GMC 1976 ZEO 6083 Maintenance Manual page 694

d. Measure and record as "D" the diameter
at the bottom of the cylinder bore and crosswise of
the block.
e. Reading "A" compared to reading "B" and
reading "C" compared to reading "D" indicates cyl-
inder taper.
f. If cylinder taper exceeds 0.005", rebore and
hone to accommodate the next oversize piston,
Reading "A" compared to reading "C" and reading
"B" compared to reading "D" indicates whether or
not the cylinder is out of round. If the out of round
exceeds 0.002", the cylinders must be rebored and
honed for the next oversize piston . A reboring ma-
chine is used when going to oversize pistons. The
following repair data covers honing to oversize by
use of a hone .
REPAIR:
1 . A hone can be used to refinish a cylinder .
2 . Anchor the block solidly for either vertical or
horizontal honing . Use either a drill press or heavy-
duty drill which operates at approximately 250 to
450 rpm .
3 . Connect drill to hone and start drill. Move the
hone up and down in the cylinder approximately 40
cycles per minute . Usually the bottom of the cylinder
must be worked out first because it is smaller. Then
when the cylinder takes a uniform diameter, move
the hone up and down all the way through the bore .
Follow the hone manufacturer's recommendations
for wet or dry honing and oiling the hone.
4. Check the diameter of the cylinder regularly
during honing . A dial bore gauge is the easiest
method but a telescoping gauge can be used . Check
the size at six places in the bore : measure twice at the
top, middle and bottom at 90° angles .
5 . The cross hatch formed by the scratching of
the stones should form an angle of 23° as shown in
Figure 19 . This can be achieved by moving the hone
up and down in the cylinder about 40 cycles per
minute .
6. Clean the cylinder block thoroughly with soap,
water and clean rags . A clean white rag should not
be soiled on the wall after cleaning is complete . Do
not use a solvent or gasoline since they wash the oil
from the walls but leave the metal particles.
7 . Dry the crankcase and coat it with oil.
CRANKSHAFT
Inspect the bearing journals . If they are scored
and cannot be smoothed out by dressing down, re-
place the crankshaft .
BEARINGS
Removal
Installation
ONAN MOTOR GENERATOR 24C- 1 7
AVOID THIS FINISH
PRODUCE CROSS HATCH SCRATCHES
FOR FAST RING SEATING
A-1608
Figure 19-Crosshatching Cylinder
Block
Whenever making major repairs on the engine,
always inspect the drilled passages of the crankshaft .
Clean them to remove any foreign material and to
assure proper lubrication of the connecting rods .
Removing camshaft or crankshaft bearings re-
quires complete disassembly of the engine . Use a
press or a suitable drive plug to remove the bearings .
Support the casting to avoid distortion and avoid
damaging the bearing bore during removal and in-
stallation . Use oil on the bearings to reduce friction
when installing and again lubricate with oil after
installing .
Crankshaft main bearings are precision type
which do not require line reaming or line boring after
installation . They are available in standard size and
.002" undersize. Expand the bearing bore by placing
the casting in hot water or in an oven heated to
200°F. If
a torch is used, apply only a slight amount
of heat.
To ease assembly, cool the precision bearing to
shrink it. Align the oil hole(s) in the bearing with the
oil hole(s) in the bearing bore Figure 20 . The oil
passage must be at least 1/2 open . Lubricate bearings
with SAE20 oil before installing . The cold oiled
precision bearing should require only light taps to
position it with a driving tool. If head of lock pin is
damaged, use side cutters or Easy Out tool to remove
and install new pin. Apply oil to thrust washer (one
used with each bearing) to hold it in place while