JLG M4069 ANSI Service Manual - Manual (Page 78)

SECTION 4 - HYDRAULICS
4-6 – JLG Lift – 3121122
4.11 CYLINDER REPAIR
NOTE: The following are general procedures that apply to
all of the cylinders on this machine. Procedures that
apply to a specific cylinder will be so noted.
Disassembly
DISASSEMBLY OF THE CYLINDER SHOULD BE PERFORMED ON
A CLEAN WORK SURFACE IN A DIRT FREE WORK AREA.
1. Operate the hydraulic power source and extend the
cylinder. Shut down and disconnect the power
source. Adequately support the cylinder rod, if nec-
essary.
2. If applicable, remove the cartridge-type holding
valve and fittings from the cylinder port block. Dis-
card o-rings.
3. Place the cylinder barrel into a suitable holding fix-
ture.
4. To aid in realignment, mark cylinder head and barrel
with a center punch.
5. Using a suitable spanner wrench, loosen the span-
ner nut retainer and remove the spanner nut from
the cylinder barrel.
6. Attach a suitable pulling device to the cylinder rod
port block or cylinder rod end, as applicable.
EXTREME CARE SHOULD BE TAKEN WHEN REMOVING THE CYL-
INDER ROD, HEAD, AND PISTON. AVOID PULLING THE ROD OFF-
CENTER, WHICH COULD CAUSE DAMAGE TO THE PISTON AND
CYLINDER BARREL SURFACES.
7. With the barrel clamped securely, apply pressure to
the rod pulling device and carefully withdraw the
complete rod assembly from the cylinder barrel.
8. Using suitable protection, clamp the cylinder rod in
a vise or similar holding fixture as close to the piston
as possible.
9. If applicable, loosen and remove the nut which
attaches the piston to the rod, then remove the pis-
ton from the rod.
10. If applicable, loosen and remove the cap screw(s)
securing the tapered bushing to the piston.
11. Insert the capscrew(s) in the threaded holes in the
outer piece of the tapered bushing. Progressively
tighten the cap screw(s) until the bushing is loose
on the piston, then remove the bushing from the pis-
ton.
12. Screw the piston counter-clockwise, by hand, and
remove the piston from the cylinder rod.
13. Remove and discard the piston o-rings, back-up
rings, guidelock rings and hydrolock seals.
14. If applicable, remove the piston spacer from the rod.
15. Remove the rod from the holding fixture. Remove
the cylinder head and retainer plate from the rod.
Figure 4-1. Barrel Support
Figure 4-2. Cap Screw Removal
Figure 4-3. Rod Support