JLG 19BD Service Manual - Manual (Page 29)

SECTION 2 - SERVICE PROCEDURES
3121154 – JLG Lift – 2-7
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.
Tight Joints: All joints in the leaf chain should flex freely.
On leaf chain, tight joints are usually caused by rust/corro-
sion, or the inside plates “walking” off the bushing. Limber
up rusty/corroded chains (after inspecting carefully) with a
heavy application of oil (preferably a hot oil dip). Tap
inside “walking” plates inward; if “walking” persists,
replace the chain. This type of problem is accelerated by
poor lubrication maintenance practice, and most tight
joint chains have been operated with little or no lubrica-
tion. Tight joints on leaf chain are generally caused by:
a. Bent pins or plates.
b. Rusty joints.
c. Peened plate edges.
Oil rusty chains, and replace chains with bent or peened
chain components. Keep chains lubricated.
Protruding or Turned Pins: Chains operating with inade-
quate lube generate tremendous friction between the pin
and plates (pin and bushing on leaf chain). In extreme
cases, this frictional torque can actually turn the pins in
the outside press-fit plates. Inspect for turned pins, which
can be easily spotted as the “V” flats on the pin heads are
no longer in line. Replace all chains showing evidence of
turned or protruding pins. Keep chains lubricated.
Chain Anchors and Sheaves: An inspection of the chain
must include a close examination of chain anchors and
sheaves. Check chain anchors for wear breakage and
misalignment. Anchors with worn or broken fingers should
be replaced. They should also be adjusted to eliminate
twisting the chain for an even load distribution.
Inspect the sheaves, sheave bearings, sheave grooves
and pins for extreme wear, replace as necessary. A worn
sheave can mean several problems, as follows:
a. Chains too tight.
b. Sheave bearings/pin bad.
c. Bent/misaligned chains.
EXAMPLE OF MEASURING A (.50") PITCH CHAIN
24 pitches = 12 inches on a NEW chain
Maximum allowable stretch across 24 pitches (12 inches) = 12.24 inches
Table 2-3. 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
TIGHT JOINTS
ABNORMAL PROTRUSION OR
TURNED PINS