Kohler COMMAND CV17-745 Service Manual page 159

Kohler Engine Parts Call K&T 606-678-9623 or 606-561-4983
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. Initially, 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:
1. Lower hone into bore and after centering, adjust so
2. With the lower edge of each stone positioned even
NOTE: Kohler pistons are custom-machined to
3. When the bore is within 0.064 mm (0.0025 in.) of
Figure 10-3. Cylinder Bore Crosshatch after
Honing.
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Inspection and Reconditioning
that the stones are in contact with the cylinder
wall. Use of a commercial cutting-cooling agent is
recommended.
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.
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.
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.
Section 10
10
10.3