JLG 4017RS Service Manual - Manual (Page 73)

3-33 3614RS, 4017RS
Boom
3.15 BOOM EXTEND AND RETRACT
CHAINS - 3614RS & 4017RS
3.15.1 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. Refer to the Service Manual for the
proper procedure. 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 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 vehicle.
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.
3.15.2 Inspection Guidelines - 3614RS
a. Retract Chain
1. Park the machine on a firm, level surface, raise the boom
to a horizontal (level) position, place the transmission in
(N) NEUTRAL, engage the park brake switch.
2. Fully extend the boom until the retract chain is taut.
Shut the engine off.
3. The retract chain will be visible for inspection with the
vehicle in this state.
4. While doing the chain inspection, check all chain clevis
ends, pins for distortion or cracking and sheaves for
bearing wear or grooving from the chain.
b. Extend Chains
1. Park the machine on a firm, level surface, raise the boom
to a horizontal (level) position, place the transmission in
(N) NEUTRAL, engage the park brake switch.
2. Fully retract the boom. Shut the engine off.
3. Both extend chain clevises and pins will be visible for
inspection with the vehicle in this state.
4. Limited visual inspection of the extend chains is
possible. For complete extend chain inspection, the
extend chains must be removed from the boom. For
extend chain removal, refer to Section 3.4.3, “Extend
Chain Removal,” and Section 3.4.4, “Extend Chain
Installation.”
5. Inspect the extend and retract chains every 250 hours of
operation.
6. Inspect the chains for the following conditions:
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.