Bearing replacement and clean up of electric motors

[Bobby Robbinett]

So I am rebuilding a 1990’s 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?

[Carl Beckett]

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

[Matt Day]

Carl - there are no capacitors, it’s 3 phase.

I’d take it apart and make sure it’s 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 isn’t cracking or anything, and that’s about it really. Not much to 3 phase motors as you said.

[Mike Kees]

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.

[Bill Dufour]

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

[Jerry Bruette]

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.

[Frank Pratt]

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.

[Jerry Bruette]

At least there's an easy fix for that.

You still feel stupid until you figure out what you did wrong.

[Bill Dufour]

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

[Mike Henderson]

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

[Bobby Robbinett]

Thanks for all of the replies fellows!

[Bobby Robbinett]

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?

[Bobby Robbinett]

Carl - there are no capacitors, it’s 3 phase.

I’d take it apart and make sure it’s 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 isn’t cracking or anything, and that’s 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.

[Carl Beckett]

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.

[Jerry Bruette]

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.