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10.3
Section 10
Inspection and Reconditioning
10
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.
NOTE: Kohler pistons are custom-machined to
exacting tolerances. When oversizing a
cylinder, it should be machined exactly
0.25 mm (0.010 in.) or 0.50 mm (0.020 in.)
over the new diameter (Section 1). The
corresponding oversize Kohler replacement
piston will then fit correctly.
3. When the bore is within 0.064 mm (0.0025 in.) of
the desired size, remove the coarse stones and
replace them with burnishing stones. Continue
with the burnishing stones until the bore is
within 0.013 mm (0.0005 in.) of the desired size
and then use finish stones (220-280 grit) and
polish the bore to its 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, and
too steep an angle will result in high oil
consumption. See Figure 10-3.
Crankcase
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 blocked cooling fins 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 the amount of wear
(refer to “Specifications, Tolerances, and Special
Torque Values” in Section 1), then select the nearest
suitable oversize of either 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. First, resize using a boring bar, then
use the following procedures for honing the cylinder.
NOTE: Some CV25 engines feature POWER-BORE™
cylinders, a special, patented nickel-silicone
plating process for increased power, superior
oil control, reduced exhaust emission, and
virtually permanent cylinder life. POWER-
BORE™ cylinders cannot be resized or honed
as described in the following procedure. If a
plated cylinder bore is damaged or out of
specification, use a new miniblock or short
block to repair the engine. Use the following
procedures for crankcases with a cast iron
sleeve.
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:
Figure 10-3. Cylinder Bore Crosshatch After
Honing.