Engine Tune-Up
DETROIT DIESEL
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, efficient
cold setting to allow for normal expansion of the engine
operation of the 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
specified clearance to prevent damage to the valves
compression, misfiring cylinders, and eventually burned
when the engine is started.
valve seats and valve seat inserts. Excessive valve
clearance will result in noisy operation, especially in the
All of the exhaust valves may be adjusted, in firing order
low speed range.
sequence, during one full revolution of the crankshaft.
Refer to the General Specifications at the front of the
Whenever the cylinder head is overhauled, the exhaust
manual for the engine firing order.
valves reconditioned or replaced, or the valve
TWO VALVE CYLINDER HEADS
5.
Place a .012" feeler gage, J 9708, between the
Cold Engine
valve stem and the rocker arm (Fig. 1). Adjust the push
rod to obtain a smooth pull on the feeler gage.
1.
Place the speed control lever in the idle speed
position. If a stop lever is provided, secure it in the no-
6.
Remove the feeler gage. Hold the push rod
fuel position.
with a 5/16"wrench and tighten the lock nut with a 1/2
"wrench.
2.
Remove the loose dirt from the valve rocker
cover(s) and remove the cover(s).
7.
Recheck the clearance. At this time, if the
adjustment is correct, the .010"gage will pass freely
3.
Rotate the crankshaft, manually or with the
between the end of the valve stem and the rocker arm
starting motor, until the injector follower is fully
and the .012 " gage will not pass through.
depressed on the cylinder to be adjusted.
8.
Check and adjust the remaining valves in the
CAUTION: If a wrench is used on the crankshaft
same manner as outlined above.
bolt, do not turn the engine in a left-hand
direction of rotation as the bolt will be loosened.
Hot Engine
4.
Loosen the exhaust valve rocker arm push rod
Maintaining normal engine operating temperature is
lock nut.
particularly important when making the final valve
clearance adjustment. If the engine is allowed to cool
off before setting any of the valves, the clearance, when
running at full load, may become insufficient.
1.
With the engine at normal operating
temperature (160 -185F.), recheck the exhaust valve
clearance with feeler gage J 9708. At this time, if the
valve clearance is correct, the .008" gage will pass
freely between the end of the valve stem and the rocker
arm and the .010" gage will not pass through. Readjust
the push rod, if necessary.
2.
After the exhaust valve clearance has been
adjusted, check the fuel injector timing.
Fig. 1 - Adjusting Valve Clearance (Two-Valve
Cylinder Head)
Page 74
