JLG 120HX Service Manual - Manual (Page 30)

SECTION 2 - PROCEDURES
2-8 – JLG Lift – 3120819
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.
2.7 WEAR PADS
Shim up wear pads to within 1.6 mm (1/16 in.) tolerance
between wear pad and adjacent surface.
Replace wear pads when worn within 3.2 mm (1/8 in.) of
threaded insert.
2.8 DRIFT TEST
NOTE: It is recommended that the machine be shut down in
the test mode for at least one hour prior to beginning
the drift test. This will allow the oil temperature in the
cylinder to stabilize with the ambient temperature.
Thermal expansion or retraction of the hydraulic oil
can greatly affect cylinder movement.
Telescope Cylinder
NOTE: Switches referenced in this procedure are located on
the Ground Control Panel.
1. Activate hydraulic system, properly set extendable
axles and position boom in stowed position; adhere
to all safety precautions.
BEFORE RAISING AND EXTENDING BOOM, ENSURE THAT
AREAS ABOVE AND BELOW BOOM AND PLATFORM AND AHEAD
OF PLATFORM ARE CLEAR OF ALL OBSTRUCTIONS AND PER-
SONNEL.
2. Position LIFT control switch to UP and hold until
boom reaches horizontal.
3. Position TELESCOPE control switch to OUT and
hold until boom extends approximately 1.2 meter (4
feet); measure from end of base section to end of
mid section.
4. Position LIFT control switch to UP and hold until
boom reaches maximum elevation. Shut down
engine.
5. Tag and carefully disconnect the hydraulic lines to
the telescope cylinder at control valve.
6. Observe oil flow from cylinder lines. Oil leaking from
extend port hose indicates a leaking counterbalance
valve. Oil leaking from retract port hose indicates
leakage by cylinder piston.
7. Leave boom elevated in test position for approxi-
mately one hour.
BEFORE LOWERING BOOM, ENSURE THAT AREAS BELOW
BOOM AND PLATFORM ARE CLEAR OF ALL PERSONNEL AND
OBSTRUCTIONS.
8. Position LIFT control switch to DOWN and hold until
boom reaches horizontal; check boom length
against measurement. If boom has retracted more
than 2.5 cm (1 inch) and oil is leaking around rod-
end of telescope cylinder (check with light and
inspection mirror), seals are defective and require
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 (14 in.) or
28 pitches
1.07 cm (0.42 in.)
1.00 in. (2.54 cm)
pitch
36 cm (14 in.) or
14 pitches
1.07 cm (0.42 in.)
1.75 in. (4.45 cm)
pitch
36 cm (14 in.) or 8
pitches
1.07 cm (0.42 in.)
2.00 in. (5.08 cm)
pitch
36 cm (14 in.) or 7
pitches
1.07 cm (0.42 in.)
ARC-LIKE CRACKED PLATES
(STRESS CORROSION)