Kohler Command PRO CS Service Manual page 116

Section 10
Internal Components
a
b
A
B
C
Figure 10-6. Measuring Cylinder Bore.
If the cylinder bore is badly scored, excessively worn,
tapered, or out of round, resizing is necessary. Use a
measuring device (inside micrometer, etc.) to
determine the amount of wear (refer to the
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.
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.
NOTE: Keep in mind the temperatures caused by
honing may cause inaccurate measurements.
Make sure the bore is cool when measuring.
10.4
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 20° 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 10-7.
Figure 10-7. 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. See Figure 10-6.
Clean Cylinder Bore After Honing
Proper cleaning of the cylinder walls following boring
and/or honing is very critical to a successful overhaul.
Machining grit left in the cylinder bore can destroy an
engine in less than one hour of operation after a
rebuild.
The final cleaning operation should always be a
thorough scrubbing with a brush and hot, soapy water.
Use a strong detergent that is capable of breaking down
the machining oil while maintaining a good level of
suds. If the suds break down during cleaning, discard
the dirty water and start again with more hot water and
detergent. Following the scrubbing, rinse the cylinder
with very hot, clear water. Dry it completely, and apply
a light coating of engine oil to prevent rusting.