JLG 80HX_HX+6_HXER Service Manual - Manual (Page 30)

SECTION 2 - PROCEDURES
2-8 – JLG Lift – 3120863
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.
8. Chain Anchors, Sheaves and Pins: An inspection
of the chain must include a close examination of
chain anchors, sheaves and pins. Check chain
anchors for wear breakage and misalignment.
Anchors with worn or broken fingers should be
replaced. They should also be adjusted to eliminate
twisting the chain for an even load distribution.
Sheaves should be inspected for worn flanges, which
would indicate misalignment, and wear on the outside
diameter of the sheave. A worn sheave can mean several
problems, as follows:
1. Chains too tight.
2. Sheave bearings/pin bad.
3. Bent/misaligned chains.
.
Auxiliary Boom Chains
The auxiliary boom chains are used as a safety device, to
prevent the boom from retracting in the event that an
extend chain should break. As the boom would begin to
retract, tension would be placed on the auxiliary chain,
stopping the boom and tripping a limit switch to shut
down the machine.
The auxiliary boom chain is located on top of the boom.
One end of the chain is attached to an adjustable clevis on
top of the front end of the base section, and uses belleville
washers and adjusting nuts to adjust chain tension. The
other end of the chain is attached to a fixed clevis on top
of the fly section. A limit switch is installed adjacent to the
adjustable clevis on the base section, and when tripped,
shuts down the machine. Adjust chain tension so there is
no slack in the chain and set the cam on the switch so the
switch trips when the belleville washers compress 1 to 1.3
cm.
REPLACE THE BELLEVILLE WASHERS ONCE THEY HAVE BEEN
COMPRESSED.
TIGHT JOINTS
ABNORMAL PROTRUSION OR
TURNED PINS
ARC-LIKE CRACKED PLATES
(STRESS CORROSION)
Table 2-1. Chain Stretch Tolerance
CHAIN SIZE
PIN TO PIN
MEASUREMENT
ALLOWABLE
STRETCH 14 IN.
SPAN
0.50 in. (1.27 cm)
pitch
36 cm or 28
pitches
1.07 cm
1.00 in. (2.54 cm)
pitch
36 cm or 14
pitches
1.07 cm
1.75 in. (4.45 cm)
pitch
36 cm or 8
pitches
1.07 cm
2.00 in. (5.08 cm)
pitch
36 cm or 7
pitches
1.07 cm