JLG 120-SXJ ANSI Service Manual - Manual (Page 63)

SECTION 4 - BOOM & PLATFORM
3121105 – JLG Lift – 4-11
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-
ened metals liberate hydrogen which attacks
and weakens the metal grain structure.
h. Chain Anchors and Sheaves: An inspection of
the chain must include a close examination of
chain anchors and sheaves. Check chain
anchors for wear breakage and misalignment.
Anchors with worn or broken fingers should be
replaced. They should also be adjusted to elimi-
nate twisting the chain for an even load distribu-
tion.
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.
4.3 WEAR PADS
Shim up wear pads to within 1/16 in. (1.6 mm) tolerance
between wear pad and adjacent surface.
Replace wear pads when worn within 1/8 in. (3.2 mm) of
threaded insert.
4.4 LIMIT SWITCH ADJUSTMENTS
Boom Limit Switch
The boom limit switch is located on the left side of the
base section of the boom. The switch will activate when
the boom is extended past a set point with the axles
retracted. When activated, the switch cuts out Telescope
Out and Lift Up. Adjust the limit switch to trip at 10 feet (3
meters) of boom extension.
Horizontal Cut-Out Switch
The horizontal cut-out switch is located on the right side of
the boom at the boom pivot pin. When activated, the
switch cuts out the High Engine, High Drive and 2 Speed
functions. Adjust the switch to activate when the boom
reaches horizontal.
ARC-LIKE CRACKED PLATES
(STRESS CORROSION)
Table 4-1. Chain Stretch Tolerance
CHAIN SIZE
PIN TO PIN
MEASUREMENT
ALLOWABLE
STRETCH 14 IN.
SPAN
0.50 in. (1.27 cm)
pitch
14 in. (36 cm) or
28 pitches
0.42 in. (1.07 cm)
0.625 in.
(1.59 cm) pitch
15 in. (38 cm) or
24 pitches
0.45 in. (1.14 cm)
0.75 in.
(1.91 cm) pitch
15 in. (38 cm) or
20 pitches
0.45 in. (1.14 cm)
1.00 in. (2.54 cm)
pitch
14 in. (36 cm) or
14 pitches
0.42 in. (1.07 cm)
1.75 in. (4.45 cm)
pitch
14 in. (36 cm) or 8
pitches
0.42 in. (1.07 cm)
2.00 in. (5.08 cm)
pitch
14 in. (36 cm) or 7
pitches
0.42 in. (1.07 cm)