Kohler LH630-775 Service Manual page 136

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. 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. If the intake
clearance exceeds 0.038/0.076 mm (0.0015/0.003 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.
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, replace with 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 on the engines 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. With
the proper 45° valve face angle as specified in Figure
10-6 and the valve seat cut properly (44.5° as
measured from centerline when cut 89°) this would
result in the desired 0.5° (1.0° full cut) interference
angle where the maximum pressure occurs on the
outside diameters of valve face and seat.
10.8
Valve Seat Cutter
Pilot
Figure 10-7. Typical Valve Seat Cutter.
Lapping Valves
Reground or new valves must be lapped in, to
provide fit. Use a hand valve grinder with suction
cup for final lapping. Lightly coat valve face with
"fine" grade of grinding compound, then rotate valve
on seat with grinder. Continue grinding until 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
engine oil to the seats to prevent rusting.
Intake Valve Stem Seal
These engines use valve stem seals on the intake
valves. Always use a new seal when valves are
removed from cylinder head. The seals should also be
replaced if deteriorated or damaged in any way.
Never reuse an old seal.