Motor Rebuild - Questions

[Allan Speers]

Better yet, if you have a few spare hours you could go the the SKF web sight and do some research on how to mount and install bearings. They'll show you what to look for in your end bells and on the journals of the shafts. They'll explain what's good and what's bad along with the proper nomenclature for parts and conditions and what to do to correct abnormal conditions.

Nice.

Thanks!

[Andrew Seemann]

And yet, I could really use an answer, since I firmly believe in preventative maintenance.

Esp when some motors are 30+ years old.



So?

So I am into preventative maintenance myself, probably to a fault, but even I don't go tearing into motors to replace things that show no sign of degradation. If a motor needs work, it will tell you

I have motors in my shop that are 30, 40, and 50 years old that are just fine. Replacing anything on them would just waste a perfectly good part and risk damaging the motor in the process.

[Charles Taylor]

Ball bearing replacement is normal maintenance after 20-30 years. The grease dries out and becomes waxy, and/or collects dust and grime. Bearings can fail and do damage without giving you obvious signals, so I usually replace the bearings in a new-to-me motor of at least that age.

Pullers, arbor presses, lengths of pipe and tubing, etc. are definitely your friends. Often you can get a bearing on a motor shaft by heating the bearing atop an incandescent light bulb for a few minutes. Wear gloves, obviously, and the expansion from heating may allow it to slip on easily. Be ready to back it up with a press or a tap from a hammer and your collection of pipe and tubing. Always make sure to apply force to the bearing race that is being fitted to the other part--the inner race when pressing onto a shaft, or the outer race if fitting into an end bell, etc.

No Loctite without an obvious need. Whoever replaces the bearings in another 30 years will thank you.

[Eric Danstrom]

I've just finished rebuilding 3 Shopsmith headstock with motor (7 bearings and two belts), 2 jointers, a 6x48 belt sander, 2 handsaws and a jig saw. I have a pile of dead shielded bearings that I replaced with sealed. I did buy a Harbor Freight 12 ton press and puller kit. Money well spent as nothing was damaged and all is running well now albeit much quieter. If I am still woodworking in 30 years that will be quite an achievement....

Single phase motors have either a starting relay or centrifugal switch. Neither is hard to deal with it just takes a little extra effort. I take lots of pictures as I pull things apart, never can take too many digital pictures.

[Rod Sheridan]

PM is a good idea.

Along with bearings change the motor capacitors, and the centrifugal switch contact assembly.

I also measure the insulation resistance of the motor.

Then ignore it for another 30 years........Regards, Rod

[Michael A. Tyree]

I'll come at this from my own perspective- Why do this unless "a motor", has "a bad bearing"?
Every motor I've stopped using and replaced was not a bearing issue at all! It was electrical and unless you like the idea of hours & hours of rewinding a motor yourself, ebay/CL motors when ones needed make more sense to me than bearings unless the motors got worn out bearings.
My 8" jointer uses a 1hp motor I inherited from my grandfather. It's 110v and probably weights a 1/2 ton (well lets agree it's really heavy) and spins up fast and strong. I've not seen it in over 30 years but no doubt it has bronze bearings.

[Jerry Bruette]

I'll come at this from my own perspective- Why do this unless "a motor", has "a bad bearing"?
Every motor I've stopped using and replaced was not a bearing issue at all! It was electrical and unless you like the idea of hours & hours of rewinding a motor yourself, ebay/CL motors when ones needed make more sense to me than bearings unless the motors got worn out bearings.
My 8" jointer uses a 1hp motor I inherited from my grandfather. It's 110v and probably weights a 1/2 ton (well lets agree it's really heavy) and spins up fast and strong. I've not seen it in over 30 years but no doubt it has bronze bearings.

How do you determine if a bearing is bad? Do you wait for it to start to squeal or listen for it to start rumbling, or maybe you check the radial runout of the shaft? If you're doing any of these you're waiting too long. By the time you hear something wrong with a bearing it's not going bad, it already went bad. I've seen more motors need repair because of bearing failure than electrical failure. I've seen end bells turned to junk because of a bearing spinning in them, I've seen shafts ruined or cut off from bearings seizing on them. All that is called reactive maintenance Allan wants to do some proactive maintenance. Let him have at it. He'll probably learn a few new things and have a better understanding of how motors work, gain some personal confidence and not have to buy a new motor because he waited until something major goes wrong that he can't have repaired without spending alot more than the cost of a few bearings.

[David Kumm]

I think the numbers are that over half of motor failures are bearing related. That is especially true now that wire insulation is so good that smaller frame motors have become common. The bearings operate in a higher temp environment compared to the old large cast iron motors. Dave

[Jacob Reverb]

Or the consensus is if it ain't broke, don't fix it

If it ain't fixed, don't break it!

In the same vein: "You can cut more OFF, but you can't cut MORON!"

In my limited experience, bearings are like the condensers in old car ignition distributors: If they don't fail within a few days, they just might outlive me (or at least the car). If you replace one that still seems to work fine, you go back to the "Will it fail within a few days?" gamble...plus there's always the added gamble of messing up something else while "fixing" something...like the fella who broke his TS arbor casting here recently. Do ya feel lucky?

YMMV

[Brian Holcombe]

I’ve yet to replace a 30 year old bearing in vein. In fact I’m starting to think it a good policy to replace all of the bearings from the get-go.

I did this recently on my Ulmia sliding table after one bearing died. All the rest were ‘good’ but not really.

My Maka was running when I got it, but it is a whole lot quieter now with new bearings and none of them were bad in an obvious way.

[Allan Speers]

PM is a good idea.

Along with bearings change the motor capacitors, and the centrifugal switch contact assembly.

I also measure the insulation resistance of the motor.

Then ignore it for another 30 years........Regards, Rod

Thanks, Rod.

I knew to change the caps, but didn't know about the centrifugal switch contact assembly.

- But how does one order this? How do you know what specific part you need?

[Rod Sheridan]

Hi, I normally order it from the motor manufacturer using the model and serial number......Rod

[Tom Bender]

Go ahead and take your motors apart, inspect and fix what is broken. Clean it because dust is bad for heat transfer, relube the bearings (replace if needed) and if there are brushes, replace them and clean up the commutator.