Jlg 40H Service Manual User Manual download pdf (Page 26)

SECTION 2 - PROCEDURES

2-6 – JLG Lift – 3120240

pin in-line position. Inspect chains carefully

after long time use and heavy loading for

this type of crack. If any cracks are

discovered, 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 lifting capacity of these chains.

Tight Joints: All joints in the roller chain should

flex freely. On roller chain, tight joints are usually

caused by rust/corrosion, or the inside plates

“walking” off the bushing. Limber up rusty/cor-

roded chains (after inspecting care fully) 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 lubrication. Tight joints

on leaf chain are generally caused by:

1. Bent pins or plates.

2. Rusty joints.

3. Peened plate edges.

Oil rusty chains, and replace chains with bent or

peened chain components. Keep chains lubri-

cated.

Protruding or Tur ned Pi ns: Chains operating

with inadequate lube generate tremendous fric-

tion between the pin and plates (pin and bushing

on roller 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.

Stress Corrosion Cracking: The outside link

plates, which are heavily press-fitted to the pins,

are particularly susceptible to stress corrosion

cracking. Like fatigue cracks, these initiate at the

point of highest stress (aperture) but tend to

extend in an arc-like path, often parallel to the roll-

ing grain of the material.

Also, more then one crack can often appear on a

link plate. In addition to rusting, this condition can

be caused by exposure to an acidic or caustic

medium or atmosphere. Stress corrosion is an

environmentally assisted failure. Two conditions

must be present - corrosive agent and static

stress. In the chain, static stress is present at the

aperture due to the press fit pin.

No cycle motion is required and the plates can

crack during idle periods. The reactions of many

chemical agents (such as battery acid fumes) with

hardened metals liberate hydrogen which attacks

and weakens the metal grain structure.

Chain Anchors, Sheaves and Pins: An inspec-

tion of the chain must include a close examination

of chain anchors, sheaves and pins. Check chain

anchors for wear breakage and misalignment.

Anchors with worn or broken fingers should be

replaced. They should also be adjusted to elimi-

nate twisting the chain for an even load distribu-

tion.

Sheaves should be inspected for worn flanges,

which would indicate misalignment, and wear on

the outside diameter of the sheave. A worn

sheave can mean several problems, as follows:

1. Chains too tight.

2. Sheave bearings/pin bad.

3. Bent/misaligned chains.

2.7 WEAR PADS.

1. Shim up wear pads within 1/16 in. (1.59 mm) toler-

ance between wear pad and adjacent surface.

2. Replace wear pads when worn within 1/8 in. (3.18

mm) of threaded insert.

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Jlg 40H Service Manual User Manual Page 26

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