JLG 740A, Service And Maintenance Manual

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SECTION 3 - CHASSIS & TURNTABLE
3121160 – JLG Lift – 3-47
Wear Tolerance
1. From the underside of the machine, at rear center,
with the main boom fully elevated and fully retracted,
and tower boom stowed, as shown in Figure 3-34.
Swing Bearing Tolerance Boom Placement, using a
magnetic base dial indicator, measure and record
the distance between the swing bearing and turnta-
ble. See Figure 3-37., Swing Bearing Tolerance Mea-
suring Point.
2. At the same point, with the main boom at horizontal
and fully extended, and the tower boom fully ele-
vated and fully retracted as shown in Figure 3-35.,
Swing Bearing Tolerance Boom Placement.(Sheet 2
of 2). Using a magnetic base dial indicator, measure
and record the distance between the swing bearing
and turntable. See Figure 3-37., Swing Bearing Tol-
erance Measuring Point.
3. If a difference greater than 0.079 in. (2.00 mm) is
determined, the swing bearing should be replaced.
4. If a difference less than 0.079 in. (2.00 mm) is deter-
mined, and any of the following conditions exist, the
bearing should be removed, disassembled, and
inspected for the following:
a. Metal particles in the grease.
b. Increased drive power required.
c. Noise.
d. Rough rotation.
5. If bearing inspection shows no defects, reassemble
and return to service.
THE SWING BEARING IS ONE OF THE MOST CRITICAL POINTS ON
AN AERIAL LIFT. IT IS HERE THAT THE STRESSES OF LIFTING
ARE CONCENTRATED, AT THE CENTER OF ROTATION. BECAUSE
OF THIS, PROPER MAINTENANCE OF THE SWING BEARING
BOLTS IS A MUST FOR SAFE OPERATION.
Swing Bearing Replacement
1. Removal.
a. From Ground Control station, operate the boom
adequately to provide access to frame opening
to rotary coupling.
NEVER WORK BENEATH THE BOOM WITHOUT FIRST ENGAGING
BOOM SAFETY PROP OR PROVIDING ADEQUATE OVERHEAD
SLING SUPPORT AND/OR BLOCKING.
b. Attach an adequate support sling to the boom
and draw all slack from sling. Prop or block the
boom if feasible.
c. From inside turntable, remove mounting hard-
ware which attach rotary coupling retaining yoke
brackets to turntable.
HYDRAULIC LINES AND PORTS SHOULD BE CAPPED IMMEDI-
ATELY AFTER DISCONNECTING LINES TO AVOID THE ENTRY OF
CONTAMINANTS INTO THE SYSTEM.
d. Tag and disconnect the hydraulic lines from the
fittings on the top of the rotary coupling. Use a
suitable container to retain any residual hydrau-
lic fluid. Immediately cap lines and ports.
e. Attach suitable overhead lifting equipment to the
base of the turntable weldment.
f. Use a suitable tool to scribe a line on the inner
race of the swing bearing and on the underside
of the turntable. This will aid in aligning the bear-
ing upon installation. Remove the bolts and
washers which attach the turntable to the bear-
ing inner race. Discard the bolts.
g. Use the lifting equipment to carefully lift the com-
plete turntable assembly from the bearing.
Ensure that no damage occurs to the turntable,
bearing or frame-mounted components.
Figure 3-36. Swing Bolt Feeler Gauge Check.
Figure 3-37. Swing Bearing Tolerance Measuring Point.