Valve Guides; Valve Seat Inserts; Lapping Valves; Pistons And Rings - Kohler Courage SV470-600 Service Manual

Valve Guides

If a valve guide is worn beyond specifications, it will not
guide the valve in a straight line. This may result in
burned 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
6.135 mm (0.2415 in.) while 6.160 mm (0.2425 in.) is
the maximum allowed on the exhaust guide. The
guides are not removable. If the guides are within limits
but the valve stems are worn beyond limits, replace the
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 they can be
reconditioned if not too badly pitted or distorted. If the
seats are 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 9-11. The final
cut should be made with an 89° cutter as specified for
the valve seat angle in Figure 9-10. With the proper
45° valve face angle, 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 valve face and seat.
www.SmallEngineDiscount.com
Valve Seat Cutter
Figure 9-11. Typical Valve Seat Cutter.

Lapping Valves

Reground or new valves must be lapped in, to provide
a good seal. 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 prevent
rusting.

Pistons and Rings

Inspection
Scuffing 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.
Ring failure is usually indicated by excessive oil
consumption and blue exhaust smoke. When rings
fail, oil is allowed to enter the combustion chamber
where it is burned along with the fuel. High oil
consumption can also occur when the piston ring end
gap is incorrect because the ring cannot properly
conform to the cylinder wall under this condition. Oil
control is also lost when ring gaps are not staggered
during installation.
Not For Resale
Inspection and Reconditioning
Pilot
Section 9
9
9.9