Kohler COMMAND CV11-16 Service Manual page 120

Section 10
Inspection and Reconditioning
Valve Guides
If a valve guide is worn beyond specifi cations, 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 with Tool No. KO1026.
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 fi tted 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 10-6. The fi nal
cut should be made with an 89° cutter as specifi ed for
the valve seat angle in Figure 10-5. With the proper
45° valve face angle as specifi ed in Figure 10-4
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 10-6. Typical Valve Seat Cutter.
Lapping Valves
Reground or new valves must be lapped in, to provide
fi t. Use a hand valve grinder with suction cup for fi nal
lapping. Lightly coat valve face with ''fi ne'' 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 SAE 10 oil to prevent
rusting.
Valve Stem Seals
These engines use valve stem seals on the intake
valves and sometimes on the exhaust. 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.
Pistons and Rings
Inspection
Scuffi ng and scoring of pistons and cylinder walls
occurs when internal 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 part
of the piston assembly; if the pin boss or the pin are
worn or damaged, a new piston assembly is required.