Lull 944E-42 Service Manual - Manual (Page 45)

3-15 944E-42
Boom
• Abrasives - Accelerated wearing and scoring of
the articulating members of the chain (pins and
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.
Following are some examples of dynamic shock loading
which can impose abnormal loads above the endurance
limit of a leaf chain.
• High velocity movement of load, followed by
sudden, abrupt stops.
• Carrying loads in suspension over irregular
surfaces such as railroad tracks, potholes, and
rough terrain.
• Attempting to “inch” loads which are beyond the
rated capacity of the machine.
The above load cycles and environmental conditions
make it impossible to predict chain life. It is therefore
necessary to conduct frequent inspections until
replacement life can be predicted.
The boom chain’s normal life expectancy can be
expressed as a maximum percent of elongation. This is
generally 3%. As the chain flexes back and forth over the
sheave, the bearing joints (pins and inside link plates)
gradually incur wear due to articulation.
3.4.2 Inspection Guidelines
1. Park the machine on a firm, level surface, raise the
boom to a horizontal (level) position, place the
transmission control lever in (N) NEUTRAL, engage
the park brake switch.
2. Fully extend the boom until the extend chain is taut.
Shut the engine off.
3. The extend chains will be visible for inspection with
the machine in this state.
4. While doing the chain inspection, check all chain
clevis ends for distortion or cracking and sheaves for
bearing wear or grooving from the chain.
5. Inspect the retract chains every 1000 hours of
operation.
6. Inspect the chains for the following conditions:
Edge Wear
Check the chain for wear on the link plate edges
caused by running back and forth over the sheave.
The maximum reduction of material should not
exceed 5%. Measure and compare to a normal link
plate height by measuring a portion of chain that
does not run over the sheave. If the measured plate
height (1) is 5% less than the normal plate height
(2), discard and replace the chain.
Elongation
It is important to measure the chain in the section
that moves over the sheaves because it receives the
most frequent articulation. Measuring the chain near
its clevis terminals could give an inaccurate reading.
The ends of the chains, near the clevis terminal, will
not have flexed as frequently, if at all, as the middle
of the chains.
It is best to measure in 12 pin increments from pin
center to pin center. For example, if the links are one
inch from pin center to pin center, the distance
should be 12 in (305 mm). If the links are 3/4 in
(9,5 mm) apart, the distance after 12 pins should be
9 in (229 mm).
If the distance measured (3) is 3% greater than the
normal length (4), discard and replace the chain.
MZ1463
2 1
MY1360
3
4