JLG 15/20MSP Service Manual - Manual (Page 102)

SECTION 5 - MAST COMPONENTS
5-12 – JLG Lift – 3121231
Cylinder Disassembly
(See Figure 5-4.)
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 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 particularly 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
event that an unacceptable condition occurs, the head
should be replaced.
Piston
Visually inspect the outside surface for scratches or pol-
ishing. Deep scratches are unacceptable. Polishing indi-
cates uneven loading and when this occurs, the diameter
should be checked for out-of-roundness. If out-of-round-
ness exceeds 0.007", this is unacceptable. Check the con-
dition of the dynamic seals and bearings looking
particularly for metallic particles embedded in the bearing
and in the piston seal surface. Remove the seals and
bearings. Damage to the seal grooves, particularly on the
sealing surfaces, is unacceptable. In the event that an
unacceptable condition occurs, the piston should be
replaced.
Tube Assembly
Visually inspect the inside bore for scratches and pits.
There should be no scratches or pits deep enough to
catch the fingernail. Scratches that catch the fingernail but
are less than 0.5 inch long and primarily in the circumfer-
ential direction are acceptable provided they cannot cut
the piston seal. The roughness of the bore should be
between 10 and 20 μ inches RMS. Significant variation
(greater than 8 μ inches difference) are unacceptable. In
the event that an unacceptable condition occurs, the tube
assembly should be repaired or replaced.