Dann Bartos
Target Electric Motors, Inc.
Vertical hollow-shaft motors present some unique reassembly challenges, one of which is setting end play. Here's a tip that applies to assembly of vertical hollow-shaft motors in the 320 to 440 frame drip-proof enclosures with grease lubricated lower guide bearings and oil-lubricated upper thrust bearings.
End play for these motors is set by adjusting the top lock nut that supports the motor shaft on the bearing carrier. Typical end play is 0.005-0.010" (0.127-0.254 mm). Instructions for making this end play adjustment may say to tighten the lock nut until all end play is removed, then monitor the shaft position with a dial indicator as the lock nut is loosened to achieve the proper end play. The motor must be vertical to make this adjustment. With only a slight shaft extension on hollow shaft motors, there is no convenient way to secure the shaft while turning the lock nut (see Figure 1). Some technicians have been known to use a hammer and bar (or a chisel) to tap the lock nut around, resulting in ugly damage to the lock nut. Tapping on a spanner wrench will help prevent damage to the lock nut, but that's clumsy since the shaft turns with every tap.
Here is a tip to eliminate the difficulty in adjusting the lock nut for these size motors.
I've been doing this the last few years to make assembly easier and to avoid distorting the nut (see Figure 2). When I have the bearing carrier and bearing in place on the top and am ready to adjust the nut, I lift the motor off the floor and put a small end bell under the motor and let the motor back down so that the shaft extension rests on the small end bracket (see Figure 3). This forces the rotor upward to the maximum amount (until the lower bearing hits the retainer).
While the weight is still resting on the small end bracket, I take my rubber mallet and drive the bearing carrier down on the top end, and then the nut can be adjusted by hand. Then, while monitoring the shaft position with a dial indicator, I take the small end bracket out of the way and set the motor back down on the floor. Usually, the nut is set in about the place I want it; no hammer and chisel are required. This makes gravity work for me instead of against me.
This innovative method makes adjusting the end play easier on these 320 to 440 frame hollow-shaft motors.
For larger frame hollow-shaft motors, caution should be used to avoid overloading the lower guide bearing by resting the weight of the stator and housings on that lower bearing. The EASA Mechanical Repair Fundamentals of Electric Motors, 2nd Edition manual provides several additional methods that work well on larger hollow-shaft motors.
ANSI/EASA AR100
More information on this topic can be found in ANSI/EASA AR100- Section 2: Mechanical repair
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