Jump to content
I Forge Iron

Any way to save this motor?

Recommended Posts

Hi. I bought an old motor at a garage sale. It is a big heavy old-fashioned 1/3 HP induction motor. It worked at the sale, but just hummed when I plugged it in at home. I figured that I could fix it. How hard could it be anyway? First, I added some motor oil to the oiling ports with the spring loaded caps. This didn't help. So, I disassembled it and tried to see what was wrong. It was pretty obvious. The contacts and throwout ring for the centrifugal starter were heavily oxidized. After a thorough scraping with a junk screwdriver, I put the motor together. It would not spin once it was tightened up (a common problem with these old motors) so I loosened it up and tried to run it. It started up and ran smoothly, so I slowly tightened the case. It was running for a few minutes, when all of a sudden it seized up. I took it apart and found out that the shaft was frozen in the front bearing :( . I added a little more oil, but it did not help. Chucking the shaft in the vise, and turning the end bell did not help. It got even worse. This is one of those old fashioned motors with the bearing integrated in the cast iron bell, and there is noting to disassemble or press out. Is this old thing a lost cause? It is a lot of copper, iron and aluminum, so it is a shame to throw in the trash. It is a little heavy for one trash pickup, so it may have to be divided. That's OK; it is all apart anyway.

Is there any trick to salvage these old motors when they have this problem? It seems that old-fashioned is not necessarily good.

Link to comment
Share on other sites

It sounds like you should not have tightened the bolts while the motor was running. When I reassemble motors it is with a wrench to tighten the bolts and a hammer to get the bearings to settle in without binding. Turn the motor shaft slowly by hand and snug the bolts and lightly tap the ends to relieve any stresses on the bearings. Turning over by hand eliminates the possibility of seizing like you have experienced. By tightening those bolts while running you never knew the bearings were not happy until it was to late. Hopefully you can get it fixed and learn from the experience. Must be a way to get it apart and I think most old motors just had brass bushings not ball bearings.

Link to comment
Share on other sites

Hi. Thanks for the replies fellas. I will try to press the front of the shaft back through the bell. It looks like it is not worth fixing, though. I'll keep an eye out for another motor at the sales. Around the web, there were a lot of warnings about buying used motors. It is amazing how tricky these things are.

Link to comment
Share on other sites

Hi Biggundoctor. I am in Sunnyvale. Did you want me to save the junk motor parts for you? I don't feel too bad about throwing them in the trash, because they have a pretty sophisticated separation system here. Magnetic and all. They even have observers, and they catch much of the dodgy stuff that miscreants think they have gotten ride of in the trash.

Link to comment
Share on other sites

Thanks, biggundoctor, for the offer. I don't think it is worth saving. It has those old felt packed bearings, and I cannot even see where the front bushing is pressed in. It was really cheap at a garage sale. These things appear all the time. A new motor, maybe from Ebay or a local tool surpluser will be one of the next items on my shopping list.

As for machining, I have a striking partner who has mills and lathes. I bundle up my work, and when the pile is big enough, I give him a call :) Never been able to get into it myself. I guess that's why I like blacksmithing.

Link to comment
Share on other sites

  • 7 months later...

Don't put that aluminum and copper in the trash. If you don't want to take it to the scrapper, put it outside and see how long it takes someone else to grab it.

And if that doesn't work, put it in a cardboard box with birthday wrapping and ribbons and a card on it, and put it out by the street.
Link to comment
Share on other sites

  • 2 months later...

Hello fellow basher's

I am a bit surprised at two important details of procedure that have not yet been mentioned in the rescue attempts of plain bearing motors.

First- when you turn the shaft with one hand as you tighten with the other you will possibly find a point where there is the beginning of stiffness, as soon as you feel this and assuming you kept the tightness's of the bolts sort of even,rap the motor on the side (perpendicular) to the axis of the shaft.

Do this on the body of the motor for now, not the end bells.

Use the end-grain of a piece of two by four and a hammer, if needed.

First try a good blow on the side, as you turn the shaft.

Do the tightening in steps, I have found most motors of the size that yours is take about three steps.

(I have herein used the word bolts, it does not matter if the motor you have has bolts fixed or loose, within the stator, and therefore nuts are what you are tightening, or the motor has screws for each end bell, you may find the advise still applies, change the words to suit.)

During further tightening, binding may well occur again, then use the wood to "fix" the alignment again.

What is happening here, in the case of plain bearings, or journal bearings, their proper operation relies on a fairly thin and even coating of oil between the shaft and the bore of the bearing.
This oil film is self pressurizing once the motor is spinning, the thickness of the oil film is .001 of an inch, or so.

It is easy now to visualize the small misalignment that will cause this film to be squeezed out of existence on one or both ends of the motor.
This then causes metal to metal contact, and will therefore make a lot of drag, or even stop rotation altogether.

When one raps the side of the motor, it moves away from the force, and so the end bells remain in place.

Between the motor body and the end bells there is a certain freedom of radial play in almost every plain bearing motor I have ever seen, and these spaces or allowance is what lets us fine tune a motor.

Even a motor with seemingly tight end bells, I have found that I had to rap to "find" the sweet spot.

When you are finished, you may have the feeling that the motor could be even a bit more free in rotation, now try a rap on one end bell, or both.

Unless otherwise directed, use non-detergent 30 wt oil.

At the conclusion of this "massage" the space between the bearings and shaft have equalized at both ends at the same time.

You may to try this several times to get a good feel for the process.

We have been speaking of plain bearing motors, what about ball bearing motors?

These may have enough play between the body and end bells to benefit from this "massage" treatment.

The result will probably not be something one can feel as in a reduction of drag, but when you try you may feel and hear something that will guide you.

A well aligned motor with ball bearings will probably run noticeably quieter.

In regard to the bolts, how tight is enough? Use your best judgment, they do not need to be tightened more than any hardware of that diameter is, weather holding a motor together or almost any similar assembly.

Take your time, pretend you are small enough to be in these spaces in your mind's eye.

This viewpoint has helped me become a good toolmaker, and more.

Yours in building and rebuilding, Michael Visser

"Never throw away anything that has value."

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...