JLG 150HAX ANSI Service Manual - Manual (Page 95)

SECTION 4 - BOOM & PLATFORM
3120679 – JLG Lift – 4-15
5. 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:
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 lubricated.
6. Protruding or Turned Pins: Chains operating with
inadequate lube generate tremendous friction
between the pin and plates (pin and bushing 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.
7. 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 high-
est stress (aperture) but tend to extend in an arc-like
path, often parallel to the rolling grain of the material.
Also, more then one crack can often appear on a
link plate. In addition to rusting, this condition can
be caused by exposure to an acidic or caustic
medium or atmosphere. Stress corrosion is an envi-
ronmentally assisted failure. Two conditions 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 during idle periods. The
reactions of many chemical agents (such as battery
acid fumes) with hardened metals liberate hydrogen
which attacks and weakens the metal grain struc-
ture.
TIGHT JOINTS
ABNORMAL PROTRUSION OR
TURNED PINS
ARC-LIKE CRACKED PLATES
(STRESS CORROSION)