JLG G12-55A Service Manual - Manual (Page 138)

Hydraulic System
8-22 G10-55A, G12-55A
Note: Protect the finish of the rod at all times. Damage
to the surface of the rod can cause seal failure.
5. Using a pin spanner wrench, unscrew the head
gland (4) from the tube (2). A considerable amount
of force will be needed to remove the head gland.
6. Carefully slide the head gland down along the rod
toward the rod eye, away from the cylinder barrel.
Note: When sliding the rod and piston assembly out of
the barrel, prevent the threaded end of the barrel from
damaging the piston. Keep the rod centered within the
barrel to help prevent binding.
7. Carefully pull the rod assembly (3) along with the
head gland (4) out of the cylinder barrel.
8. Fasten the rod eye in a soft-jawed vise, and place a
padded support under and near the threaded end of
the rod to prevent any damage to the rod.
9. Remove the set screw from the piston head (5).
10. If equipped, remove the piston head (5) mounting
nut (6).
Note: It may be necessary to apply heat to break the
bond of the sealant between the piston and the rod
before the piston can be removed.
Some cylinder parts are sealed with a special organic
sealant and locking compound. Before attempting to
disassemble these parts, remove any accessible seals
from the area of the bonded parts. Wipe off any hydraulic
oil, then heat the part(s) 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 for removal
while the parts are still hot. The sealant often leaves a
white, powdery residue on threads and other parts, which
must be removed by brushing with a soft brass wire brush
prior to reassembly.
11. Remove the piston head (5) from the rod (3) and
carefully slide the head gland (4) off the end of the
rod.
12. Remove all seals, back-up rings and o-rings from the
piston head and all seals, back-up rings and o-rings
from the head gland.
Note: The head gland bearing will need to be inspected
to determine if replacement is necessary.
DO NOT attempt to salvage cylinder seals, sealing rings
or o-rings. ALWAYS use a new, complete seal kit when
rebuilding hydraulic components. Consult the parts
catalog for ordering information.
b. Cylinder Cleaning Instructions
1. Discard all seals, back-up rings and o-rings. Replace
with new items from seal kit to ensure proper
cylinder function.
2. 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
or parts, it can be removed by using a soft brass wire
brush. Wipe clean with Loctite
® Cleaner prior to
reassembly.
8.8.2 Cylinder Inspection
1. Inspect internal surfaces and all parts for wear,
damage, etc. If the inner surface of the cylinder
barrel does not display a smooth finish, or is scored
or damaged in any way, replace the barrel.
2. Remove light scratches on the piston, head gland,
rod or inner surface of the cylinder barrel with a 400-
600 grit emery cloth. Use the emery cloth in a rotary
motion to polish out and blend the scratch(es) into
the surrounding surface.
3. Check the piston rod assembly for run-out. If the rod
is bent, it must be replaced.
c. General Cylinder Assembly Instructions
1. Use the proper tools for specific installation tasks.
Clean tools are required for installation.
2. Install new seals, back-up rings and o-rings on the
piston and new seals, back-up rings, o-rings and
bearing on the head gland.
Note: The extend/retract cylinder has a spacer that
MUST be installed over the rod
AFTER the head gland
and BEFORE the piston head.
3. Fasten the rod eye in a soft-jawed vise, and place a
padded support under and near the threaded end of
the rod to prevent any damage to the rod.
Note: Protect the finish on the cylinder rod at all times.
Damage to the surface of the rod can cause seal failure.
4. Lubricate and slide the head gland over the cylinder
rod. Install the piston head on to the end of the
cylinder rod. Loctite
® and install the set screw in the
piston head. Refer to Section 8.8.5, “Cylinder Torque
Specifications” for torque specifications for the
piston head and the set screw.