JLG 680S, Service And Maintenance Manual

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SECTION 3 - CHASSIS & TURNTABLE
3121234 3-139
Wear Tolerance
1. From the underside of the machine, at rear center, with
the main boom fully elevated and fully retracted, as
shown in Figure 3-75., 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 3-79., Swing
Bearing Tolerance Measuring Point.
2. At the same point, with the main boom at horizontal
and fully extended, as shown in Figure 3-76., 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 3-79., Swing Bearing Tolerance Measuring Point.
3. If a difference greater than 0.079 in. (2.00 mm) is deter-
mined, 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 Removal
1. From Ground Control station, operate the boom ade-
quately 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 BLOCK-
ING.
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 IMMEDIATELY AFTER DIS-
CONNECTING LINES TO AVOID THE ENTRY OF CONTAMINANTS INTO THE SYS-
TEM.
4. Tag and disconnect the hydraulic lines from the fittings
on the top of the rotary coupling. Use a suitable con-
tainer 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 turnta-
ble. This will aid in aligning the bearing upon installa-
tion. Remove the bolts and washers which attach the
turntable to the bearing inner race. Discard the bolts.
7. Use the lifting equipment to carefully lift the complete
turntable assembly from the bearing. Ensure that no
damage occurs to the turntable, bearing or frame-
mounted components.
Figure 3-78. Swing Bolt Feeler Gauge Check.
Figure 3-79. Swing Bearing Tolerance Measuring Point.