JLG 20VP (3120728) Service Manual - Manual (Page 41)

SECTION 2 - SERVICE PROCEDURES
3120728 – JLG Lift – 2-23
2.8 HYDRAULIC LIFT CYLINDER -
REMOVAL, INSPECTION AND REBUILD
HYDRAULIC CYLINDERS ARE DESIGNED TO HOLD HYDRAULIC
FLUID UNDER HIGH PRESSURE. BE SURE ALL APPROPRIATE
MEASURES ARE TAKEN TO RELIEVE RESIDUAL PRESSURE IN
THE CYLINDER BEFORE DISCONNECTING LINES.
Lift Cylinder Removal
Removal of the hydraulic lift cylinder without removing the
mast from the machine requires laying the machine on it’s
back (hood side) with the platform end on top.
1. Remove the hood from the rear of the machine.
2. Disconnect and remove the batteries from the
machine, to prevent acid leakage.
3. Seal the vented cap on the hydraulic fluid reservoir
by removing the cap, covering the hole with a few
layers of plastic wrap or equivalent, then install and
tighten the cap over the plastic wrap.
NOTE: If a quick-change platform is attached to the machine
remove the platform to help reduce the weight of the
machine during machine lay back.
4. Use a forklift truck or overhead crane and carefully
lay the machine on it’s back, place a support under
the mast end. (See Figure 2-16.)
5. Manually extend the mast assembly approximately
two (2) feet, to allow access to the sheave wheel-
anchor block at the top of mast section-2.
6. Remove the set screw securing the lift cylinder rod
to the sheave wheel anchor block at the top of mast
section-2.
7. Under the base assembly remove the four (4) bolts
attaching the PHP bar actuator assembly to the lift
cylinder mount. Secure the assembly out of the way.
8. Carefully disconnect and cap the extend and return
lines and fittings from the lift cylinder, drain any
hydraulic fluid into a container.
9. Remove the bolt securing the lift cylinder to the cyl-
inder mount.
10. Remove the four (4) bolts, washers and nuts attach-
ing the cylinder mount to the base frame. Remove
the mount and lay aside.
11. At the bottom of mast section 2, slide the lift cylinder
assembly out and place on a suitable work surface.
Cylinder Disassembly
1. Before disassembling the cylinder, clean away all
dirt and foreign substances from openings, particu-
larly the head area.
NOTE: Always protect the chrome surface of the cylinder
rod during assembly and disassembly. Any damage
to this surface will require replacement of the rod.
2. Extend the rod until the piston bottoms out against
the cylinder head.
3. Compress the head retraining ring enough to allow
the the cylinder head to be removed.
4. Carefully slide the head/rod/piston assembly out of
the cylinder tube. A gentle tap on the head assembly
may be required to remove the head from the cylin-
der tube.
5. Place the head/rod/piston assembly on a surface
that will not damage the chrome.
6. Remove the piston locknut and separate the piston
from the rod.
7. Slide the head off the rod from the piston end.
NOTE: When removing the old seals use only blunt tools, be
sure there are no sharp edges that may damage the
seal grooves during removal. Scratching the groove
may cause by-pass.
8. Remove and discard all old seals.
Figure 2-16. Machine Positioned for Cylinder
Removal.
SUPPORT
MAST
AVOID DAMAGE TO
CONTROLS IN
THIS AREA