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

SECTION 2 - SERVICE PROCEDURES
2-2 – JLG Lift – 3120728
apply pressure to the outer race. If the bearing is to be
installed on a shaft, apply pressure to the inner race.
Gaskets
Check that holes in gaskets align with openings in the
mating parts. If it becomes necessary to hand-fabricate a
gasket, use gasket material or stock of equivalent material
and thickness. Be sure to cut holes in the right location, as
blank gaskets can cause serious system damage.
Bolt Usage and Torque Application
Use bolts of proper length. A bolt which is too long will
bottom before the head is tight against its related part. If a
bolt is too short, there will not be enough thread area to
engage and hold the part properly. When replacing bolts,
use only those having the same specifications of the origi-
nal, or one which is equivalent.
Unless specific torque requirements are given within the
text, standard torque values should be used on heat-
treated bolts, studs, and steel nuts, in accordance with
recommended shop practices. (See Figure 1-1.)
Hydraulic Lines and Electrical Wiring
Clearly mark or tag hydraulic lines and electrical wiring, as
well as their receptacles, when disconnecting or removing
them from the unit. This will assure that they are correctly
reinstalled.
Hydraulic System
Keep the system clean. If evidence of metal or rubber par-
ticles is found in the hydraulic system, drain and flush the
entire system.
Disassemble and reassemble parts on clean work sur-
face. Clean all metal parts with non-flammable cleaning
solvent. Lubricate components, as required, to aid assem-
bly.
Lubrication and Servicing
Components and assemblies requiring lubrication and
servicing are shown in the Lubrication Chart, (See Figure
1-2.). Service applicable components with the amount,
type, and grade of lubricant recommended in this manual,
at the specified intervals. When recommended lubricants
are not available, consult your local supplier for an equiva-
lent that meets or exceeds the specifications listed.
Batteries
Clean batteries, using a non-metallic brush and a solution
of baking soda and water. Rinse with clean water. After
cleaning, thoroughly dry batteries and coat terminals with
an anti-corrosion compound.
Mast Chain Inspection Procedure
MAST CHAINS TO BE INSPECTED AND LUBRICATED EVERY
THREE MONTHS.
Inspect mast chains for the following conditions:
Wear: Always inspect that segment of chain that operates
over a sheave. As the chain flexes over the sheaves, joints
and plate edges very gradually wear. Chain “stretch” can
be measured using a manufacturers wear scale or steel
tape. When chains have elongated 3% they must be
removed and replaced. Refer to Table 2-1 for proper chain
specifications and allowable stretch tolerances. Peening
and wear of chain plate edges are caused by sliding over
a chain worn contact face of a sheave, or unusually heavy
loads. All of the above require replacement of the chain
and correction of the cause. Chain side wear, noticeable
when pin heads and outside plates show a definite wear
pattern, is caused by misalignment of the sheave/chain
anchors and must be corrected promptly. Do not repair
chains; if a section of chain is damaged, replace the entire
chain set.
Rust and Corrosion: Rust and corrosion will cause a
major reduction in the load carrying capacity of the chain,
because these are primary reasons for side plate crack-
ing. The initial lubrication at the factory is applied in a hot
dip tank to assure full penetration into the joint. Do not
steam clean or degrease chains. At time of chain installa-
tion, factory lube must be supplemented by a mainte-
nance program to provide a film of oil on the chains at all
times. If chains are corroded, they must be inspected,
especially the outside plates, for cracks in-line with the
pins. If cracks are found, replace the chain; if no cracks
are discovered, lubricate the chains by dipping in heated
oil, and reinstall on the machine. Keep chains lubricated.
Fatigue Cracks: Fatigue is a phenomenon that affects
most metals, and is the most common cause of chain
plate failures. Fatigue cracks are found through the link
holes, perpendicular (90 degrees) from the pin in-line
position. Inspect chains carefully after long time use and
heavy loading for this type of crack. If any cracks are dis-
covered, replace all chains, as seemingly sound plates
are on the verge of cracking. Fatigue and ultimate
strength failures on JLG Lifts are incurred as a result of
severe abuse as design specs are well within the rated lift-
ing capacity of these chains.
Table 2-1. Chain Stretch Tolerance
Chain Size
Pin to Pin
Measurement
Allowable Stretch
.50" pitch 12" or 24 pitches .24 in./12 in. span
.625 pitch 15" or 24 pitches .30 in./15 in. span