JLG G6-42A Service Manual - Manual (Page 160)

Hydraulic System
8-26 G6-42A, G9-43A, G10-43A
Note: Avoid using excessive force when clamping the
cylinder in a vise. Apply only enough force to hold the
cylinder securely. Excessive force can damage the
cylinder tube.
3. If applicable, remove the counterbalance valve from
the side of the cylinder barrel.
Note: DO NOT tamper with or attempt to adjust the
counterbalance valve cartridge. If adjustment or
replacement is necessary, replace the counterbalance
valve with a new part.
4. Extend the rod as required to allow access to the
base of the cylinder.
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 from the tube. A considerable amount of force
will be needed to remove the head gland. 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.
6. Carefully pull the rod assembly along with the head
gland out of the cylinder barrel.
7. 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.
8. Remove the set screw from the piston head.
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.
9. Remove the piston head from the rod and carefully
slide the head gland off the end of the rod.
10. 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.
c. 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.
d. 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.
WARNING
Significant pressure may be trapped inside the
cylinder. Exercise caution when removing a
counterbalance valve or a pilot-operated check valve
from a cylinder.