Two exhaust valves are provided for each cylinder.
(Fig. 1). The valve heads are heat treated and ground
Exhaust Valve Maintenance
to the proper seat angle and diameter. The valve stems
are ground to size and hardened at the end which
Efficient combustion in the engine requires that the
contacts the rocker arm.
exhaust valves he maintained in good operating
condition. Valve seats must be true and unpitted to
The exhaust valve stems are contained within exhaust
assure leakproof seating, valve stems must work freely
valve guides which are pressed into the cylinder head
and smoothly within the valve guides and the correct
Exhaust valve seat inserts (Fig. 2), pressed into the
Proper maintenance and operation of the engine is
cylinder head, permit accurate seating of the exhaust
important to long valve life.
valves under varying conditions of temperature and
temperatures should be maintained between 160-185° F
materially prolong the life of the cylinder head. The
(71-85° C). Low operating temperatures (usually due to
exhaust valves are ground to a 30° seating angle while
extended periods of idling or light engine loads) result in
the exhaust valve seat inserts are ground to a 31°
incomplete combustion, formation of excessive carbon
deposits and fuel lacquers on valves and related parts.
and a greater tendency for lubricating oil to sludge.
The exhaust valve springs are held in place by the valve
spring caps and tapered two-piece valve locks.
Unsuitable fuels may also cause formation of deposits
on the valves, especially when operating at low
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
When carbon deposits, due to partially burned fuel, build
ports are uncovered.
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.
Fig. 1. Location of Exhaust Valves (Two-Valve
Fig. 2. Assembly of Exhaust Valves and Guides