refer to " Honing."
• Make sure the honing stones are clean, sharp,
and straight. Move the hone slowly up and
down to produce a 45 degree cross-hatch pat­
tern. Clean the bore thoroughly with soap and
water. Dry and rub in clean engine oil, then
remeasure.
6. If honing is not required, the cylinder bores should
be cleaned with a hot water and detergent wash.
Apply clean engine oil to the bore after cleaning.
CYLINDER BORE
RECO NDITIO NING (ALL EXCEPT
2.2L ENGINES)
1. Measure the cylinder bore for out-of-round and
taper, as outlined previously.
2. Refer to figure 2. Measure for wear at the top of
the bore (point "A" ) and the bottom (point " B" ).
• Cylinder bores can be measured by setting the
cylinder gage dial at zero in the cylinder at the
point of desired measurement. Lock the dial
indicator at zero before removing it from the
cylinder, and measure across the gage contact
points with an outside micrometer, with the
gage at the same zero setting when removed
from the cylinder (figure 3).
3. If the cylinders are found to exceed the specified
out-of-round or taper, honing or boring will be nec­
essary. Any cylinders that were found to have less
than 0.13 mm (0.005 inch) wear or taper may not
entirely clean up when fitted with a high limit pis­
ton. If it is desired to entirely clean up the bore in
these cases, it will be necessary to rebore for an
oversize piston. If more than 0.13 mm (0.005 inch)
taper or wear, they should be bored and honed to
the smallest oversize that will permit complete
resurfacing of all cylinders.
4. Fine vertical scratches made by ring ends will not,
by themselves, cause excessive oil consumption;
therefore, honing to remove them is unnecessary.
5. If the bore is glazed but otherwise serviceable,
break the glaze lightly with a hone and replace the
piston rings.
• Make sure the honing stones are clean, sharp,
and straight. Move the hone slowly up and
down to produce a 45 to 65 degree cross-hatch
pattern. Clean the bore thoroughly with soap
and water. Dry and rub in clean engine oil, then
remeasure.
6. If honing is not required, the cylinder bores should
be cleaned with a hot water and detergent wash.
Apply clean engine oil to the bore after cleaning.
BORING
1. Before the honing or reboring operation is started,
measure all new pistons with the micrometer con­
tacting at points exactly 90 degrees from the piston
pin centerline. Some pistons must be measured at
a specified distance from the piston crown. Refer to
the proper section for additional instructions. Then
select the smallest piston for the first fitting. The
slight variation usually found between pistons in a
set may provide for correction in case the first pis­
ton is fitted too loose.
2. Before using any type of boring bar, the top of the
cylinder block should be filed to remove any dirt or
burrs. This is very important. If not checked, the
boring bar may be tilted which would result in the
rebored cylinder wall not being at right angles to
the crankshaft.
3. The instructions furnished by the manufacturer of the
equipment being used should be carefully followed.
4. When reboring cylinders, all crankshaft bearing
caps must be in place and tightened to the proper
torque to avoid distortion of bores in the final
assembly. Always make sure the crankshaft is out
of the way of the boring cutter when boring each
cylinder. Crankshaft bearings and other internal
parts must be covered or taped to protect them
during the boring or honing operation.
5. When taking the final cut with a boring bar, leave
0.03 mm (0.001 inch) on the diameter for finish
honing to give the required position to the cylinder
clearance specifications. (The honing or boring
operation must be done carefully so the specified
clearance between pistons, rings, and cylinder
bores is maintained).
J Important