JLG 4017RS Service Manual - Manual (Page 76)

Boom
3-36 3614RS, 4017RS
Cracked Plates
Inspect the chains very carefully, front and back as well
as side to side, for any evidence of cracked plates. If any
one crack is discovered, the chain should be replaced in
its entirety.
It is important, however to determine the cause of the
crack before installing a new chain so the condition
does not repeat itself.
The types of cracks are:
• Fatigue Cracking -
Fatigue cracks (1) are a
result of repeated cyclic
loading beyond the
chain’s endurance limit.
• Stress Corrosion
Cracking - The outside
link plates are
particularly
susceptible to stress
corrosion cracking (2).
• Corrosion Fatigue Cracking - Corrosion fatigue
cracks are very similar to fatigue cracks in
appearance. Corrosion fatigue is the combined
action of an aggressive environment and cyclic
stress.
Other Modes of Failure
• Ultimate Strength Failure -
These types of failures are
caused by overloads far in
excess of the design load.
Either fractured plates (3) or
enlarged holes (4) can occur. If
either of these failures occurs,
the chain should be replaced
immediately.
• Tight Joints -
All joints in
the chain
should flex
freely. Tight
joints (5)
resist flexing.
If the problem is caused by dirt or foreign substance
packed in the joints, clean and lubricate thoroughly
before re-installing the chain.
If the problem is caused by corrosion and rust or bent
pins, replace the chain.
3.15.4 Expose Chains for Inspection
c. Retract Chain
1. Park the machine on a firm, level surface. Place the
transmission in (N) NEUTRAL, engage the park brake
switch and raise the boom to a horizontal (level)
position.
2. Fully extend the boom until the retract chain is taut.
Shut the engine OFF.
The retract chain will be visible for inspection with the
machine in this state.
While doing the chain inspection, check all chain clevis ends
for distortion or cracking and sheaves for bearing wear or
grooving from the chain.
If during the inspection, if any chain is found to be damaged
or stretched, the chain must be replaced. It is recommended
that when any chain is replaced, that all the chains and
clevises be replaced at the same time.
d. Extend Chains
The extend chains are only partially visible through the rear
of the boom with all the sections retracted. It is possible to
see a section of the extend chain as the boom is slowly
extended. If there is ANY question that one or both extend
chains are damaged, the extend chains should be removed,
inspected and replaced if necessary.
Refer to Section 3.15, “Boom Extend and Retract Chains -
3614RS & 4017RS.”
Note: DO NOT attempt to repair a chain. Replace a stretched
or damaged chain with a new part. Always replace both the
chain and the clevis. It is recommended that when any chain is
replaced, that all chains and clevis’ be replaced at the same
time.
MZ1467
1
MZ1468
2
MZ1469
MZ1470
3
4
MZ1471 5