Motor bearings.

Daniel Macina

Daniel Macina

Well-Known Member
Ok. I can’t seem to catch a break with my grinder. Have bearings going out on the motor and wanted to see other then sealed is there anything I need to look for in bearings?

Thanks.
 
Why in the world would the bearings go out on motor? Is this an old motor? I replaced a bearing in my motor once and just got a sealed bearing of right size. Been working just fine.
 
KenH said:
Why in the world would the bearings go out on motor? Is this an old motor? I replaced a bearing in my motor once and just got a sealed bearing of right size. Been working just fine.
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It was used when I got it not 100% sure how old it was supposedly it didn’t have very many hours on it. sure sounds like a bad bearing. though it had been running fine the little I’ve got to use it on my grinder. Just happened to switch it on the other day for the heck of it and it sure sounds like a bearing. Might be something else though I’ll have to take a look
 
Capacitors are often the general culprit's of a motor. Bearings are more of a last thing!! If it comes to bearings on a electric motor it has been used and abused!! How does the motor run and sound with no load?? I would be more inclined to think you got a bearing going out on one of your wheels before the motor itself looses a bearing!! Pictures of your setup or a video with sound might help to locate the issue!!
 
I’ll add to the above: i’ve changed a ton of motor bearings in my career. Three things kill motor bearings:

1. environmental. Motors in hot, wet boiler rooms or outdoors in the elements that have an intermittent duty cycle. Even a sealed motor will build up condensation from getting hot/cold/hot/cold in a moist or humid environment and that moisture “breathes” through the bearings.

2. misalignment between the motor
shaft and the load. Think misaligned pulleys. A constant side load will eventually cause bearings to fail.

3. lack of lubricant. Sealed bearings have a lifespan. Grease is the same thing as oil, it’s just oil suspended in a soap. The oil eventually wicks out leaving the soap so that the bearings look greased but there is no actual lubricant left. The upside to sealed bearings is that you never have to grease them. The downside is you can never grease them. Like everything else, not all bearings are created equal. F.A.G. , NSK, or other top tier bearings last the life of the motor. Cheapie Chinese bearings are luck of the draw.
 
C Craft said:
Capacitors are often the general culprit's of a motor. Bearings are more of a last thing!! If it comes to bearings on a electric motor it has been used and abused!! How does the motor run and sound with no load?? I would be more inclined to think you got a bearing going out on one of your wheels before the motor itself looses a bearing!! Pictures of your setup or a video with sound might help to locate the issue!!
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There is no load on the motor at the moment. I had just re-wired a new VFD to replace the one I burnt out and turned it on and noticed the sound. Kind of reworking the grinder so there’s not even a wheel on it yet. I only really hear it at very low speed’s

I will try to figure out how to post a video tomorrow
 
With the motor shaft uncoupled, if you spin the motor shaft slowly by hand do you feel a rough spot in one part of the rotation? Sometimes you can put a screwdriver to the frame and listen as you rotate the shaft. Any clicking or dragging sound at the bearings is a dead giveaway. Usually if this is present the motor will have a “wah wah wah wah” sound that correlates to the speed it’s running.

Can you wiggle the shaft, or push and pull it in/out a tiny bit? If so, this is called “end play”.

Those two things indicate bad bearings.

If neither of those is present, but the motor is too hot to touch when running then you’ve got a winding going bad and the motor probably sounds like it’s oscillating or whining.

Again, if the motor has a fan on the shaft, make sure it isn’t broken or damaged because that will sure enough fool you if you don’t check it.
 
@John Wilson thank you I will check all that tomorrow. I wondered about the fan myself. The cover was slightly dented on the fan when I got it but never caused an issue. I wonder if I bent it a little bit when putting the motor back on and the fan is knocking against the cover? It does not seem to be getting warm at all although admittedly I haven’t had it running very long
 
Daniel Macina said:
It was used when I got it not 100% sure how old it was supposedly it didn’t have very many hours on it. sure sounds like a bad bearing. though it had been running fine the little I’ve got to use it on my grinder. Just happened to switch it on the other day for the heck of it and it sure sounds like a bearing. Might be something else though I’ll have to take a look
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I thought I had a bad bearing in mine, but I just needed to tighten the pulley. It sounded just like a bad bearing.
 
Kevin Zito said:
I thought I had a bad bearing in mine, but I just needed to tighten the pulley. It sounded just like a bad bearing.
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Yep. exactly. That’s why you always have to uncouple the motor because any imbalance along the drive train resonates at the motor. Even a loose v-belt fluttering will make the motor sound like it’s doing something funny.

All this stuff can have you chasing your tail very easily.
 
I have to ask when you guys say pulley are you talking about something inside the motor. My set up is direct drive with a VFD so no external pulley on my setup.
 
Ahhh. Ok. I should’ve said in my first post it’s on my GIB direct drive with VFD. I apologize for the misunderstanding.
 
With the VFD powered off, can you turn the shaft easily by hand? How does it feel? If you give it a quick hard turn with your hand, does the shaft keep spinning for at least a couple of revolutions? Often you can feel a bad bearing, whether there's a bit of a catch when you hit a flat spot, or if the motor shaft becomes hard to turn by hand. You may also feel excessive heat when running the motor for a few minutes. Does the shaft have any play/movement in and out, or up and down? That's a DEFINITE sign of a worn bearing. :D

Make sure it's not something simple like the fan blade rubbing on the shroud.
 
Since it's a direct drive it could well be the drive wheel that's loose causing a sound like bad bearing. I should have mentioned that before - it's happened to me.
 
I took my OBM wheels off to replace with aluminum wheels and haven’t put them on yet so there is absolutely nothing on the motor at the moment other then having the VFD wired up.
 
How low is the speed when you hear it?

Quite a few VFDs and motors do not run smoothly much below about 10 Hz. I’ve never heard an unloaded motor actually make a noise that could be mistaken for a dodgy bearing at low speed, but it seems plausible. If it’s quiet above 10 Hz, it could just be that.
 
Can’t remember off the top of my headWhat speed the motor is when the sound stops I would be shocked if it’s the VFD. At least for me it’s always been more kind of a surging of power at low speed not necessarily annoy what speed the motor is when the sound stops I would be shocked if it’s the VFD. At least for me it’s always been more kind of a surging of power at low speed not necessarily noise. Who knows I’m gonna check some stuff in a couple hours when I get home from work.
 
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