Kohler LH630-775 Service Manual page 131

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.
Inspection and Reconditioning
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.
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.
Measuring Piston-to-Bore Clearance
Before installing the piston into the cylinder bore, it is
necessary that the clearance be accurately checked.
This step is often overlooked, and if the clearances are
not within specifications, engine failure will usually
result.
NOTE: Do not use a feeler gauge to measure piston-
to-bore clearance–it will yield inaccurate
measurements. Always use a micrometer.
Use the following procedure to accurately measure
the piston-to-bore clearance:
1. Use a micrometer and measure the diameter of
the piston 6 mm (0.24 in.) above the bottom of
the piston skirt and perpendicular to the piston
pin. See Figure 10-4.
Section 10
10
10.3