JLG 40H Service Manual - Manual (Page 25)

SECTION 2 - PROCEDURES
3120240 – JLG Lift –
2-5
NENTS. DAMAGE AND/OR BREAKAGE OF THESE ITEMS COULD
RESULT IN UNCONTROLLED EXTENSION OR RETRACTION OF THE BOOM ASSEMBLY AND COULD CAUSE SERIOUS INJURY OR
DEATH TO PERSONNEL OPERATING THE JLG BOOM LIFT.
Inspection Procedures.
5. Inspect boom chains for the following condition:
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 mea-
sured using a manufacturers wear scale or steel
tape. When chains have elongated 3% they must
be removed and replaced. Refer to Table 1 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
misalignment of the sheave/chain anchors and
must be corrected promptly. Do not repair chains;
if a section of chain is damaged, replace the
entire chain set.
Lubrication: One of the most important but often
overlooked factors is adequate lubrication. In
addition to reducing internal friction, maintaining
a film of oil on all chain surfaces will inhibit rusting
and corrosion. This is important as corrosion of
highly stressed, hardened steel chain compo-
nents 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.
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 lubrica-
tion at the factory is applied in a hot dip tank to
assure full penetration into the joint. Do not steam
clean or degrease this lubricant on chains. A
grade of SAE 30 or 40 weight, non detergent
motor oil should be used as a supplemental lubri-
cant and a film of this oil should be constantly
maintained on the surfaces and internal joints. At
time of chain installation, factory Lube must be
supplemented by a maintenance program to pro-
vide a film of oil on the chains at all times. If
chains are corroded, they must be inspected,
especially 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 dipping in heated oil, and reinstall on
the machine. Keep chains lubricated.
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
Figure 2-1. Typical Three Section Boom Assembly.