advice needed - electric motor bearing lubrication

On some older electric motors with sloppy bushings I have sucessfully used STP. Are the bearings ball, roller or just bushings?

I would take the motor apart and check each bearing. Most of the time I go to the bearing house and buy two new bearings. For $20-25 its seems worth it to me.

Gary Repesh

For a while

The industry standard for motor grease after Lithium based has been poly urea - Chevron was the most popular but had a problem in that it would crystalize when idle and make noise on start up until the crystals were reground. Didn't hurt anything but noise caused concerns. Since yours is now making the noise continuously I would guess there is some other problem. Keep in mind that if you can change bearings before catastrophic failure you may prevent damage to the windings.

Very possible - sometimes the nameplate will list the bearing designation but often the bearings are changed and may not be the same. Some companies will lube shielded bearings and the shield acts as a "meter" - at any rate, provisions for grease fittings are usually installed in case the customer wants to use them.

Technically, the bearings are lubricated with oil as the thickener only serves to retain the oil in grease but it's unlikely that they are lubricated with oil in the normal sense unless you see a reservoir mounted externally on the motor. Oil can easily flow into the windings and can serve to further dilute or wash out the grease and there is no way to confine it to the raceway of the bearing where it's needed.

The best and safest course of action would be to replace the bearings. Easiest would be to go back with shielded bearings and not worry about lubricating (almost everyone tends to over lube). For info, go to

, click on "Technical Support" then click on "Technical Supplements" then "Mounting & Dismounting Cylindrical Bore Bearings". If you go with a shielded bearing (wouldn't recommend sealed due to speed limitations) don't use the hot oil or hot plate method as you will flush out the grease. If you just don't want to change the bearings you can hit each with a shot of grease - best choice would be Exxon Poly Rex EM which is compatible with almost every other type of grease. If these are open bearings this may solve your problem for awhile. If they are shielded it may buy you a little time but understand that sealed and shielded bearings are designed to wear out before the grease does unless you have extenuating circumstances (heat, excessive contamination etc.) so you're still living on borrowed time. If you replace the bearings it's best to take the bearing to your local bearing distributor as the numbers on the bearing may not provide the complete description (they usually are the number for the individual component). Be sure the bearing has C/3 internal clearance or specifies EM (electric motor grade basically). Good luck.

On Thu, 22 Jan 2004 06:13:51 -0500, Nick Hull brought forth from the murky depths:

Nick, you need to know that STP is NOT a lubricant by itself so you don't tell anyone to use it by itself.

Back when I was a young, inexperienced punk attending automotive tech school (UTI, early 70's), I worked for a used car dealership (Ugh! Yeah, I know) in Phoenix. The shade tree who worked there was dipping freshly unwrapped main and rod bearing halves into straight STP "honey" during an engine overhaul. I warned the experienced mechanic that he would surely spin a bearing that way and he replied that he had been doing it that way for years.

I knew 2 things:

1) That STP was a decent additive but wasn't a lubricant. (Hmmm, update 1998: STP now actually contains oil!)

2) That putting anything semi-slippery behind a bearing would keep it from seating properly & possibly cause it to spin.

Sure enough, 3 days later, the guy who bought the car called from somewhere in Kansas with a blown engine. Yup, spun bearing. (See? Young punks aren't always wrong. ;)

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There is some info here:

You will need to fix word wrap on this one:

Thanks for the replies. They're ball bearings, undoubtedly modern electric motor bearings, just don't know about the shielded vs. sealed business.

Bob

Excellent post and that NTN site has much valuable info but there are two types of sealed bearings, contact and non-contact. The LLB (non-contact) can handle fairly high speeds, considerably higher than you are likely to encounter on a 60Hz AC motor. I just had occasion to use a pair of 6207LLB...'s which are considerably larger than you would likely find in a 7.5 hp electric motor and they have a limiting speed rating of 9800rpm.

Ted

See my post elsewhere in this thread. I wouldn't expect any problems from LLB sealed.

Ted

I don't put the STP behind bearings, just add it to the oil already on the bushings if the bushing is a really sloppy fit on the shaft and needs something with more viscosity to fill in the gap when running.

This is a guess, but I suspect that the motor is intended to be greased and has bearing with no shields or seals. At work there was a motor generator that had a motor of about that size. it was suppose to be greased at something like five year intervals if used 8 hr a day. Naturally the PM system had no provision for five year intervals and so even tho the motor was used about five hours a month, the PM required it to be greased annually. The excess grease came out as I remember from a hole under the shaft, about the same as the hole on top but 180 degrees away. Look and see if there is another hole with a screw in plug on each end of the motor. I just looked at a Century 7.5 motor and it is like I remember.

Dan

Thanks for the compliment and you are correct about the non-contact seals. I didn't mention those as some manufacturers don't make a non contact seal and he could run into problems using a contact seal. Unless he is operating in an extremely contaminated atmosphere he most likely wouldn't need sealed bearings and the higher cost that goes with them. What did you use the 6207's on?

NTN do make them and our local dealer had them in stock.

A pair are in the large pulley for a belt drive/speed reduction for the prop on a small homebuilt biplane my neighbour is building. I will post the details as soon as I get it all together, hopefully this weekend. Machining the six belt grooves on a ~9" pulley on my Smithy 3-in-1 definitely required thinking outside the box. :-)

Ted

Sounds like a fun project - is it a kit built, plans or his own design?

Plans. It's called a Ragwing.

Ted