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Thread: Bearing replacement and clean up of electric motors

  1. #1

    Bearing replacement and clean up of electric motors

    So I am rebuilding a 1990ís era machine that has 4 electric motors. I want to break down the motors, clean them and install new bearings. The motors are 3 phase so not much to them. The machine did get rained on tor several hours transporting it back to my shop. So it has a lot of rust. This is my first time reworking an electric motor. I have rebuilt many machines but never did the motors myself. I am fully competent wrt bearing replacement. My question to you guys is, what else should I look for or do to the motors while I have them apart? They all run fine so the windings seem ok. That is something I know would be best done by an electric motor shop. Assuming the windings are good, what else do you guys suggest I do while replacing the bearings?

  2. #2
    Join Date
    May 2008
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    Clean out dust and debris from the windings. Blow it out with air (I have washed before but recommend simple air blow out). Look for any loose 'bindings' and get some cord and rebind. Look for any damaged insulation that could arc to ground. I also give the end windings a fresh coat of motor winding lacquer.

    If it has a start cap, there may be a cutout switch that runs on centrifugal momentum (single phase do, I do not know about 3 phase). Clean inspect and relube.

    And sometimes I put a new capacitor, for good measure.

    Many youtube videos on it - look there for some tips.

    Unless windings degrade should run for many many more years with new bearings

  3. #3
    Join Date
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    Carl - there are no capacitors, itís 3 phase.

    Iíd take it apart and make sure itís completely dry. Clean out all the old sawdust and crud that builds up around the windings (air compressor and/or old toothbrush). Replace the bearings, check the wiring isnít cracking or anything, and thatís about it really. Not much to 3 phase motors as you said.

  4. #4
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    I have a phase converter at my shop (Big three phase motor) that I purchased used. After it was all hooked up and running I noticed one day that the bearings made quite a bit of noise on wind down. I switched off the breaker powering it and just pulled it apart. On mine the cleanup part was blow out the mouse terds and then I used my shop vac to suck anything loose up. Went to town and picked up new bearings and put it back together. I still think that three phase is magic.

  5. #5
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    Three phase is dead easy to do the bearings. No switches no centrifugal switches no caps. A quality motor will have bearing size listed on the nameplate. Use sealed bearings for dust. Easy to pull apart since both ends are free of wires.
    I agree dust it off inside and add some extra varnish if it looks like it may help stop vibration of the windings.
    Bill D

  6. #6
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    Be sure to mark your end bells so they go back on in the same position, and make sure you don't swap ends with the end bells and the rotor or your motor will run backwards DAMHIKT.
    Confidence: The feeling you experience before you fully understand the situation

  7. #7
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    Quote Originally Posted by Jerry Bruette View Post
    Be sure to mark your end bells so they go back on in the same position, and make sure you don't swap ends with the end bells and the rotor or your motor will run backwards DAMHIKT.
    At least there's an easy fix for that.

  8. #8
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    Quote Originally Posted by Frank Pratt View Post
    At least there's an easy fix for that.
    You still feel stupid until you figure out what you did wrong.
    Confidence: The feeling you experience before you fully understand the situation

  9. #9
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    For small fan motors that are not reversible you can remove the fixed windings and flip it around to reverse the motor.
    Bill D

  10. #10
    Quote Originally Posted by Bill Dufour View Post
    For small fan motors that are not reversible you can remove the fixed windings and flip it around to reverse the motor.
    Bill D
    For a 3-phase motor. you just reverse two of the three wires to reverse the motor. But I assume you were referring to a single phase motor.

    Mike
    Go into the world and do well. But more importantly, go into the world and do good.

  11. #11
    Thanks for all of the replies fellows!

  12. #12
    Quote Originally Posted by Bill Dufour View Post
    Three phase is dead easy to do the bearings. No switches no centrifugal switches no caps. A quality motor will have bearing size listed on the nameplate. Use sealed bearings for dust. Easy to pull apart since both ends are free of wires.
    I agree dust it off inside and add some extra varnish if it looks like it may help stop vibration of the windings.
    Bill D
    Bill do I have to disconnect any wire or the power cord to pull the rotor out?

  13. #13
    Quote Originally Posted by Matt Day View Post
    Carl - there are no capacitors, itís 3 phase.

    Iíd take it apart and make sure itís completely dry. Clean out all the old sawdust and crud that builds up around the windings (air compressor and/or old toothbrush). Replace the bearings, check the wiring isnít cracking or anything, and thatís about it really. Not much to 3 phase motors as you said.
    Matt, any suggestions on how to clean up the shaft? I pulled the pulleys off the other day and the shafts look a little rough. I figure that I could just take some degreaser and white vinegar/baking soda to it with a Scotch Bright pad and give it a good cleaning, just want to get sone more opinions.

  14. #14
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    Does it look like the bearing could have been spinning on the shaft? The inner race of the bearing needs to be tight on the shaft - if the bearing got sluggish sometimes the race spins on the shaft and becomes a problem.

  15. #15
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    Quote Originally Posted by Bobby Robbinett View Post
    Bill do I have to disconnect any wire or the power cord to pull the rotor out?
    Nope. There's no wires connected to the rotor. One of the bearings will be a "held" bearing, the one nearest the output shaft. Might be held with a bolt on keeper or possibly a snap ring in the end bell.
    Confidence: The feeling you experience before you fully understand the situation

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