Kohler Command CV730 User Manual download pdf (Page 176)

10.3

Section 10

Inspection and Reconditioning

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.

1 2 ... 171 172 173 174 175 176 177 178 179 180 181 ... 216 217

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Kohler Command CV730 User Manual Page 176

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