GMC 1989 Light Duty Truck, Руководство по ремонту, Страница: 338 / 998

6A-4 GENERAL ENGINE MECHANICAL
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
RECONDITIONING (2.8 L 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 at 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 b efo re re m o vin g from the cylin d e r, and
m easure across the gage co n ta ct points with
outside micrometer, with the gage at the same zero
setting when removed from the cylinder (figure 3).
3. If wear at the top of the cylinder does not exceed
0.10 mm (0 .0 0 4 -in c h ) o u t-o f-ro u n d , h o n in g is
reco m m en d ed for tru in g the bore. If w ear or
out-of-round exceeds these limits, the bore should
be trued up with a boring bar of the fly cutter type,
then finish honed.
If relatively few bores require correction, it will not
be necessary to rebore all cylinders to the same
oversize in order to maintain engine balance. 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 “ H oning.” Make sure the
honing stones are clean, sharp and straight. Move
the hone slowly up and down to produce a 20 to 32
d e g re e c ro s s -h a tc h p a tte rn . C lea n th e bore
thoroughly with soap and water. Dry and rub in
clean engine oil, then re-measure.
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
RECONDITIONING (ALL EXCEPT
2.5 L AND 2.8 L 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 at 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 b efo re rem oving from th e c ylin d e r, and
m easure across the gage co n ta c t points with
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
necessary. 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 to a high limit
piston. 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 sm allest oversize that will perm it com plete
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 re-measure.
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,
m easure all new pistons w ith the m icro m e ter
contacting at points exactly 90 degrees from the
p iston pin c e n te rlin e . Som e p is to n s m ust be
measured at a. specified distance from the piston
crown. Refer to the proper section for additional
instructions. Then select the sm allest piston for the
firs t fittin g . The s lig h t va riatio n u su a lly found
between pistons in a set may provide for correction
in case the first piston is fitted too free.
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