JLG G6-42A Service Manual - Manual (Page 68)

Boom
3-30 G6-42A, G9-43A, G10-43A
Cracked Plates
Inspect 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 (9) 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 (10).
• 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 (1) or
enlarged holes (2) 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 (3)
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.
3.11.4 Chain Lubrication
After inspection and before being returned to service,
chains must be lubricated. Refer to Section 2.5, “Fluid
and Lubricant Capacities.”
The lubricant must penetrate the chain joint to prevent
wear. Applying lubricant to the external surfaces will
prevent rust, but the chains should be articulated to
make sure the lubricant penetrates to the working
surfaces between the pins and links.
To prepare the chain for lubrication, the chain plates
should be brushed with a stiff brush or wire brush to
clear the space between the plates so that lubricant can
penetrate to the working surfaces.
Lubricant may be applied with a narrow paint brush or
directly poured on, but the chain should be well flooded
with lubricant and the boom should be extended and
retracted to be sure that the lubricant penetrates to the
working surfaces. All surplus lubricant should be wiped
away from the external surfaces. DO NOT use a solvent
for this wiping operation.
Regular application of lubricant is necessary to make
sure that all working surfaces are adequately lubricated.
In extremely dusty conditions, it may be necessary to
lubricate the chains more often.
Lubrication of chains on vehicles working consistently in
extreme hot or cold conditions requires special
consideration. It is important that a reputable lubrication
specialist, a local JLG Distributor or the vehicle distributor
be consulted for guidance.
MZ1467
9
MZ1468
10
MZ1469
MZ1470
1
2
MZ1471 3