Section 9
Inspection and Reconditioning
9
9.3
1. Lower hone into bore and after centering, adjust
so 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 9-3.
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
11 mm (0.433 in.)
above the bottom of
the piston skirt and perpendicular to the piston
pin. See Figure 9-4.
Figure 9-3. 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.
Figure 9-4. Measuring Piston Diameter.
11 mm (0.433 in.)
Measure 11 mm above the
Bottom of Piston Skirt at
Right Angles to Piston Pin
