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Unisaw RI Bullet Motor

Modified on 2008/04/05 07:44 by Administrator Categorized as Restoration Topics


Bullet motors are specially shaped totally enclosed motors used on Unisaws from 1939 through (info needed). They came in both 1hp and 1.5HP single phase versions, and 1.5hp 3 phase industrial versions. The single phase motors are Repulsion Start - Induction Run type using a brush riding design.


The motor is made up of the following major components:
  1. "Bell" end caps
  2. Main housing, which contains the windings and wiring connections
  3. Armature
  4. Brush assembly (located in the round end of the motor)
  5. Bearings and springs


As motors go, these are relatively easy to work on, since there is no centrifugal switch mechanism to deal with. However, single phase bullets go for good money so it's worth taking it to a good shop if you're uncertain. Before you start, matchmark the end bells to the case so they go back in exactly the same position. This is important because it determines where the brushes are relative to the motor which is critical for starting direction. You'll find most motors are matchmarked already from previous service. A common method is to use a center punch to put one dot in each of the case and end bell at one end, and two dots at the other.

Start by removing the brush inspection covers on the round end. To open the motor, remove the 4 retaining rods and gently pry off the round end bell. On single phase motors, be careful when separating the armature from the brushes, and also be careful not to damage the windings of the rotor. Bearings in the early bullets are 87504 (extended inner race one side). They can be removed with a puller or press if you have it. Replacement bearings can be pressed on or driven with a piece of pipe just large enough to slip over the shaft. The pipe must not contact anything but the inner race of the bearing. The extended race points inward. There is also a spring in one end that applies pressure to the outer race of the bearing. Be sure to replace it in the same location and orientation that it came out of. While you're in there, it's a good idea to clean the gaps between the commutator bars, as carbon buildup in there can lead to a motor that won't start reliably. To reassemble, push the brushes back in their holders until they hold in the retracted position. If they don't slide smoothly, now is the time to gently pull them out and clean the brush holders. Do not remove or loosen the brush holder! Gently put the end bells back so the matchmarks line up. You may have to tap them home with a rubber mallet. Put the rods back through and tighten uniformly. Reach through the inspection ports and push each brush toward the center until the spring catches and holds it against the commutator. Replace the inspection covers and check that the shaft turns smoothly. If you've just done a bearing replacement and the shaft doesn't want to turn, give it a couple of pops with a rubber mallet to seat the bearings.

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