National Crane 600H, Service Manual

Page: 90 / 232

BOOM 600H SERVICE MANUAL
4-16
08-19-2022 Control # 092-13
Uneven pad wear of 3/32 in (2 mm) from side to side on the
wear pad would be considered excessive as well. If any of
these conditions exist, the top and bottom pads can be re
placed without complete disassembly of the boom.
Top Rear Pad Replacement
Pad maintenance on the four section can be made easier by
removal of the hoist and or removal of the hoist mounting bar
spanning the end of the 1
st
section. Additional clearance can
be achieved by loosening the large extend cables and
removing the extend cable anchor located in the 2
nd
section.
1. Retract boom completely.
2. Remove capscrews through access holes on top rear of
sections.
3. Remove wear pads, shims, and cam plates from the rear
of the boom through open hoist mount end.
4. Note all pad locations and tag accordingly.
5. Inspect pads for wear using previously mentioned
inspection criteria.
6. Assemble new wear pads with the cam plates and install
through the hoist mount end of the boom. Install
capscrews through holes in outer boom sections.The
wear pad on each side at the top/rear of the boom can
be adjusted over a range of 3/16 in (4.8 mm) by rotating,
end for end, the wear pad and plate or the wear pads
and plate independently. This is possible because the
holes in these parts are offset from the center. The holes
are 0.06 in (1.5 mm) off center in the plate and 0.03 in
(0.8 mm) off center in the wear pad. Various
combinations of rotation of these parts allow the
adjustment.
a. Adjust pads until they are within 0.03” (.8mm) off
center in the wear pad. Various combinations of
rotation of these parts allows the adjustment.
b. Torque retainer capscrews, refer to Fasteners and
Torque Values pg 1-7. Failure to properly torque
capscrews will cause loss of preload and cause
excessive side clearance between sections.
Front Bottom Pad Replacement
1. Extend boom approximately 4 ft (120 cm) out.
2. Remove cable guides and upper spacer bars from front
of boom sections
3. Loosen and remove hex nuts on retract cables on the
front of the 1st and 2nd sections
4. Using an appropriate lifting device, sling around the 4th
section boom and lift it up until weight is removed from
the bottom pads in the front of the 3rd, 2nd, and 1st
boom sections.
5. Loosen and remove the four capscrews holding the pad
doubler plate in between the 4th and 3rd sections.
Remove plate. Remove pads from this plate. Note all
pad locations and tag accordingly.
6. Loosen and remove the four capscrews holding the pad
doubler plate in between the 3rd and 2nd sections.
Remove plate. Remove pads from this plate. Note all
pad locations and tag accordingly.
7. Loosen and remove the four capscrews holding the pads
in between the 2nd and 1st sections. Remove pads.
Note all pad locations and tag accordingly.
8. Inspect pads for wear using previously mentioned
inspection criteria.
9. Install new pads with Teflon inserts on plates or boom
sections. Reassemble plates in boom in proper
locations.
CABLE TENSIONING
A boom assembly is considered properly timed when
telescoping sections extend equally relative to each other
and bottom out simultaneously at full retraction and do not
spring back out after retract pressure is returned to neutral.
Hydraulic extend cylinder construction will dictate which
extendable section will be the driver that the other extend
s e ct i o n s w i l l n e e d t o b e a d j u s t e d t o u t i l i z i n g c a b l e
adjustment.
A single stage cylinder will control first extendable section.
A dual stage cylinder will control second extendable section.
Timing sequence of cables will depend on number of
sections and the extend cylinder construction.
Design intent of the cable tensioning is to balance the
preload of extend and retract cables for each extendable
section. In addition, sequencing of the sections during
retraction requires retract cables of every section to be
indexed relative to each other.
Tensioning Setup Procedure
Tensioning must be done with the boom in the horizontal
position.
When tightening/loosening the first (adjustment) nuts on
cables, secure cable using the wrench flats at the front of the
cable ends to prevent cable twist. Excess twisting of cables
can cause premature failure.
Ensure boom is completely assembled and fully retracted.
1. Mark the front of each section with a chalk line as
indicated in Figure 4-7.
2. Extend and retract boom several times to establish
working state of cables.
REFERENCE ONLY