Kohler LH630-775 Service Manual page 135

Stem Corrosion: Moisture in fuel or from
condensation are the most common causes of valve
stem corrosion. Condensation occurs from improper
preservation during storage and when engine is
repeatedly stopped before it has a chance to reach
normal operating temperatures. Replace corroded
valves.
Excessive Combustion Temperatures: The white
deposits seen here indicate very high combustion
temperatures, usually due to a lean fuel mixture.
Inspection and Reconditioning
Coking: Coking is normal on intake valves and is not
harmful. If the seat is good, the valve could be reused
after cleaning.
Overheating: An exhaust valve subject to
overheating will have a dark discoloration in the area
above the valve guide. Worn guides and faulty valve
springs may cause this condition. Also check for
clogged air intake, and blocked fins when this
condition is noted.
Section 10
10
10.7