TM 5-3810-300-24&P-3
1.2.2
EXHAUST VALVES
Four exhaust valves are provided for each cylinder (Fig.
2). 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.
Pre-finished replaceable valve guides are pressed into
the cylinder head (Fig. 3). Reaming of these guides is
unnecessary.
Certain engines are equipped with
exhaust valve guide oil seals.
Exhaust valve seat inserts are pressed into the cylinder
head and permit accurate seating of the exhaust valves
under varying conditions of temperature and materially
Fig. 2 - Location of Exhaust Valves
prolong the life of the cylinder head (Fig. 3). The inserts
are ground to very close limits and the freedom from
for proper operation of the engine. Too little clearance
warpage, under ordinary conditions, reduces valve
between the exhaust valve stem and the rocker arm
reconditioning to a minimum. The exhaust valves and
causes a loss of compression, misfiring cylinder, and
valve seat inserts are ground to an approximate 30"
eventual burning of the valves and valve seat inserts.
seating angle.
Too much clearance results in noisy operation of the
engine, especially in the idling speed range. Refer to
The exhaust valve springs are held in place by the valve
spring caps and tapered two-piece valve locks (Fig. 3).
adjusting the valve clearance.
Exhaust Valve Maintenance
Excess oil from the rocker arms lubricates the exhaust
valve stems. The valves are cooled by the flow of air
Efficient combustion in the engine requires that the
from the blower past the valves each time the air inlet
exhaust valves be maintained in good operating
ports are uncovered.
condition. Valve seats must be true and unpitted to
assure leakproof seating, valve stems must work freely
Exhaust Valve Clearance
and smoothly within the valve guides, and the correct
Correct valve clearance adjustment is important
valve clearance must be provided.
Proper maintenance and operation of the engine is
important to long valve life.
Engine operating
temperature should be maintained between 160F. And
1850F. 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.
Lubricating oil and oil filters should be changed
periodically to avoid the accumulation of sludge. Use only
good quality oil as specified for the engine.
Unsuitable fuels may also cause formation of deposits on
the valves, especially when operating at low
temperatures.
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