JLG sky trak mmv Service Manual page 451

7. Fasten the trunnion end of the rod in a soft-jawed
vise and put a padded support below and near the
threaded end of the rod to help prevent damage to
the rod.
8. Remove the locking inserts (8) from the head gland
threads. Pry or drill out the insert as required. DO
NOT damage the head gland threads. A new locking
insert will be required for reassembly.
9. Remove the setscrew (9) from the piston (7). The
setscrew is used to provide a secondary lock on the
piston.
10. Remove the piston (7) from the rod spacer (10) and
rod (5). The piston was installed with Loctite #243
and torqued to 350-450 lb/ft (475-610 Nm).
Note: It may be necessary to apply heat to break the
bond of the sealant between piston (7) and the rod (5)
before the piston can be removed. Some parts of cylin-
ders are sealed with a special organic sealant and lock-
ing compound.
Before attempting to disassemble these parts, remove
any accessible seals from the area of the bonded joint.
Wipe off any hydraulic oil and heat the joint uniformly to
break the bond. A temperature of 300-400° F (149-204° C)
will destroy the bond. Avoid overheating or the parts may
become distorted or damaged. Apply sufficient torque or
pressure for removal while the parts are still hot.
Breakdown of sealant will leave a white, powdery resi-
due on threads and parts. Clean the residue away with a
soft brass wire brush prior to reassembly, and wipe with
Loctite "T" cleaner before reinstallation.
11. Remove the rod spacer (10).
12. Remove both precision wearbands (11), piston
seal (12) and square ring (13) from the piston (7).
13. From within the piston (7), remove the back-up
rings (14) and the small o-ring (15).
14. Remove the o-ring (16), back-up ring (17) and o-ring
(18) from the head gland (6). Remove them from the
rod (5).
15. Remove the head gland (6) from the rod.
16. From within the head gland (6), remove one of the
precision wearbands (19), the buffer seal (25),
another precision wear band (19), the deep Z-seal
with back-up (20) and the sealed outside diameter
heavy-duty rod wiper (21).
Model MMV Rev. 12/04
c. Extend/Retract Cylinder Cleaning
1. Remove all hydraulic fluid, dirt and debris from the
inner surface of the cylinder tube (2).
2. Discard all seals, back-up rings, o-rings, etc.
Replace with new items from a complete seal kit (22)
to help ensure proper cylinder function.
3. Clean all metal parts with an approved cleaning
solvent such as trichlorethylene. Carefully clean
cavities, grooves, threads, etc.
Note: If a white, powdery residue is present on threads
and parts, it can be removed. Clean the residue away
with a soft brass wire brush prior to reassembly, and
wipe with Loctite "T" cleaner before reinstallation.
d. Extend/Retract Cylinder Inspection
1. Inspect internal surfaces and all parts for wear,
damage, etc. If the inner surface of the tube (2) does
not display a smooth finish, or is scored or damaged
in any way, replace the tube. Often, dirty hydraulic
fluid causes failure of internal seals and damage to
the smooth surface within the tube.
2. Remove slight scratches on the piston, rod, or inner
surface of the tube with very fine grit emery cloth.
Use the emery cloth in a rotary motion to polish out
and blend the scratch(es) into the surrounding
surface.
3. Clean parts with trichlorethylene.
4. Check that the rod (5) is straight. If it is bent, install a
new rod.
e. Extend/Retract Cylinder Assembly
Note: Follow Section 9.14.3, General Cylinder Assem-
bly Instructions.
1. Install a new back-up ring (14), small o-ring (15) and
another back-up ring (14) into the forward end of the
piston (7).
2. Install the square ring (13), piston seal (12) and both
precision wearbands (11) onto the piston (7).
Hydraulic System
9.153