Motor bearing issues...

A

AndrewC

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Nov 14, 2017
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My brand-new 1hp 3ph grinder motor is making noises ("bump-bump-bump" - not belt seam, definitely in the motor) - and it's the 2nd motor to do that; in fact, it's the warranty replacement for the 1st. The tech support guy at the supplier said something about me putting a ("lateral"/"side"?) load on it - i.e. the belt tension on the drive wheel pulling the shaft sideways, vs. the motor just turning something on the same axis. That that'd possibly damage the bearings, hence the thump-thump-thump. The reason they replaced the 1st one under warranty was that they didn't actually say the motor wasn't rated for a (whatever) load - but I got the sense that might get updated. >;-)

ANYhow: I now have 2 motors - otherwise pretty nice, and one effectively free! - with (I think!) bad bearings. Should I replace the bad bearings with better ones (maybe roller/needle instead of ball?) that can handle a side-load. Has anyone had similar experiences, or have any good knowledge as to where to go from here? (Please: do NOT respond with "you should've bought a better motor, go with Baldor/Leeson, etc." scoldings - advice is about the future, not the past. :-) MUCH appreciated!
 
The tech support guy at the supplier said something about me putting a ("lateral"/"side"?) load on it - i.e. the belt tension on the drive wheel pulling the shaft sideways and damage the bearings ?????????????????????????
Well I read many nonsense on internet , but this is ......................:thumbsdown::thumbsdown:
 
You are pretty much stuck with whatever bearing type its designed for.
For example, if you could get tapered roller bearing of the right size and sealed. Of typical motor design, there is no method to set their preload. Its not gonna work...

If its a cheapo motor implied as you warned about not saying ”should of bought brand XYZ” might suggest its built with cheap bearings too.
Just replace with good quality bearings (what are remarkably inexpensive btw) & get it back to work.
 
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Is there play in the shaft? Or is it just making noise? Does it now click with no load on the shaft? Does it spin easily without power?
I agree with Lieblad, you're not going to be able to change much as far as bearing types are concerned, though you might find a higher quality in the same size, assuming it's not some real oddball size. You don't necessarily want to put 500lbs of side load on a smallish motor like that, but the tensions your average belt grinder is going to see should be relatively negligible on a decent set of bearings.
 
First thing I would do is take the belt off and compare the sound. If it is still making the sound, its the motor, if it is gone, look elsewhere. The few pounds of spring tension from the tensioner should not destroy any bearings.
 
You have not mentioned which grinder you have or which motor. More details would be helpful.

Most industrial motors are designed/built to be universal: everything standardized for each frame size, with feet, flange-mount- or face-mount-endcasings fitted as needed.

The only way I could see the side-load being an issue is with a single-purpose flange- or face-mount motor being used for a purpose other than that for which it was designed. Face- and flange-mount applications usually locate the motor inline with the load. An hydraulic pump application with the motor shaft vertical might reasonably be expected to see zero radial load and have its bearings specified on that basis. Something like a waste-disposal motor could be similar? Using it on a belt grinder intended for a general-purpose motor with face- or flange-mount casing would subject it to radial loads for which it was not designed. Purpose-designed motors tend to be used only when the production run is long enough for the small saving-per-unit to offset the cost of the production setup.

There would be a pretty good chance that such a motor would work fine on a disk grinder, where the only radial load is the weight of the motor rotor and the disk. Make the disk horizontal and even that radial load is removed.
 
Stacy E. Apelt - Bladesmith said:
First thing I would do is take the belt off and compare the sound. If it is still making the sound, its the motor, if it is gone, look elsewhere. The few pounds of spring tension from the tensioner should not destroy any bearings.
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I would add to try to take of drive wheel and to compare sound .Two motor with same problem ? I don t know the size of drive wheel , but if they have no good balance they can ruin bearing VERY fast and unbalanced wheel produce strange sound too.

