Kohler Command PRO EFI propane PCH680 [71/96] Disassembly inspection and service

Valve Guides

If a valve guide is worn beyond speciﬁ cations, it will not guide 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 valve guide and, using a split-ball gauge, measure

inside diameter of guide. Then, using an outside micrometer, measure diameter of valve stem at several points on

stem where it moves in valve guide. Use largest stem diameter to calculate clearance by subtracting stem diameter

from guide diameter. If intake clearance exceeds 0.038/0.076 mm (0.0015/0.0030 in.) or exhaust clearance exceeds

0.050/0.088 mm (0.0020/0.0035 in.), determine whether valve stem or guide is responsible for excessive clearance.

Maximum (I.D.) wear on intake valve guide is 7.134 mm (0.2809 in.) while 7.159 mm (0.2819 in.) is maximum allowed

on exhaust guide. 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 guides are within limits but valve stems are worn beyond limits, install new valves.

Valve Seat Inserts

Hardened steel alloy intake and exhaust valve seat inserts are press ﬁ tted into cylinder head. Inserts are not

replaceable but can be reconditioned if not too badly pitted or distorted. If cracked or badly warped, cylinder head

should be replaced.

Recondition valve seat inserts following instructions provided with valve seat cutter being used. Final cut should

be made with an 89° cutter as speciﬁ ed for valve seat angle. Cutting proper 45° valve face angle as speciﬁ ed, and

proper valve seat angle (44.5°, half of full 89° angle), will achieve desired 0.5° (1.0° full cut) interference angle where

maximum pressure occurs on outside diameters of valve face and seat.

Lapping Valves

NOTE: Exhaust valves that are black in color cannot be ground and do not require lapping.

Reground or new valves must be lapped in, to provide proper ﬁ t. Use a hand valve grinder with a suction cup for ﬁ nal

lapping. Lightly coat valve face with a ﬁ ne grade of grinding compound, then rotate valve on its seat with grinder.

Continue grinding until a smooth surface is obtained on seat and on valve face. Thoroughly clean cylinder head in

soap and hot water to remove all traces of grinding compound. After drying cylinder head, apply a light coating of SAE

10 oil to prevent rusting.

Valve Stem Seal

These engines use valve stem seals on intake and exhaust valves. Always use a new seal when valves are removed

from cylinder head. Seals should also be replaced if deteriorated or damaged in any way. Never reuse an old seal.

Disassembly/Inspection and Service

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