JLG 450AJ ANSI Service Manual - Manual (Page 42)

SECTION 2 - PROCEDURES
2-24 – JLG Lift – 3120749
Wear Tolerance
1. With the boom positioned over the side of the
machine, the Upper Boom horizontal with telescope
fully extended and Mid/Lower Boom stowed, using a
magnetic base dial indicator, measure and record
the distance between the swing bearing and turnta-
ble.
2. At the same point, with the boom positioned over
the side of the machine, the Upper Boom fully ele-
vated and the Mid/Lower Boom fully elevated, using
a magnetic base dial indicator, measure and record
the distance between the swing bearing and turnta-
ble.
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.
a. Metal particles in the grease.
b. Increased drive power.
c. Noise.
d. Rough rotation.
5. If bearing inspection shows no defects, reassemble
bearing and return to service.
Replacement of Swing Bearing
Removal of the swing bearing is as follows:
1. Attach an adequate support sling to the boom and
draw all slack from sling. Prop or block the boom if
feasible.
2. Tag and disconnect hydraulic lines running through
center of turntable and frame. Use a suitable con-
tainer to retain any residual hydraulic fluid. Cap lines
and ports.
3. Attach suitable overhead lifting equipment to the
base of turntable weldment.
4. 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 bolts, nuts and washers which
attach the turntable to the bearing inner race. Dis-
card nuts and bolts.
5. 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.
6. Carefully place the turntable on a suitably supported
trestle.
7. Use a suitable tool to scribe a line on the outer race
of the swing bearing and the frame. This line will aid
in aligning the bearing upon installation. Remove the
bolts and washers which attach the outer race of the
bearing to the frame. Discard the bolts. Use suitable
lifting equipment to remove the bearing and rotation
box assembly from the frame; move to a clean, suit-
ably supported work area.
8. Remove the two capscrews securing the bearing to
the rotation box to separate the two for inspection.
Installation of the swing bearing is as follows:
1. Install bearing to rotation box with two capscrews,
so that fill plug of bearing is as close to gear as bolt
pattern will allow. Do not tighten capscrews.
2. Line up high spot (blue) of bearing with center tooth
of worm gear. Set backlash to 0.008 - 0.010 inch
(0.20 - 0.25 mm). Tighten capscrews as shown in
Figure 2-21., Swing Bearing Torque Sequence.
SWING
BEARING
FRAME REF.
TURNTABLE REF.
MEASURING
POINT
Figure 2-20. Swing Bearing Tolerance Measuring
Point