INSTRUCTIONS FOR INSPECTING LIFTING NUTS FOR THREAD WEAR IN DUFF NORTON
AIR MOTOR JACK MODELS 126RX, 144RX, 528RX, 536RX, 524RX, 228R, AND 326R
At the heart of every Duff Norton air motor jack is the
power thread mechanism—comprised of an externally
threaded lifting screw and an internally threaded
lifting nut. As the threads of the lifting nut make
sliding contact with the lifting screw, they begin to
wear. If the jack is operated long enough the thread
will wear to the point where it no longer has the
thickness required to support the jack load. When this
happens, the lifting nut will shear at the lifting screw
thread outside diameter, and the jack member will
collapse—bringing the load it was supporting crashing
down on the cribbing or blocking which should be
used in any jacking operation.
For this reason it is important to inspect the lifting nut
in your Duff Norton air motor jacks for wear at regular
intervals—after every 100 full extend and retract
cycles under full rated load when the jack is operated
with recommended lubrication in a clean environment.
Of course, the inspection interval should be modified
up or down based on the stroke, load, lubrication and
environment conditions existing during actual use.
The Duff Norton “Operating, Inspection and
Maintenance Instructions” manual covers inspection
of lifting nut threads for wear in great detail. The
procedure it describes is suitable for use mainly by
trained mechanics in authorized jack repair centers.
Duff Norton Air Motor Jack Co. has developed an
inspection procedure which is more readily used by
authorized jack repair centers. The procedure requires
that the lifting member be removed from the jack.
The lifting nut threads are then checked by measuring
them with a specially designed gage made from flat
sheet metal. The gage has teeth that enter the thread
spaces and indicate whether the threads are worn
beyond the allowable limit. A set of four gages (part #
X4829) for the various air motor jack models is
available.
Instructions for using the new gages for inspecting air
motor jack lifting nuts for thread wear are presented
below. These instructions involve only the inspection
of lifting nuts for thread wear. It is important that
other aspects of air jack operation, inspection and
maintenance as presented in the maintenance manual
be understood and followed for the continued safe
operation of jacks.
Duff Norton Air Motor Jack Co. has also developed a
video to show the inspection procedure.
Extra gage sets, gage use instructions, maintenance
manuals and the how-to video are available from Duff
Norton Air Motor Jack Co. at:
Duff Norton Air Motor Jack Co.
2111 4th Ave. N.
Billings, MT 59101
Phone: 406-252-4294
Fax: 406-252-4812
To disassemble the lifting member from the jack, to
inspect the lifting nut for power thread wear, to
replace worn out lifting nuts in lifting members, to
reassemble the lifting member into the jack and to test
the reassembled jack, refer to the exploded illustration
appropriate to the jack model and proceed per the
instructions below.
I. LIFTING MEMBER DISASSEMBLY FROM THE JACK
A. JACK MODELS 126RX, 144RX, 528RX,
536RX, AND 524RX
1. Disconnect the air supply from the
jack and position the jack upright.
2. Remove the bolts (Item 87 for 126RX,
144RX, & 524RX; Item 89 for 528RX &
536RX), the lockwashers (Item 88 for
126RX, 144RX, & 524RX; Item 90 for
528RX & 536RX), and the handle bracket
assembly (Items 81-86 & 89 for 126RX,
144RX, & 524RX; Items 83-88 & 91 for
528RX & 536RX) from the jack.
3. Remove the screws (Item 90 for 126RX
& 144RX; Item 92 for 528RX & 536RX;
Item 97 for 524RX), the lockwashers (Item
91 for 126RX & 144RX; Item 93 for 528RX
& 536RX; Item 98 for 524RX), and the
throttle lever guard (Item 92 for 126RX &
144RX; Item 94 for 528RX & 536RX; Item
99 for 524RX) from the jack.
4. Loosen the check nut (Item 98 for 126RX
& 144RX; Item 100 for 528RX & 536RX;
Item 91 for 524RX) on the control rod (Item
99 for 126RX & 144RX; Item 101 for
528RX & 536RX; Item 90 for 524RX).
5. Remove the check nut (Item 76 for
126RX & 144RX; Item 78 for 528RX,
536RX & 524RX)
