Boom Chain Inspection - JLG sky trak mmv Service Manual

2.13.20

Boom Chain Inspection

250
MS21702
WARNING:
cracked links or corrosive environments can
cause chain failure. A chain failure could result
in uncontrolled boom movement, loss of load
or vehicle instability and could cause death or
serious injury and/or property damage.
Under normal operating conditions the boom chains will
need to be inspected every 250 hours of operation. Envi-
ronmental conditions and dynamic impulse/shock loads
can drastically affect normal operating conditions.
Environments in which material handling vehicles
operate can vary widely from outdoor moisture to mildly
corrosive or highly corrosive industrial atmospheres, in
addition to abrasive exposures such as sand and grit.
• Moisture - Corrosive rusting reduces chain
strength by pitting and cracking.
• Temperature - Low temperature reduces chain
strength by making the metal brittle. 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 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.
Model MMV Rev. 12/04
General Information, Specifications and Maintenance
MM2130
Worn pins, stretched or
Dynamic shock loading 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 vehicle.
Environmental conditions and load cycles make it
impossible to predict chain life. Each specific application
should be evaluated, based on the degree of exposure,
the areas of possible operation and the types of load
cycles.
A chain replacement schedule should be established to
prevent chain failure. This schedule can be established
by frequent inspection. Based on the observations, the
frequency of inspection can be changed.
This inspection procedure development should go on
until a projected time of replacement can be predicted. A
chain by its very nature and exposure should be
considered an expendable item and a safe chain
replacement schedule established.
The boom chain's normal life expectancy can be
expressed as a maximum percent of elongation. This is
generally 3% of pitch. As the chain flexes back and forth
over the sheave, the bearing joints (pins and inside link
plates) gradually incur wear due to articulation.
Inspection Guidelines
1. Park the vehicle on level ground. Place the travel
select lever in [N] NEUTRAL, place the neutral lock
lever in the [N] NEUTRAL LOCK position, engage
the parking brake switch and raise the boom to a
horizontal (level) position.
2. Fully extend the boom until the extend chain is taut.
Shut the engine off.
The extend chains will be visible for inspection with
the vehicle in this state. The retract chain can be vi-
sually inspected, at the rear of the boom, as the boom
is slowly retracted.
While doing the chain inspection, check all chain
clevis ends for distortion or cracking and sheaves for
bearing wear or grooving from the chain.
3. Inspect the chains for the following conditions:
2.61