Motor Rebuild - Questions

[Allan Speers]

I've decided to rebuild all of my older motors, just because.
They are typical 1 - 5 HP TEFC's, both 1 phase & 3 phase.

I have 4 questions:

1: What brand of bearing do you think is "the best?" I'm thinking NSK, unless there's a better option.

2: Where's a good place to buy such bearings, for a variety of older motors?
--------------------

3: When mounting the bearing on the shaft, do you recommend just a "dry" fit, as in using a little WD40 which will then evaporate off. Or do you recommend using some kind of compound, such as Loctite 641 bearing retainer?

4: This concerns the bearing beds. I've seen videos that recommend using a little molybdenum grease. Oddly, I've seen other videos that recommend using Loctite 609 bearing retainer! These two methods could not be further apart.
And some guys just lay them in there dry, after cleaning the beds with brake fluid.

What's the general consensus around here?

[Bill Dufour]

If the bearing fits are not worn no need for anything. Grease or oil will dry up and make removal harder. Do not do it unless you expect the internals to get badly rusted. The bearing retainer compounds are only used if the bore or shaft is badly worn so the bearing is no longer a good fit and you are worried it will spin and damage the motor.

You also need to remember that only one bearing, normaly the out put end, is locked into the bore or onto the shaft. The other bearing has to be a tight slip fit on the shaft or into the bore to allow for the motor shaft to expand as it heats up. If you glue both in place the bearings will quickly wear out from the thrust load.
Bil lD.

[Ron Selzer]

dry fit
3 phase is easy
1 phase the start equipment I am still struggling with getting back together without damage and working good
bearing supply house or ebay or Amazon, small bearings are fairly cheap

[Allan Speers]

If the bearing fits are not worn no need for anything. Grease or oil will dry up and make removal harder. Do not do it unless you expect the internals to get badly rusted. The bearing retainer compounds are only used if the bore or shaft is badly worn so the bearing is no longer a good fit and you are worried it will spin and damage the motor.

You also need to remember that only one bearing, normaly the out put end, is locked into the bore or onto the shaft. The other bearing has to be a tight slip fit on the shaft or into the bore to allow for the motor shaft to expand as it heats up. If you glue both in place the bearings will quickly wear out from the thrust load.
Bil lD.

Thanks, Bill

re the back end: I thought the idea was to leave a little room there and use a wave washer in the gap, which then compresses as the motor heats up.
I've never actually been inside a motor, but I've seen this is demo vids and some motor diagrams.

No?

[Richard Coers]

I guess you already have a hydraulic press, pullers and an array of pipe and mandrels to press bearings off and on? Never been inside a motor, but I've stayed at a Hoiliday Inn, right? LOL I was raised on a farm, "If it ain't broke......" is part of my credo.

[Bill Dufour]

Thanks, Bill

re the back end: I thought the idea was to leave a little room there and use a wave washer in the gap, which then compresses as the motor heats up.
I've never actually been inside a motor, but I've seen this is demo vids and some motor diagrams.

No?


On my Unisaw the arbor blade end bearing is locked in with a screw in bushing.. The shaft is thread with. alock nut sop it stays in place inside that bearing. On the other end that bearing is also held onto the shaft with a nut but the outer race is free to move in and out. If the bearing froze it would soon wallow out the bore in the arbor casting and make the saw scrap unless it could be rebored in a milling machine somehow.
I have also seen the wave washers or bellville washers used to keep the bearing from floating too much.
My old neighbor told me of a big generator that the bearing were too tight to turn under load so he had guys up on ladders loosen the bearing hold down bolts until it magnetically centered itself and started to run. Then they tightened them down in place.
Bil lD.

[Bill Dufour]

PVC pipe and couplers are good enough to make pushers to seat bearings. I split it length wise and make it smaller with a few hose clamps when needed. I aslo grind the inside of the old bearing a little so it is a easy slip fit, same with the outer race. Then I usually take it apart to use to install the new bearing. removing the old bearing usually destroys it anyway.
Bil lD.

[Bradley Gray]

"If it ain't broke......" +1 on this.

[jared herbert]

A person can cause a lot of damage trying to fix something that doesn’t need to be fixed. Don’t ask me how I know this

[Bill Bukovec]

I ordered bearings for my lathe last year. They were only $20.00. They charged me another $20.00 for shipping. I had placed the order over the phone, so I didn't ask for a total, including shipping.

[David Kumm]

Most bearing manufacturers will make a little higher quality ABEC 3 bearing. Some call it an electric motor bearing, some use a different name. SKF Explorer and natchi Quest are two i know of. NSK, SKF, Natchi, are pretty similar in quality. A standard. motor bearing will usually have a C3 clearance to give the balls a little more room due to the bearing running in a warm environment. The ABEC 3 bearings will usually be standard clearance. SKF JEM bearings are C3. If the motor bearing also drives a spindle that needs low run out, like a direct drive unit or in a shaper, I always go go higher precision and tighter clearance. In a standard duty pulley application any decent bearing is fine. Odd brand or really cheap bearings are to be avoided but no need for Barden, FAG, Fafnir or other top end bearings. Dave

PS, if you don't have a press, use a small light bulb and heat the inner race and the bearing will slip on. No need for any Lock. tight unless the shaft is screwed up.

[Allan Speers]

Thanks, guys.

So is the consensus on the bearing beds to just dry fit?

[Frank Pratt]

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

[Allan Speers]

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

Esp when some motors are 30+ years old.



So?

[Jerry Bruette]

As long as the end bells of your motors are in good shape you don't need anything in them. You could use a little oil so the bearing slips in easier but there's no need for grease or any retainer.

If the bearings in the motors are 30 years old, why not replace them with the same brand bearing?

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.

Make sure to mark your end bells, motor casing and shaft with punch marks so you put it all back together in the proper order and place. I've seen motors that weren't marked put together backwards and when they were wired up would rotate in the wrong direction. Don't confuse Belleville washers with the wavy washers on the inboard bearings, they're two different creatures with different purposes.

Please don't drive yourself insane picking a bearing brand. I've taken apart brand new Baldor Gold motors that had two different brand bearings installed. NSK, Natchi, SKF, Fafnir, FAG are all very good brand name bearings that will all do what you want. I'd stay away from stuff from the local automotive parts store. Don't get all knotted up about the country of manufacture either. All of the above manufacturers have facilities around the world that make bearings to exacting specifications so your motor will run smoothly.

[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:D........Regards, Rod

[Michael A. Tyree]

I'll come at this from my own perspective- Why do this unless "a motor", has "a bad bearing"? :confused:
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"? :confused:
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!" :p

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:D........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.