AndrewC said:
My brand-new 1hp 3ph grinder motor is making noises ("bump-bump-bump" - not belt seam, definitely in the motor) - and it's the 2nd motor to do that; in fact, it's the warranty replacement for the 1st.
Click to expand...
 
Andrew
Since you have the same problem on both motors, and without hearing the noise or knowing the exact circumstances, I'm going to propose an alternate source of the noise. When sycronous motors slip out of phase they make a noise refered to as "cogging". This can occur because of excess load and I'm guessing undervoltage could cause this also.
I suggest you check the voltages appled to the motor to insure they are the same as the motor is set up for and they are all equal. The problem might be in your VFD or the wiring.
Jim A.
 
Is this motor run off a VFD? I had to adjust some settings in the VFD to lower my motor whine and to eliminate a vibration I had..
 
PROBLEM SOLVED. (Answer, and helpful reminder, below.) 1st off, though - excellent suggestions all, and thank you! I actually thought it might be the VFD - I ran into some thoughts on line that they can set up a resonance/feedback loop that - besides the whining thing some folks get - can make a mechanical noise from the motor. Spent some time with the KBAC mfg's excellent tech support and eliminated that right away when I noticed it still "bumped" every revolution - turning it manually with the VFD unplugged. I also tore down the original motor to see if there was bearing damage - couldn't find any noticeable play. Finally, though, I was fiddling with the drive wheel and feeling a little play (the "bump") when I jiggled it. But noticed when I moved the wheel a little on the keyed shaft while doing this - the play WENT AWAY. And sure enough when I turned the motor on, with the belt - no more bump.

SO: the problem was: when I'd remounted the original motor on the bench, I had removed and re-installed the 4" drive wheel. The key was a bit sticky and slightly jammed in the keyway so I'd gently sanded it a bit. Things worked fine for a few days, but then the bumping started; I replaced the motor; things were fine; then the bumping started again. Apparently the key was JUST loose enough that sometimes it 'jammed' just right to hold the wheel true and/or tightly; other times not. Then my Homer Simpson "Doh!" forehead-slap moment: "oh yeah - there's a set-screw in the hole over the key. Fergot 'bout that...."

The Prime Directive of Troubleshooting is: "What Changed (right before the problem started)?" The answer in this case was that I'd removed and re-installed the drive wheel, sanding the key a bit in the process. Therefore, I should've looked at the wheel and key first - not the motor.

Filed under Lessons (re-)Learned; Case Closed. (Cue sound of gavel; theme music from Law & Order....)
 
Don't you just love it when you can actually find and ID the problem rather than it just going away? I had a VERY similar thing with similar sound once when the drive wheel got loose. Thinking bad bearing (as you did), once I checked the drive wheel and tightened setscrew, problem went away. Congrats to you.
 
My brother! (fist bump). :-) And yes, it's so satisfying - even if it's a bit embarrassing when you have that satori moment of "ohmigawd, it was THAT?!?!?" - to have it solved and known.

It's amazing, and again deeply satisfying, how these experiences build into a body of knowledge that isn't just an "If A then do B" kind of thing -- it's an approach to not just fixing things, but designing them going forward. From "OK, what happened?", to "OK, what could happen wrong, and how do I design that out?".

I just watched a YouTube vid of a genius young guy who built his own (amazing) 2x72 and then quite a lot more accessories for it. He made a T-shirt that says something like "If you can't make it perfect - at least make it adjustable.". I'm still grinning.
 
Spalted said:
Now that you know it was your doing and not a bad motor do you keep both or do the right thing and send one back ?
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Good question (and good moral conundrum) - turns out the mfg. doesn't want it back. They had me take the nameplate off and send it back to them as a proof of 'return', because packing it back up and shipping cost back to them would've been more than the (non-resellable) motor was worth. Even the 2nd one, with a nameplate, would be far more cost of both shipping and verifying its condition vs. what it could be sold for as a used or reconditioned motor. So - no, they don't want it - either of them - back. :-)
 
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