Bench Grinder Motor Troubleshooting
 

So my old bench grinder crapped out on me. It would only hum when i went to turn it on. I think the bearings need replaced, but upon teardown and inspection I also found this:

This thin round ring which has been eroded. Does anyone know what that part is called? Is it susposed to be a continuous circle? Just thought id throw the question out here before I hit the motor shop next week.

Re: Bench Grinder Motor Troubleshooting
 

It looks like a thrust washer used to control end play. Like in a auto trans, though I don’t know if motors use them to control armature end play.

Re: Bench Grinder Motor Troubleshooting
 

Did you check capacitor?...or could be the start circuit....careful though,,the capacitor can store power.....if you have no electrical background it's best left to the experts..
not sure about worn part....

Re: Bench Grinder Motor Troubleshooting
 

If you could hand spin it, then it probably wasn't the bearings. More likely it was the start up gizmo. Some use a capacitor, others have a centrifugal operated switch that runs a 2nd coil to start the thing spinning. Bad switch = no spin. Could be what the worn thing did.

Re: Bench Grinder Motor Troubleshooting
 

Thanks for all the replies! I didnt realize this section got so much traffic.

I never considered that part to be a thrust washer Doug. I just thought it had something to do with the electrical process as it was very thin and there was corresponding arc marks on the shaft going through it. IDK.

I wondered if the capacitor could be the original culprit in all of this. I have limited experience here though. The bearings do not roll smooth though. With the wheels off the shaft, it is hard to turn by hand and there are a few tight spots. Perhaps the additional resistance from worn bearings or other internal parts burned up the start capacitor?

I admit I am no electrician/motor guy. I just thought I would have a look and see if it was something easily/cheaply fixed and perhaps learn something along the way. Thanks for all the info guys!!

Re: Bench Grinder Motor Troubleshooting
 

Unless it's a expensive name brand grinder I'd probably junk it and get a new one...motor repair could easily cost more than its worth...especially with your other issues...
I've had my baldor for about 30yrs...and it was old when i got it....and if it ever goes I'm getting a vertical belt sander

Re: Bench Grinder Motor Troubleshooting
 

Seeing the 2 wires connected which appear to be grounds i'd say when that wore all the way through you lost that upper ground and it wont run for that reason. Worn out bearings allowed the rotor to make contact with it. You can more than likely rebuild it, or replace it. Take it to a shop and see what they say. If the bearings don't spin over freely its definitely time for a rebuild.

Re: Bench Grinder Motor Troubleshooting
 

It was given to me approx. 5 years ago when it was presumed to be on its last legs. Id say I got my moneys worth. Lol! Its an older import, but still built way better than a HF unit. A vertical belt sander would be very cool!

Thanks for the reply! My initial assessment of the bearings I believe was inaccurate. Yes, they did not spin freely. After thoroughly cleaning them and repacking they now turn easy. Perhaps some grit got in there? So after seeing this I wire brushed and blew off the rotor? and stator? and put it all back together. Success! It will now run if I give it a push start. I would still like to fix this issue but at least I feel I accomplished something. Prior to teardown it would only hum and didnt respond to me rotating it when I tried to start it.

However,
In my haste to have a working grinder, read impatience, I purchased its brother off of CL. Similar model, same era circa 1980, but equipped with a wire wheel and a fresh stone. So now Ive got 2 grinders. :lol: