DETROIT DIESEL 53
1.2.2
EXHAUST VALVES
Four exhaust valves are provided for each cylinder,
Proper maintenance and operation of the engine is
(Fig. 1). The valve heads are heat treated and ground
important to long valve life.
Engine operating
to the proper seat angle and diameter. The valve stems
temperatures should be maintained between 160F.
are ground to size and hardened at the end which
and 185F. Low operating temperatures (usually due to
contacts the rocker arm or the exhaust valve bridge.
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.
valve guides which are pressed into the cylinder head.
and a greater tendency for lubricating oil to sludge.
Exhaust valve seat inserts, pressed into the cylinder
head, permit accurate seating of the exhaust valves
Unsuitable fuels may also cause formation of deposits
under varying conditions of temperature and materially
on the valves, especially when operating at low
prolong the life of the cylinder head. The exhaust
temperatures.
valves and exhaust valve seat inserts are ground to a
30 seating angle.
When carbon deposits, due to partially burned fuel, build
up around the valve stems and extend to that portion of
The exhaust valve springs are held in place by the valve
the stem which operates in the valve guide, sticking
spring caps and tapered two-piece valve locks.
valves will result. Thus, the valves cannot seat properly
and pitted and burned valves and valve seats and loss
of compression will result.
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
Lubricating oil and oil filters should be changed
ports are uncovered.
periodically to avoid accumulation of sludge.
Valve sticking may also result from valve stems which
Exhaust Valve Maintenance
have been scored due to foreign matter in the
lubricating oil, leakage of antifreeze (glycol) into the
Efficient combustion in the engine requires that the
lubricating oil which forms a soft sticky carbon and gums
exhaust valves be maintained in good operating
the valve stems, and bent or worn valve guides.
condition. Valve seats must be true and unpitted to
Sticking valves may eventually result in valves being
assure leak-proof seating, valve stems must work freely
held in the open position, being struck by the piston and
and smoothly within the valve guides and the correct
becoming bent or broken.
valve clearance (Section 14.1) must be maintained.
It is highly important that injector timing and valve
clearance be accurately adjusted and checked periodi-
cally. 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
1972 General Motors Corp.
February, 1972
SEC 1.2.2 Page 1
