3-25
BOOM CHAIN ADJUSTMENT
Study Illustrations 1,2 and 3 to understand the chain adjustment procedure. Proper adjustment
is critical at time of boom assembly or scheduled maintenance.
Initial adjustment:
Retract boom completely. The 4
th
stage extension and retraction chains
set the position of the 4
th
stage relative to the 3
rd
stage. As shown in Illustration 1, ½” (13mm)
clearance must be held between the 4
th
stage tip and 3
rd
stage tip. To increase this distance,
loosen the retraction adjustment and tighten the extension adjustment. To decrease this dis-
tance, loosen the extension adjustment and tighten the retraction adjustment.
Final adjustment
: Extend boom completely while horizontal, then slightly retract the boom to
let the chains relax. Measure the inside chain drape at the center of the rear 3
rd
stage and 2
nd
stage windows as shown in Illustration 3. See arrows in the windows for measuring locations.
Measure the outside chains at midspan. Snug the 4
TH
stage extension and retraction chains
until the chain tightness allows the dimensions of approximately 1” and 5” as shown in Illustra-
tion 3. Also snug the 2
nd
and 3
rd
stage compensation chains to the dimensions of 1 1/8” (29mm)
and 3 7/8” (98mm) as shown. Assure that the drape in each pair of chains is matched so each
chain carries its share of the load. Run boom in and out a few times and recheck all of the
above dimensions. After proper settings retighten the adjustment lock nuts.
The numbers “3” shown in the small windows on the bottom of the 2
nd
stage and base boom
show the adjustment is about midrange. These numbers run from 1 to 6 in 1” (25mm) incre-
ments. Numbers in these windows are approximate adjustment and cannot be used for final
adjustment. Important are the dimensions stated above taken at the large side windows.
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