JLG 20VP (3120728) Service Manual - Manual (Page 49)

SECTION 2 - SERVICE PROCEDURES
3120728 – JLG Lift – 2-31
Mast Assembly
(See Figure 2-18., 2-19., 2-20. & 2-21.)
1. Place mast section-1, rail (open) side up on a clean,
flat surface (preferably a table or work bench capa-
ble of supporting the weight of the entire mast
assembly). Slide mast out over end of work surface
far enough to allow access to the chain anchor
attach holes at top of mast.
2. Locate the two (2) single cable/chain assemblies.
Lay out each cable/chain assembly with anchor
block end towards mast, and threaded end away
from mast, (be certain floor surface is clean and free
of any metal chips or debris which may stick to lubri-
cated chains).
3. Insert the block anchor end into the top of mast sec-
tion-1 and secure using two (2) 3/8"-16UNC x 2-1/2"
(chain) 1-1/4" (cable) long hex head bolts, flatwash-
ers and nuts for each attach block. Place a flat-
washer under bolt head and nut.
NOTE: When sliding mast sections together, be careful not
to scratch or score the anodized finish in the slide
pad channels.
4. Locate mast section-2, carefully slide mast section-2
closed rail into section-1 open rail. Slide sections
together until ends are even.
NOTE: Do not attach mast slide pads and shims to mast
sections before assembling sections. If assembled in
this manner, due to the tight fit of the slide pads in
the slide pad channels, the anodized finish could be
removed from the receiving mast’s slide pad chan-
nels.
5. Insert slide pads into the slide pad channels at bot-
tom end of mast between section-1 and -2, (one on
each side of the mast), with beveled surface facing
out towards section-1.
6. Thread slide pad attaching bolts, (two (2) 1/4"-
20UNC x 3/8" long hex head bolts, place a flat
washer under head of each bolt), through holes in
mast section-2 inside rail, into the slide pad inserts.
Thread in enough to hold pad in place.
7. Shim slide pads using the following steps:
NOTE: Always use the an even amount of shim material
behind slide pads on both sides of the mast rails.
This will keep mast sections centered in rail chan-
nels and prevent any distortion of the mast section.
a. Use two shim pieces per slide pad, a thick one
and a thin one.
b. Start with a total thickness of approximately a
.025" thick shim and a .055" thick shim.Slide
shims into place between slide pad and mast
rail. Tighten the slide pad mounting bolts, be
sure there are no air gaps (on flat side of slide
pad) between shims, shim and mast or shim and
slide pad when tightened.
c. All mast sections are to be shimmed to provide a
measurable gap between the slide pad (beveled
side) and mast channel of 0.012" to 0.025" per
side.
d. When mast slide pads are shimmed properly,
the mast sections should be able to slide in
channel by hand.
8. Insert slide pads into the slide pad channels (top of
mast) between section-1 and -2, (one on each side
of the mast), with beveled surface facing in towards
section-2.
9. Thread slide pad attaching bolts, (two (2) 1/4"-
20UNC x 3/8" long hex head bolts, place a flat
washer under head of each bolt), through holes in
mast section-1 outside rail (top of mast) and into the
slide pad inserts. Thread in enough to hold pad in
place.
10. Shim per instructions in step 7.
NOTE: If hydraulic cylinder needs to be extended, the pro-
tective caps on the extend and return ports will need
to be removed. Be careful not to nick or scour rod
surface when extending, also catch any oil draining
out of cylinder to avoid spillage onto work area.
11. Locate the hydraulic lift cylinder, slide the lift cylinder
into the closed rail side of mast section-2 with rod
end to top and port end to bottom of mast. Cylinder
should extend out of mast on both ends. Return
tube should be on right side when facing bottom of
mast assembly.
NOTE: Top of cylinder assembly steps 12 and 13 applies to
20VP only. For 10VP & 15VP continue to step 14.
12. Locate chain assembly #444 (single anchor block
with two narrow chains). Lay out chain assembly
with anchor block end towards mast, (be certain
floor surface is clean and free of any metal chip or
debris which may stick to lubricated chains).
13. Insert hydraulic cylinder rod end into chain assem-
bly #444, anchor block. Secure cylinder rod to
anchor block with a 1/4"-28UNF x .50" long - Type C
setscrew. Coat threads with blue Loctite # 242
before assembly.
NOTE: When sliding mast sections together, be careful not
to scratch or score the anodized finish in the slide
pad rails.
a. Locate mast section-3, carefully slide section-3
closed rail into section-2 open rail. Slide sec-
tions together until ends are even. Locate one
(1) of the chain/cable anchor plates (one with
threaded holes horizontally aligned to outside of