JLG 80HX_HX+6_HXER ANSI Service Manual - Manual (Page 88)

SECTION 4 - BOOM & PLATFORM
4-8 – JLG Lift – 3120271
FAILURE TO DISASSEMBLE THE BOOM ASSEMBLY AND PROP-
ERLY INSPECT AND/OR REPLACE THE BOOM CHAINS AND
RELATED COMPONENTS (I.E., SHEAVES, PINS, SPROCKETS,
WEAR PADS, ETC.) COULD RESULT IN THE DAMAGE AND/OR
BREAKAGE OF THE BOOM CHAINS AND/OR RELATED COMPO-
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
Inspect boom chains for the following condition:
6. 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 toler-
ances. 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 pat-
tern, 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.
7. 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.
8. 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 this
lubricant on chains. A grade of SAE 30 or 40 weight,
non detergent motor oil should be used as a supple-
mental lubricant and a film of this oil should be con-
stantly 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.
9. 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.
10. Tight Joints: All joints in the roller chain should flex
freely. On roller chain, tight joints are usually caused
by rust/corrosion, or the inside plates “walking” off
the bushing. Limber up rusty/corroded chains (after
inspecting care fully) with a heavy application of oil
(preferably a hot oil dip). Tap inside “walking” plates
inward; if “walking” persists, replace the chain. This
type of problem is accelerated by poor lubrication
maintenance practice, and most tight joint chains
have been operated with little or no lubrication. Tight
joints on leaf chain are generally caused by:
11. Bent pins or plates.
12. Rusty joints.
13. Peened plate edges.