JLG M600 Service Manual - Manual (Page 120)

SECTION 4 - BOOM & PLATFORM
4-10 – JLG Lift – 3121813
4.3 PLATFORM ROTATOR (PRIOR TO S/N
0300130810)
Theory of Operation
See Figure 4-9., Platform Rotator Assembly - Cutaway
Fluid entering Port P2 under pressure will bear on the pis-
ton (4) and force the piston sleeve (3) upwards. The left-
handed spline of the piston sleeve (3) will combine with
the right- handed spline of the shaft (2A) and cause rapid
counter-clockwise rotation of the shaft and flange (2B)
(looking down). Fluid entering Port P1 will reverse this
rotation.
Displacement and torque are identical for clockwise and
counterclockwise rotation.
The shaft (2A) is integral with the shaft flange (2B) and
bearing tube (2C). The shaft is supported radially by the
large upper radial bearing (19) and the lower radial bear-
ing (18). Axially, the shaft is separated from the housing by
the upper and lower thrust rings (20). The end cap (5) is
adjusted for axial clearance and locked in position by cap
screws (7).
Disassembly and Inspection
Place on a clean workbench with room to place the inter-
nal parts as they are removed. Remove all hydraulic fit-
tings Loosen cap screws(7) and unscrew locknut (6) and
end cap (5). The shaft is now free to move up and out of
engagement with the piston sleeve (3). Note the orienta-
tion between the spline teeth (see Figure II), as this will
greatly simplify actuator timing upon reassembly.
After removing the shaft, the piston sleeve and the piston
assembly can now be moved down and out of the hous-
ing. Remove all seals and bearings from their grooves,
except static piston seals (9) and (11). These seals gener-
ally do not require replacement. Clean all parts thoroughly
and inspect for wear. A small amount of wear in the spline
teeth will have little effect on the actuator strength. New
spline sets are manufactured with a backlash of about
0.005” (0.127 mm) per mating set. After long service, a
backlash of about 0.015” (0.381 mm) per set may still be
acceptable in most cases, depending on the required
accuracy of the application.
Item (1) is the integral housing and ring gear. Check the
ring gear for wear and weld damage to the pins. Inspect
the cylinder bore for wear and scratches. The surface fin-
ish should be 32 RMS or better; re-hone if necessary. The
radial bearings (18) and (1 9) and the piston bearings (17)
should have a maximum radial clearance of 0.006” (0.152
mm). A clearance in excess of 0.008” (0.203 mm) requires
replacement of the bearings. Rough and grooved shaft
journals require shaft replacement.
Assembly and Testing
Wash all parts thoroughly in cleaning solvent and blow
dry. Coat all sealing and working surfaces with a good
grade hydraulic oil. Install seals and bearings in the piston
sleeve, piston, shaft, and end cap. The lips of the exclu-
sion seals (16) face outward, and the lips of the high pres-
sure seals face inward.
Place the actuator in a vertical position, install the piston
sleeve (3) in timed relation to the housing, applying firm
pressure as the new seals and bearings enter the housing
and become compressed by the housing chamber.
DO NOT MISALIGN THE SLEEVE TOO MUCH ANY ONE WAY, AS IT
WILL MAR THE CYLINDER BORE). THE TIMING MARKS (THE
SMALL PUNCH MARKS ON THE FACE OF EACH GEAR), MUST BE
ALIGNED FOR PROPER SHAFT ORIENTATION. REFER TO FIGURE
4-8., TIMING MARKS.
1. Integral Housing & Ring Gear
2. Shaft
3. Piston Sleeve
Figure 4-8. Timing Marks