JLG 680S Service Manual - Manual (Page 144)

SECTION 3 - CHASSIS & TURNTABLE
3-96 – JLG Lift – 3121234
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 3-54.,
Swing Bearing Tolerance Boom Placement. (Sheet 1
of 2), using a magnetic base dial indicator, measure
and record the distance between the swing bearing
and turntable. See Figure 3-57., Swing Bearing Tol-
erance Measuring 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 3-55.,
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 3-57., Swing Bearing Tol-
erance Measuring Point.
3. If a difference greater than 0.057 in. (1.40 mm) is
determined, the swing bearing should be replaced.
4. If a difference less than 0.057 in. (1.40 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 LIFT-
ING 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 Removal
1. 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.
2. Attach an adequate support sling to the boom and
draw all slack from sling. Prop or block the boom if
feasible.
3. From inside turntable, remove mounting hardware
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.
4. Tag and disconnect the hydraulic lines from the fit-
tings on the top of the rotary coupling. Use a suit-
able container to retain any residual hydraulic fluid.
Immediately cap lines and ports.
5. Attach suitable overhead lifting equipment to the
base of the turntable weldment.
6. 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 bearing upon
installation. Remove the bolts and washers which
attach the turntable to the bearing inner race. Dis-
card the bolts.
7. 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 3-56. Swing Bolt Feeler Gauge Check.
Figure 3-57. Swing Bearing Tolerance Measuring Point.