DETROIT DIESEL
Engine Tune-Up
EXHAUST VALVE CLEARANCE ADJUSTMENT
operating mechanism is replaced or disturbed in any
The correct exhaust valve clearance at normal engine
way, the valve clearance must first be adjusted to the
operating temperature is important for smooth,
cold setting to allow for normal expansion of the
efficient operation of the engine.
engine parts during the engine warm-up period. This
will ensure a valve setting which is close enough to the
Insufficient valve clearance can result in loss of
compression, misfiring cylinders, and eventually
specified clearance to prevent damage to the valves
when the engine is started.
burned valve seats and valve seat inserts. Excessive
v a l v e clearance will result in noisy operation,
All of the exhaust valves may be adjusted, in firing
especially in the low speed range.
order sequence, during one full revolution of the
crankshaft. Refer to the General Specifications at the
Whenever the cylinder head is overhauled, the exhaust
front of the manual for the engine firing order.
valves reconditioned or replaced, or the valve
TWO VALVE CYLINDER HEADS
4. Loosen the exhaust valve rocker arm push rod lock
nut.
5. Place a .012" feeler gage, J 9708, between the valve
stem and the rocker arm (Fig. 1). Adjust the push rod
to obtain a smooth pull on the feeler gage.
6. Remove the feeler gage. Hold the push rod with a
5 / 1 6 " wrench and tighten the lock nut with a
1/2" wrench.
7. Recheck the clearance. At this time, if the
adjustment is correct, the .010" gage will pass freely
between the end of the valve stem and the rocker arm
and the .012" gage will not pass through.
8. Check and adjust the remaining valves in the same
manner as outlined above.
Fig. 1 - Adjusting Valve Clearance (Two-Valve
Cylinder Head)
Hot Engine
Cold Engine
Maintaining normal engine operating temperature is
1. Place the speed control lever in the idle speed
particularly important when making the final valve
position. If a stop lever is provided, secure it in the no-
clearance adjustment. If the engine is allowed to cool
fuel position.
off before setting any of the valves, the clearance,
when running at full load, may become insufficient.
2. Remove the loose dirt from the valve rocker cover(s)
and remove the cover(s).
1. With the engine at normal operating temperature
(160-185F or 71-85C), recheck the exhaust valve
3. Rotate the crankshaft, manually or with the starting
clearance with feeler gage J 9708. At this time, if the
motor, until the injector follower is fully depressed on
valve clearance is correct, the .008" gage will pass
the cylinder to be adjusted.
freely between the end of the valve stem and the
rocker arm and the .010" gage will not pass through.
CAUTION: If a wrench is used on the crankshaft
Readjust the push rod, if necessary.
bolt, do not turn the engine in a left-hand
d i r e c t i o n of rotation as the bolt will be
2. After the exhaust valve clearance has been adjusted,
loosened.
check the fuel injector timing.
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