JLG 19AMI (3120758) Service Manual - Manual (Page 33)

SECTION 2 - SERVICE PROCEDURES
3120758 – JLG Lift – 2-19
2.9 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.
Cylinder Removal
1. Disconnect power source. (Remove the DC power
pack/charger assembly from back of mast, if so
equipped).
2. Remove ground control (pump) cover.
3. Disconnect the hydraulic lines at the pump.
4. Using suitable lifting equipment, lay machine down
horizontal onto the back of mast to allow access to
the bottom of the machine. (Preferably on an ele-
vated work surface capable of supporting the full
weight of the machine).
5. Slide (extend) the mast out the top about 2 ft. to 3 ft.
to allow access to the cylinder attach setscrew on
the attach block at the top of mast section-2.
6. Remove the cylinder attach setscrew from the attach
block on top of mast section-2. (Lowest set of
sheaves).
7. Remove the protective mast cylinder/hydraulic line
cover plate from the base frame under the mast.
NOTE: (Use a container to catch the hydraulic oil from cylin-
der and hydraulic lines in next step, discard oil).
8. Remove the hydraulic lines from the mast cylinder.
9. Original Design Cylinder: Remove the one (1) 5/
16" bolt securing the cylinder to the cylinder mount
and the four (4) 1/2" bolts securing the cylinder
mount to the mast section-1 side rails.
New Design Cylinder: Remove the snap-ring from
either end of the cylinder mount pin running through
the cylinder valve block. While supporting the cylin-
der remove the mounting pin.
NOTE: In the following step the mast cylinder mount will be
shimmed tight in the mast.
10. Remove the cylinder mast mount from the mast.
NOTE: In the following step the mast cylinder may be tight in
the cylinder attach block at the top of the mast.
11. Pull the mast cylinder out of the mast.
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.
Lift Cylinder Component Inspection
Cylinder Rod
There should be no scratches or pits deep enough to
catch the fingernail. Pits that go to the base metal are
unacceptable. Scratches that catch the fingernail but are
not to the base metal, less than 0.5 inch long and primarily
in the circumferential direction are acceptable provided
they cannot cut the rod seal. Chrome should be present
over the entire surface of the rod and the lack thereof is
unacceptable. In the event that an unacceptable condition
occurs, the rod should be repaired or replaced.
Cylinder Head
Visually inspect the inside bore for scratches or polishing.
Deep scratches are unacceptable. Polishing indicates
uneven loading and when this occurs, the bore should be
checked for out-of-roundness. If out-of-roundness exceed
0.007", this is unacceptable. Check the condition of the
dynamic seals (wiper, rod seals) looking particulary for
metallic particles embedded in the seal surface. It is nor-
mal to cut the static seal on the retaining ring groove upon
disassembly. Remove the rod seal, static o-ring and
backup and rod wiper. Damage to the seal grooves, par-
ticularly on the sealing surfaces, is unacceptable. In the