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ENGINE DIVISION SERVICE MANUAL
TM 5-4210-230-14&P-1
ENGINE
the valve gear length increases, as caused by lower engine
temperatures, the plunger spring keeps all the valve gear
parts in contact, increasing the clearance volume under the
plunger. At the same time oil is immediately fed past the
check valve, thus maintaining correct length under all
conditions. This keeps the valve gear operating at no-lash.
With this predetermined leakage, is impossible for the no-lash
lifter to hold the engine valve open when it should be closed.
When the lifter body is on the base circle of the cam
and the engine valve is closed, the only force tending to hold
the valve open is from the light plunger spring, which
obviously is much lower than the valve spring load. The only
additional force tending to push the plunger upward results
from pressure of the lubricating oil but its effect is negligible
since it is controlled and only acts on the small plunger area.
During shutdown periods of the engine, one or more
valves are always in the lifted position thus imposing the full
valve spring load on the plunger. This causes oil to leak out
of the compression chamber through the clearance space.
When the engine is again started, the particular valve that
was in the open position returns to its seat and the plunger is
immediately forced upward by its spring. Oil from the supply
chamber is again fed into the clearance volume under the
plunger so that in a very few cycles, the valve gear is
operating on a solid hydraulic oil column.
II.
When to Service
A.
Loud clacking, light clicking or intermittent noise is
attributed to a lifter.
Dirt, chips, varnish, etc., generally cause only a few
units to become inoperative at any one time.
Aeration caused by high or low oil level air leaks into
the oil pump suction line, etc., result in all lifters
becoming noisy. The cause of aeration must be
corrected before the lifters will again operate quietly.
Small metal chips lodging between the plunger and
the cylinder tend to prevent free movement. Since
loads
during the lift portion of the cycle are
relatively high, the plunger is forced downward and
the very light plunger spring has insufficient force to
move the plunger back to normal operating position.
After a few lift cycles with metal chips between the
plunger and cylinder, the plunger finally reaches a
position (usually plunger bottomed) where there is
excessive lash in-the valve train with resulting noisy
operation.
The type of varnish, resulting from a mixture of
permanent antifreeze and oil, is very "tacky" and,
particularly when cold, will prevent free movement of
the plunger. The resulting action is the same as that
caused by a chip in the clearance space. The entire
engine must be cleaned and the cause of the leakage
corrected.
Varnish of the type resulting from fuels and
lubricants, unless excessive amounts are created by
poor
crankcase
ventilation
or
extremely
bad
lubricants, seldom causes sticking in the lifter.
However, if such deposits do form and cause trouble,
it is then necessary to correct crankcase ventilation,
lubricant or fuel.
1.
Loud clacking noise is the result of excessive lash
and indicates that:
a.
The plunger is stuck below its normal operating
position, probably plunger bottomed and in this case,
the lifter must be disassembled and cleaned of dirt
and varnish.
b. The check valve may not be sealing due to dirt or a
damaged seat, which also necessitates cleaning and
inspection.
c. Oil may contain sufficient air, which is compressible,
to permit collapse or partial plunger movement
beyond its normal operating position. It is necessary
to locate and correct the cause of aeration. Just
servicing the lifter will not help.
2.
Light clicking type noise indicates that the plunger is
operating only slightly below its normal position as
the result of:
a. Slight leakage by the check valve or plunger. If the
noise is persistent, the lifter must be removed,
cleaned and checked.
CGES-210 Page 45
PRINTED IN UNITED STATES OF AMERICA
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