JLG G12-55A Service Manual - Manual (Page 59)

3-25 G10-55A, G12-55A
Boom
• Maintain a total boom section clearance (5) of
0.070 - 0.130 in (1,78 - 3,30 mm) both the horizontal
and vertical directions.
• The length of the wear pad bolt depends on the
number of shims, spacers and washers being used.
• The thickness of each threaded wear pad insert is
0.312 in (7,92 mm)(A).
• The bolt length should be determined by measuring
the distance from the face of the insert to the face of
the boom (B) including any spacer, shim(s) and
washer(s).
• Bolt thread engagement in the wear pad insert
should be 0.275 ± 0.040 in (6,98 ± 1,0 mm).
• One or two hardened washers are to be used on
each wear pad bolt except where noted otherwise.
DO NOT use more than two hardened washers.
• Use only one hardened washer if mounting bolts are
recessed.
• Wear Pad Bolt Torque:
3/8 - 24 Bolt, 32 - 37 lb-ft (43 - 50 Nm)
3/8 - 24 Hollow Bolt, 15 - 17 lb-ft (20 - 23 Nm)
1/2 - 20 Bolt, 76 - 86 lb-ft (103 - 116 Nm)
1/2 - 20 Hollow Bolt, 45 - 50 lb-ft (61 - 68 Nm)
• Torque wear pad bolts after shimming is completed.
• Lubricate the face and pockets of each wear pad
after being installed.
Boom Section Wear Pad Pathway Lubrication:
• Clean and lightly grease all wear pad pathways with
Mystik Tetrimoly grease.
6. Clean and lightly grease the hose carrier guide bar
pathways with Mystik Tetrimoly grease.
3.12 BOOM EXTEND AND RETRACT
CHAINS
3.12.1 Boom Chain Inspection
Under normal operating conditions the boom chains will
need to be inspected every
250 hours of operation. The
retract chains need to be exposed and inspected every
1000 hours of operation. Environmental conditions and
dynamic impulse/shock loads can drastically affect
normal operating conditions and require more frequent
inspection intervals.
Environments in which material handling vehicles
operate can vary widely from outdoor moisture to
temperature to mildly corrosive or highly corrosive
industrial atmospheres, in addition to abrasive
exposures such as sand and grit. Some effects can be
as follows:
• Moisture - Corrosive rusting reduces chain
strength by pitting and cracking.
• Temperature - Low temperature reduces chain
strength by embrittlement. Going in and out of
cold storage results in moisture from
condensation.
• Chemical Solutions or Vapors - Corrosive attack
on the chain components and/or the mechanical
connections between the chain components.
Cracking can be (and often is) microscopic.
Going from microscopic cracking to complete
failure can be either abrupt or may require an
extended period of time.
• Abrasives - Accelerated wearing and scoring of
the articulating members of the chain (pins an d
plates), with a corresponding reduction in chain
strength. Due to the inaccessibility of the bearing
surfaces (pin surfaces and plate apertures),
wear and scoring are not readily noticeable to
the naked eye.
MY5510
5 5
MY3620
A
B
WARNING
Worn pins, stretched or cracked links or corrosive
environments can cause chain failure. A chain failure
could result in uncontrolled boom movement, loss of
load or machine instability.