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10.3
Section 10
Inspection and Reconditioning
10
Crankcase
These engines contain a cast-iron cylinder liner that
may be reconditioned as follows:
Inspection and Service
Check all gasket surfaces to make sure they are free
of gasket fragments. Gasket surfaces must also be
free of deep scratches or nicks.
Check the cylinder bore for scoring. In severe cases,
unburned fuel can cause scuffing and scoring of the
cylinder wall. It washes the necessary lubricating oils
off the piston and cylinder wall. As raw fuel seeps
down the cylinder wall, the piston rings make metal to
metal contact with the wall. Scoring of the cylinder wall
can also be caused by localized hot spots resulting
from a cooling system problem or from inadequate or
contaminated lubrication.
If the cylinder bore is badly scored, excessively worn,
tapered, or out-of-round, resizing is necessary. Use an
inside micrometer to determine amount of wear (refer
to the “Specifications, Tolerances, and Special Torque
Values”, in Section 1), then select the nearest suitable
oversize of either 0.08 mm (0.003 in.), 0.25 mm
(0.010 in.), or 0.50 mm (0.020 in.). Resizing to one of
these oversizes will allow usage of the available
oversize piston and ring assemblies. Initially, resize
using a boring bar, then use the following procedures
for honing the cylinder.
NOTE: If the bore is beyond the wear limit, a new
miniblock or short block will be required.
Honing
While most commercially available cylinder hones can
be used with either portable drills or drill presses, the
use of a low speed drill press is preferred as it
facilitates more accurate alignment of the bore in
relation to the crankshaft crossbore. Honing is best
accomplished at a drill speed of about 250 RPM and
60 strokes per minute. After installing coarse stones in
hone, proceed as follows:
1. Lower hone into bore and after centering, adjust
so that the stones are in contact with the cylinder
wall. Use of a commercial cutting-cooling agent is
recommended.
2. With the lower edge of each stone positioned
even with the lowest edge of the bore, start drill
and honing process. Move the hone up and down
while resizing to prevent the formation of cutting
ridges. Check the size frequently.
3. When the bore is within 0.064 mm (0.0025 in.) of
desired size, remove the coarse stones and
replace with burnishing stones. Continue with the
burnishing stones until within 0.013 mm
(0.0005 in.) of desired size and then use finish
stones (220-280 grit) and polish to final size. A
crosshatch should be observed if honing is done
correctly. The crosshatch should intersect at
approximately 23-33° off the horizontal. Too flat
an angle could cause the rings to skip and wear
excessively, too steep an angle will result in high
oil consumption. See Figure 10-3.
Figure 10-3. Cylinder Bore Crosshatch After Honing.
4. After resizing, check the bore for roundness,
taper, and size. Use an inside micrometer,
telescoping gauge, or bore gauge to take
measurements. The measurements should be
taken at three locations in the cylinder-at the top,
middle, and bottom. Two measurements should
be taken (perpendicular to each other) at each of
the three locations.