Kohler Command Pro CV980 User Manual Page 100

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Section 9
Inspection and Reconditioning
9.8
Valve Seat Cutter
Pilot
Valve Guides
ȱȱȱȱȱȱ¢ȱęǰȱȱȱ
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 (0.0015/0.0030 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
ȱȱ¢ȱȱȱ¡ȱȱȱ
ȱȱȱęĴȱȱȱ¢ȱǯȱȱ
inserts are not replaceable but can be reconditioned if
ȱȱ¢ȱĴȱȱǯȱȱȱȱ¢ȱ
warped, the cylinder head should be replaced.
Recondition the valve seat inserts following the
ȱȱȱȱȱȱĴȱȱ
ǯȱȱ¢ȱĴȱȱȱȱȱşȬŝǯȱȱęȱ
ȱȱȱȱȱȱŞşǚȱĴȱȱęȱ
ȱȱȱȱȱȱȱşȬŜǯȱĴȱȱ
ȱŚśǚȱȱȱȱȱęȱȱȱ
9-6, and the proper valve seat angle (44.5°, half of the
ȱŞşǚȱǼǰȱȱȱȱȱŖǯśǚȱǻŗǯŖǚȱȱ
cut) interference angle where the maximum pressure
occurs on the outside diameters of the valve face and
seat.
Figure 9-7. Typical Valve Seat Cutter.
Lapping Valves
Reground or new valves must be lapped in, to provide
ȱęǯȱȱȱȱȱȱȱȱȱ
ȱȱęȱǯȱ¢ȱȱȱȱȱȱ
ȱȃęȄȱȱȱȱǰȱȱȱȱ
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
ǯȱĞȱ¢ȱȱ¢ȱǰȱ¢ȱȱ
light coating of SAE 10 oil to prevent rusting.
Valve Stem Seals
These engines use valve stem seals on the intake and
exhaust valves. Always use new seals 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
Ĝȱȱȱȱȱȱ¢ȱȱ
occurs when internal engine temperatures approach
the welding point of the piston. Temperatures high
enough to do this are created by friction, which is
¢ȱĴȱȱȱȱȦȱ
overheating of the engine.
¢ǰȱ¢ȱĴȱȱȱȱȱȱȱ
boss-piston pin area. If the original piston and
ȱȱȱȱȱĞȱȱȱȱ
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.
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