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TM 55-1905-220-14-4
3-33.2. EXHAUST VALVE - MAINTENANCE INSTRUCTIONS (Cont).
(3)
Lubricating oil and oil filters should be changed periodcally to avoid the accumulation of sludge.
i
Use only good quality oil as specified for the engine.
(4)
Unsuitable fuels may also cause formation of deposits on the valves, especially when operating at
low temperatures.
(5)
When carbon deposits, due to partially burned fuel, build up around the valve stems and extend to
that portion of the stem which operates in the valve guide, sticking valves will result. The valves cannot seat
properly, and pitted and burned valves and valve seats and loss of compression will result.
(6)
Valve sticking may also result from valve stems which have been scored due to foreign matter in
the lubricating oil, leakage of anti-freeze (glycol) into the lubricating oil which forms a soft, sticky carbon and
gums the valve stems, and bent or worn valve guides. Sticking valves may eventually result in valves being
held in the open position, being struck by the piston, or becoming bent or broken.
(7)
It is highly important that injector timing and valve clearance be accurately adjusted and inspected
periodically. Improperly timed injectors will have adverse effects upon combustion. Tightly adjusted valves will
cause rapid pitting of the valve seats and a hotter running condition on the valve stems.
(8)
The cylinder head must first be removed before the exhaust valves, valve seat inserts, or valve
guides can be removed for replacement or reconditioning.  However, the valve springs may be removed
without removing the cylinder head, if necessary.
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