HOISTS MLC300 SERVICE/MAINTENANCE MANUAL
5-44
Published 11-22-17, Control # 257-02
Maintenance
At least once weekly, inspect and test the block-up limit
switches as follows.
1. Lower the boom and jib onto blocking at ground level
and carefully inspect the following items.
a. Inspect each limit switch lever and actuating lever
(see Figure 5-25
) for freedom of movement. Apply
one-half shot of grease to the fitting on the actuating
lever. Wipe away any excess grease.
b. Inspect each weight (see Figure 5-24
) for freedom
of movement on the load line.
c. Inspect each weight, each chain, each shackle, and
each connecting pin (see Figure 5-24
) for excessive
or abnormal wear. Make sure the cotter pins for the
shackles are installed and spread.
d. Inspect the entire length of the electric cables for
damage.
e. Make sure that the electric cables are clear of all
moving parts in the boom and jib and that the cables
are securely fastened to the boom and jib.
f. Make sure that all cables and terminating plugs are
securely fastened.
2. Test the block-up limit controls for proper operation with
the engine running using either of the following methods:
• Boom and Jib Lowered: Manually lift each weight—
one at a time. The corresponding load drum must
not operate in the up direction, and the boom/luffing
hoist must not operate in the down direction.
• Boom and Jib Raised: Slowly hoist each load block
and weight ball—one at a time—against the weight.
When the chain goes slack, the corresponding load
drum must stop hoisting, and the boom/luffing hoist
must not operate in the down direction.
Adjustment
See Figure 5-25 for the following procedure.
Lower the boom and jib onto blocking at ground level and
adjust each limit switch as follows.
1. Adjust the tension of the spring (2) by adjusting the
eyebolt and nuts (3). The spring tension must be just
enough to lift the weight of the chain and rotate the
actuating lever (7) up when the weight is lifted.
2. Loosen the setscrew (4) in the limit switch lever (8) so
the lever is free to rotate.
3. Manually lift the weight to allow the actuating lever to
rotate up.
4. Hold the actuating lever at Dimension A.
5. Hold the limit switch roller (6) against the actuating lever
while performing step 6
.
6. Slowly turn the limit switch shaft (5) clockwise until the
limit switch clicks open and hold.
7. Securely tighten the setscrew in the limit switch lever.
8. Test the limit switch for correct operation. Repeat the
adjustment steps until the block-up limit operates
correctly.
CAUTION
Prevent Damage!
To prevent two-blocking from occurring, do not operate
the crane until cause for improper operation and all
hazardous conditions have been found and corrected.
CAUTION
Avoid Sheave Damage!
Use extreme care testing the block-up limit controls when
the boom and jib are raised. If the block-up limit control
fails to stop the load, immediately stop the load by moving
the drum control handle to OFF or by applying the drum
working brake. Otherwise, two-blocking may occur.
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