DETROIT DIESEL 53
1.2.2
EXHAUST VALVES
Four exhaust valves are provided for each cylinder (Fig. I). The valve heads are heat treated and ground to the proper
seat angle and diameter. The valve stems are ground to size and hardened at the end which contacts the rocker arm or
the exhaust valve bridge.
The exhaust valve stems are contained within exhaust valve guides which are pressed into the cylinder head. Exhaust
valve seat inserts, pressed into the cylinder head, permit accurate seating of the exhaust valves under varying conditions
of temperature and materially prolong the life of the cylinder head. The exhaust valves and exhaust valve seat inserts
are ground to a 30 e seating angle.
The exhaust valve springs are held In place by the valve spring caps and tapered two-piece valve locks.
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.
Exhaust Valve Maintenance
Efficient combustion in the engine requires that the exhaust valves be maintained in good operating condition. Valves
seats must be true and unpitted to assure leak-proof seating, valve stems must work freely and smoothly within the valve
guides and the correct valve clearance (Section 14.1) must be maintained.
Proper maintenance and operation of the engine is important to long valve life. Engine operating temperatures should be
maintained between 160 F. and 185 F. 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.
Unsuitable fuels may also cause formation of deposits on the valves, especially when operating at low temperatures.
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. Thus, the valves cannot seat properly and pitted and
burned valves and valve seats and loss of compression will result.
Lubricating oil and oil filters should be changed periodically to avoid accumulation of sludge.
Valve sticking may also result from valve stems which have been scored due to foreign matter in the lubricating oil,
leakage of antifreeze (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 and becoming bent or broken.
It is highly important that injector timing and valve clearance be accurately adjusted and checked 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.
Fig. 1 - Location of Exhaust valves
Fig. 2 - Removing Valve Spring
August, 1972
SEC. 1.2.2
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