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 TM 55-1905-220-14-6
3-165.2. EXHAUST VALVE - MAINTENANCE INSTRUCTIONS.
a. General.
(1) Four exhaust valves are provided for each cylinder. The valve heads are heat-treated and ground to
the proper seat angle and diameter, and the valve stems are ground to size and hardened at the end
which contacts the rocker arm or exhaust valve bridge.
(2) Pre-finished, replaceable valve guides, are pressed into the cylinder head. Reaming of these guides
is unnecessary.
(3) Exhaust valve seat inserts pressed into the cylinder head permit accurate seating of the exhaust
valves under varying conditions of temperature and materially prolongs the life of the cylinder head.
The inserts are ground to very close limits and the freedom from warp-age, under ordinary
conditions, reduces valve reconditioning to a minimum. The exhaust valves and valve seat inserts
are ground to a 300 angle.
(4) The exhaust valve springs are held in place by the valve spring caps and tapered two-piece valve
locks.
(5) Excess oil from the rocker arms lubricates the exhaust valve stems.. The valves are cooled by the
flow of air from the blower past the valves each time the air inlet ports are uncovered.
b. Exhaust Valve Clearance Adjustment.
Correct valve clearance adjustment is important for proper operation of the engine. Too little clearance
between the exhaust valve stem and the rocker arm causes loss of compression, misfiring cylinders, and
eventual burning of the valves and valve seat inserts. Too much clearance results in noisy operation of the
engine, especially in the idling speed range.
c. Exhaust Valve Maintenance.
(1) Efficient combustion in the engine requires that the exhaust valves be maintained in good operating
condition. Valve seats must be true and unpitted to assure leakproof seating. Valve stems must
work freely and smoothly within the valve guides and the correct valve clearances must be provided.
(2) Proper maintenance and operation of the engine is important to long valve life. Engine operating
temperature should be maintained between 1600 F and 1850 F (710C to 850C). Low operating
temperatures, usually due to extended periods of idling or light engine loads, result in incomplete
combustion, formation of excessive carbon deposits and fuel lacquers on valves and related parts,
and a greater tendency for lubricating oil to sludge.
3-2759
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