JLG 120HX ANSI Service Manual - Manual (Page 27)

SECTION 2 - PROCEDURES
3120686 – JLG Lift – 2-7
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.
d. 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.
e. 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/cor-
roded chains (after inspecting carefully) 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:
1. Bent pins or plates.
2. Rusty joints.
3. Peened plate edges.
Oil rusty chains, and replace chains with bent or
peened chain components. Keep chains lubri-
cated.
f. Protruding or Turned Pins: Chains operating
with inadequate lube generate tremendous fric-
tion between the pin and plates (pin and bush-
ing on roller chain). In extreme cases, this
frictional torque can actually turn the pins in the
outside press-fit plates. Inspect for turned pins,
which can be easily spotted as the “V” flats on
the pin heads are no longer in line. Replace all
chains showing evidence of turned or protruding
pins. Keep chains lubricated.
g. Stress Corrosion Cracking: The outside link
plates, which are heavily press-fitted to the pins,
are particularly susceptible to stress corrosion
cracking. Like fatigue cracks, these initiate at the
point of highest stress (aperture) but tend to
extend in an arc-like path, often parallel to the
rolling grain of the material.
Also, more than one crack can often appear on a
link plate. In addition to rusting, this condition
can be caused by exposure to an acidic or caus-
tic medium or atmosphere. Stress corrosion is
an environmentally assisted failure. Two condi-
tions must be present - corrosive agent and
static stress. In the chain, static stress is present
at the aperture due to the press fit pin. No cycle
motion is required and the plates can crack dur-
ing idle periods. The reactions of many chemical
agents (such as battery acid fumes) with hard-
TIGHT JOINTS
ABNORMAL PROTRUSION OR
TURNED PINS