Engine Tune-Up
EXHAUST VALVE CLEARANCE ADJUSTMENT
Whenever the cylinder head is overhauled, the exhaust
The correct exhaust valve clearance at normal engine
valves are reconditioned or replaced, or the valve
o p e r a t i n g temperature is i m p o r t a n t for smooth,
operating mechanism is replaced or disturbed in any
efficient operation of the engine.
way. the valve clearance must first be adjusted to the
cold setting to allow for normal expansion of the
Insufficient valve clearance can result in loss of
engine parts during the engine warm-up period. This
compression, misfiring cylinders and, eventually,
will ensure a valve setting that is close enough to the
burned valve seats and valve seat inserts. Excessive
specified clearance to prevent damage to the valves
v a l v e clearance will result in noisy operation,
when the engine is started.
especially in the low speed range.
ENGINES WITH TWO VALVE CYLINDER HEADS
engine barring tool J 22582. until the injector follower
All of the exhaust valves may be adjusted, in firing
is fully depressed on the cylinder to be adjusted.
order sequence, during one full revolution of the
crankshaft. Refer to the General Specifcations at the
CAUTION: If a wrench is used on the crankshaft
front of the manual for the engine firing order.
or camshaft bolt at the front of the engine, do
not turn the engine in a left-hand direction of
rotation as the bolt will be loosened.
Exhaust Valve Clearance Adjustment (Cold
Engine)
4. Loosen the exhaust valve rocker arm push rod lock
nut.
1 . Place the governor stop lever in the no-fuel
position.
5. Place a .013" feeler gage, tool 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.
2. Clean the loose dirt from the valve rocker covers
and remove the covers. Then cover any drain cavities
6. Remove the feeler gage. Hold the push rod with a
in the cylinder head to prevent foreign material from
5/16" wrench and tighten the lock nut with a
entering.
1/2" wrench.
3. Rotate the crankshaft, with the starting motor or
7. Recheck the clearance. At this time, if the
adjustment is correct, the .011" feeler gage will pass
freely between the valve stem and the rocker arm, but
the .013" feeler gage will not pass through.
8. Check and adjust the remaining valves in the same
manner as outlined above.
Exhaust Valve Clearance Adjustment (Hot
Engine)
Maintaining normal engine operating temperature is
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.
With the engine at normal operating temperature
(160-185F or 71-85C), recheck the exhaust valve
clearance with feeler gage J 9708. At this time, if the
valve clearance is correct, the .008" feeler gage will
pass freely between the valve stem and the rocker arm,
but the .010" gage will not pass through.
Fig. 1 - Adjusting Valve Clearance
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