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Leakage: A poor grind on face or seat of valve will
allow leakage resulting in a burned valve on one
side only.
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 over-
heating 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, blocked fins, and lean fuel
mixture when this condition is noted.
Carbon Cut: Excessive build up of deposits in the
combustion chamber may result in valve damage
because deposits can become hard enough to cut
the valve. Cleaning of the cylinder head at proper
intervals could prevent such damage.
Stem Corrosion: Moisture from the 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.
Gum: Gum deposits usually result from using stale
gasoline. This condition is often noted in applica-
tions where fuel is not drained out of the tank dur-
ing the off season. Gum is a prevalent cause of
valve sticking. The cure is to ream the valve
guides and clean or replace the valves, depending
on their condition.
11.5
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