Kohler Command CV730 User Manual download pdf (Page 181)

10.8

Section 10

Inspection and Reconditioning

Valve Guides

If a valve guide is worn beyond specifications, it will

not guide the valve in a straight line. This may result

in burnt valve faces or seats, loss of compression, and

excessive oil consumption.

To check valve guide-to-valve stem clearance,

thoroughly clean the valve guide and, using a split-

ball gauge, measure the inside diameter of the guide.

Then, using an outside micrometer, measure the

diameter of the valve stem at several points on the

stem where it moves in the valve guide. Use the

largest stem diameter to calculate the clearance by

subtracting the stem diameter from the guide

diameter. If the intake clearance exceeds

0.038/0.076 mm (0.0015/0.0030p in.) or the exhaust

clearance exceeds 0.050/0.088 mm (0.0020/0.0035 in.),

determine whether the valve stem or guide is

responsible for the excessive clearance.

The maximum (I.D.) wear on the intake valve guide is

7.134 mm (0.2809 in.) while 7.159 mm (0.2819 in.) is

the maximum allowed on the exhaust guide. The

guides are not removable but can be reamed 0.25 mm

(0.010 in.) oversize. Valves with 0.25 mm oversize

stems must then be used.

If the guides are within limits but the valve stems are

worn beyond limits, install new valves.

Valve Seat Inserts

Hardened steel alloy intake and exhaust valve seat

inserts are press-fitted into the cylinder head. The

inserts are not replaceable but can be reconditioned if

not too badly pitted or distorted. If cracked or badly

warped, the cylinder head should be replaced.

Recondition the valve seat inserts following the

instructions provided with the valve seat cutter being

used. A typical cutter is shown in Figure 10-7. The

final cut should be made with an 89° cutter as

specified for the valve seat angle in Figure 10-6.

Cutting the proper 45° valve face angle, as specified in

Figure 10-6, and the proper valve seat angle (44.5°,

half of the full 89° angle), will achieve the desired 0.5°

(1.0° full cut) interference angle where the maximum

pressure occurs on the outside diameters of the valve

face and seat.

Figure 10-7. Typical Valve Seat Cutter.

Lapping Valves

Reground or new valves must be lapped in, to provide

proper fit. Use a hand valve grinder with a suction

cup for final lapping. Lightly coat the valve face with a

“fine” grade of grinding compound, then rotate the

valve on its seat with the grinder. Continue grinding

until a smooth surface is obtained on the seat and on

the valve face. Thoroughly clean the cylinder head in

soap and hot water to remove all traces of grinding

compound. After drying the cylinder head, apply a

light coating of SAE 10 oil to prevent rusting.

Intake Valve Stem Seal

These engines use valve stem seals on the intake

valves. Always use a new seal when the valves are

removed from the cylinder head. The seals should also

be replaced if deteriorated or damaged in any way.

Never reuse an old seal.

Pistons and Rings

Inspection

Scuffing and scoring of pistons and cylinder walls

occurs when internal engine temperatures approach

the welding point of the piston. Temperatures high

enough to do this are created by friction, which is

usually attributed to improper lubrication and/or

overheating of the engine.

Normally, very little wear takes place in the piston

boss-piston pin area. If the original piston and

connecting rod can be reused after new rings are

installed, the original pin can also be reused but new

piston pin retainers are required. The piston pin is

included as part of the piston assembly – if the pin

boss in the piston or the pin are worn or damaged, a

new piston assembly is required.

Valve Seat

Cutter

Pilot

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Kohler Command CV730 User Manual Page 181

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