JLG 120-SXJ Service Manual - Manual (Page 57)

SECTION 4 - BOOM & PLATFORM
3121810 – JLG Lift – 4-9
Inspection Procedure
BOOM CHAINS TO BE INSPECTED AT TIME OF NEXT BOOM
OVERHAUL AND WHEN DEEMED NECESSARY BY MACHINE
OWNER, BUT NOT TO EXCEED 2 YEARS OF MACHINE OPERA-
TION.
1. Inspect boom chains for the following conditions:
a. 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 2-1 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 unusu-
ally 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.
b. 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 rust-
ing 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.
c. 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 lubri-
cation 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 of 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. A
grade of SAE 30 or 40 weight, non-detergent
motor oil should be used as a supplemental
lubricant and a film of this oil should be con-
stantly maintained on the surfaces and internal
joints. 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.
Figure 4-3. Typical Boom Assembly