JLG 150HAX Service Manual - Manual (Page 94)

SECTION 4 - BOOM & PLATFORM
4-14 – JLG Lift – 3120817
Inspection Procedure
BOOM CHAINS ARE TO BE INSPECTED AT TIME OF NEXT BOOM
OVERHAUL AND WHEN DEEMED NECESSARY BY MACHINE OWNER.
INSPECTION INTERVAL SHOULD NOT EXCEED 500 HOURS OF
MACHINE OPERATION.
Inspect boom chains for the following conditions:
1. Wear: Always inspect that segment of chain that
operates over a sheave. As the chain flexes over the
extend/retract sheaves, joints and plate edges very
gradually wear. Chain “stretch” can be measured
using a manufacturers wear scale or steel tape.
When chains have elongated 3% they must be
removed and replaced. Refer to Table 4-1, Chain
Stretch Tolerance for proper chain specifications
and allowable stretch tolerances. Peening and wear
of chain plate edges are caused by sliding over a
chain worn contact face of a sheave, or unusually
heavy loads. All of the above require replacement of
the chain and correction of the cause. Chain side
wear, noticeable when pin heads and outside plates
show a definite wear pattern, is caused by misalign-
ment of the sheave/chain anchors and must be cor-
rected promptly. Do not repair chains; if a section of
chain is damaged, replace the entire chain set.
2. Lubrication: One of the most important but often
overlooked factors is adequate lubrication. In addi-
tion to reducing internal friction, maintaining a film of
oil on all chain surfaces will inhibit rusting and corro-
sion. This is important as corrosion of highly
stressed, hardened steel chain components can
cause a major reduction in the load capacity of leaf
chain and result in link plate cracking.
NOTE: The need for lubrication can be determined by the
presence of rust on the exposed portions of chain.
3. Rust and Corrosion: Rust and corrosion will cause
a major reduction in the load carrying capacity of the
chain, because these are primary reasons for side
plate cracking. The initial lubrication at the factory is
applied in a hot dip tank to assure full penetration
into the joint. Do not steam clean or degrease
chains. At time of chain installation, factory lube
must be supplemented by a maintenance program
to provide a film of oil on the chains at all times. If
chains are corroded, they must be inspected, espe-
cially the outside plates, for cracks in-line with the
pins. If cracks are found, replace the chain; if no
cracks are discovered, lubricate the chains by dip-
ping in heated oil, and reinstall on the machine.
Keep chains lubricated.
4. Fatigue Cracks: Fatigue is a phenomenon that
affects most metals, and is the most common cause
of chain plate failures. Fatigue cracks are found
through the link holes, perpendicular (90 degrees)
from the pin in-line position. Inspect chains carefully
after long time use and heavy loading for this type of
crack. If any cracks are discovered, replace all
chains, as seemingly sound plates are on the verge
of cracking. Fatigue and ultimate strength failures on
JLG Lifts are incurred as a result of severe abuse as
design specs are well within the rated lifting capacity
of these chains.