JLG 4017 Service Manual - Manual (Page 117)

8.17 4017
Hydraulic System
5. Attach a suitable sling to an appropriate lifting device
and to the cylinder. Make sure the device used can
actually support the cylinder.
6. Remove the lock bolt and/or any retaining clips
securing the cylinder pins. Remove the cylinder pins.
7. Remove the cylinder.
8. Wipe up any hydraulic fluid spillage in, on, near and
around the machine, work area and tools.
a. General Cylinder Disassembly
1. Clean the cylinder with a suitable cleaner before
disassembly. Remove all dirt, debris and grease
from the cylinder.
2. Clamp the barrel end of the cylinder in a soft-jawed
vise or other acceptable holding equipment if
possible.
IMPORTANT: 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.
IMPORTANT: 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.
IMPORTANT: 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.
IMPORTANT: 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 149-204° C (300-400° F) 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.
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. Escaping
hydraulic fluid under pressure can penetrate the
skin, causing death or serious injury.
MZ0400