DETROIT DIESEL 53
1.2.2
EXHAUST VALVES
Proper maintenance and operation of the engine is
Four exhaust valves are provided for
important to long valve life. Engine operating
each cylinder
temperatures should be maintained between 160 F.
(Fig. 1). The valve heads are heat treated and ground
and 185oF. Low operating temperatures (usually due
to the proper seat angle and diameter. The valve stems
to extended periods of idling or light engine loads)
are ground to size and hardened at the end which
result in incomplete combustion. formation of
contacts the rocker arm or the exhaust valve bridge.
excessive carbon deposits and fuel lacquers on valves
and related parts. and a greater tendency for
The exhaust valve stems are contained within exhaust
lubricating oil to sludge.
valve guides which are pressed into the cylinder head.
Exhaust valve seat inserts, pressed into the cylinder
Unsuitable fuels may also cause formation of deposits
head, permit accurate seating of the exhaust valves
on the valves, especially when operating at low
under varying conditions of temperature and materi-
temperatures.
ally prolong the life of the cylinder head. The exhaust
valves and exhaust valve seat inserts are ground to a
When carbon deposits, due to partially burned fuel,
30o seating angle.
build up around the valve stems and extend to that
portion of the stem which operates in the valve guide,
The exhaust valve springs are held in place by the
sticking valves will result. Thus, the valves cannot seat
valve spring caps and tapered two-piece valve locks.
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
Lubricating oil and oil filters should be changed
from the blower past the valves each time the air inlet
periodically to avoid accumulation of sludge.
ports are uncovered.
Valve sticking may also result from valve stems which
have been scored due to foreign matter in the
Exhaust Valve Maintenance
lubricating oil, leakage of antifreeze (glycol) into the
lubricating oil which forms a soft sticky carbon and
Efficient combustion in the engine requires that the
gums the valve stems. and bent or worn valve guides.
exhaust valves be maintained in good operating
Sticking valves may eventually result in valves being
condition. Valve seats must be true and unpitted to
held in the open position, being struck by the piston
assure leak-proof seating, valve stems must work freely
and becoming bent or broken.
and smoothly within the valve guides and the correct
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. 2 - Removing Valve Spring
Fig. 1 - Location of Exhaust Valves
SEC. 1.2.2 Page 1
August. 1972
