3-33.2. EXHAUST VALVE - MAINTENANCE INSTRUCTIONS (Cont).
Refer to step 3.
Refer to step 4.
Carbon on the face of a valve indi-
cates blow-by due to a faulty seat.
Black carbon deposits extending from
the valve guides may result from
cold operation due to light loads or
the use of too light a grade of fuel.
Rusty brown valve heads with carbon
deposits forming narrow collars near
the valve guides evidence hot opera-
tion due to overloads, inadequate
cooling, or improper timing which
results in carbonization of the
Clean the carbon from the valve
stems and wash the valves with fuel
oil. The valve stems must be free
from scratches or scruff marks and
the valve faces must be free from
ridges, cracks, or pitting. If
necessary, reface the valves or
install new valves. If the valve
heads are warped, replace the
If there is evidence of engine oil
running down the exhaust valve stem
into the exhaust chamber, creating a
high oil consumption condition
because of excessive idling and
resultant low engine exhaust back
pressures, install valve guide oil