GMC 1982 Light Duty Truck, Service Manual

Page: 724 / 1435

6A5-28 MARK IV
2. Lightly coat pistons, rings and cylinder walls with light
engine oil.
3. With bearing caps removed, install Tool J-5329 (3 /8 ")
on connecting rod bolts.
4. Install each connecting rod and piston assembly in its
respective bore. Install with connecting rod bearing
tang slots on side opposite camshaft. Use Tool J-8037
to compress the rings. Guide the connecting rod into
place on the crankshaft journal with Tool J-6305 (11/
32"). Use a hammer handle and light blows to install
the piston into the bore. Hold the ring compressor
firmly against the cylinder block until all piston rings
have entered the cylinder bore.
5. Remove Tool J-5329.
6. Install the bearing caps and torque nuts to
specifications.
Be sure to install new pistons in the cylinders for which
they were fitted, and used pistons in the cylinder from which
they were removed. Each connecting rod and bearing cap
should be marked, beginning at the front of the engine.
Cylinders 1,3,5 and 7 in the left bank and, 2 4, 6 and 8 in 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 one block
or cylinder to another, new bearings should be fitted and the
connecting rod should be numbered to correspond with the
new cylinder number.
CYLIN D ER BLOCK
C le a n in g a n d Inspection
1. Wash cylinder block thoroughly in cleaning solvent and
clean all gasket surfaces.
2. Remove oil gallery plugs and clean all oil passages.
3. Clean and inspect water passages in the cylinder block.
4. Inspect the cylinder block for cracks in the cylinder
walls, water jacket, valve lifter bores and main bearing
webs.
5. Measure the cylinder walls for taper, out-of-round or
excessive ridge at top of ring travel. This should be done
with a dial indicator. Set the gage so that the thrust pin
must be forced in about 1/4" (6.5m m ) to enter gage in
cylinder bore. Center gage in cylinder and turn dial to
"0". Carefully work gage up and down cylinder to
determine taper and turn it to different points around
cylinder wall to determine the out-of-round condition.
If cylinders were found to exceed specifications, honing
or boring will be necessary.
C o n d itio n in g
The performance of the following operation is contin­
gent upon engine condition at time of repair.
If the cylinder block inspection indicated that the block
was suitable for continued use except for out-of-round or
tapered cylinders, they can be conditioned by honing or
boring.
If the cylinders were found to have less than .005"
taper or wear, they can be conditioned with a hone and fitted
with the high limit standard size piston. A cylinder bore of
less then .005 " 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 .005" taper or wear, they
should be bored and honed to the smallest oversize that will
permit complete resurfacing of all cylinders.
When pistons are being fitted and honing is not
necessary, cylinder bores may be cleaned with a hot water
and detergent wash. A fter cleaning, the cylinder bores
should be swabbed several times with light engine oil and a
clean cloth and then wiped with a clean dry cloth.
B oring
1. Before using any type boring bar, the top of the
cylinder block should be filed off 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.
2. The piston to be fitted should be measured with a
micrometer, measuring at the center of the piston skirt
and at right angles to the piston pin. The cylinder
should be bored to the same diameter as the piston and
honed to give the specified clearance.
3. The instructions furnished by the manufacturer of the
equipment being used should be carefully followed.
H o n in g
1. When cylinders are to be honed, follow the hone
manufacturer’s recommendations for the use of the
hone and cleaning and lubrication during honing.
2. Occasionally during the honing operation, the cylinder
bore should be thoroughly cleaned and the piston
selected for the individual cylinder checked for correct
fit.
3. When finish honing a cylinder bore to fit a piston, the
hone should be moved up and down at a sufficient speed
to obtain very fine uniform surface finish marks, in a
cross-hatch pattern of approximately 45° to 65° in­
cluded angle. The finish marks should be clean but not
sharp, free from imbedded particles and torn or folded
metal.
4. Permanently mark the piston for the cylinder to which
it has been fitted and proceed to hone cylinders and fit
the remaining pistons.
N O T IC E : H andle the pistons with care and do not
attempt to force them through the cylinder until the
cylinder has been honed to correct size as this type
piston can be distorted through careless handling.
5. Thoroughly clean the bores with hot water and deter­
gent. Scrub well with a stiff bristle brush and rinse
thoroughly with hot water. It is extremely essential that
a good cleaning operation be performed. If any of the
abrasive material is allowed to remain in the cylinder
bores, it will rapidly w err the new rings and cylinder
bores in addition to the bearings lubricated by the
contaminated oil, the bores should be swabbed and then
wiped with a clean dry cloth. Cylinder should not be
cleaned with kerosene or gasoline. Clean the remainder
of the cylinder block to remove the excess material
spread during the honing operation.
Piston S election
1. Check U S E D piston to cylinder bore clearance as
follows: