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Motor Ball Bearing Lubrication

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Dale7905

Electrical
Dec 9, 2006
3
Hi all,

I have an older 1/2 HP, single phase, capacitor start motor with ball bearings on the rotor shaft. I don't know how old the motor is but when inspecting the bearings, they seem a bit shy of grease/lubrication.

I was wondering if there are any guidelines for adding/changing lubricant (grease/oil) to the motor bearings that anyone cares to share? I know in the automotive industry when lubricating the wheel bearings, it is strongly advised that all the old lubricant be thoroughly cleaned from the bearing so that the new lubricant doesn't cause any adverse chemical reaction with the old lubricant. I was wondering if the same type of procedure should be done with the bearings in fractional HP motors. And if so, what is a good technique for cleaning the old lubricant from the bearings.

Thanks for any comments.

Newbie Dale 7905
 
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So this bugger doesn't have sealed bearings?

Often on motors that small you don't bother with bearing maintenance you just replace them occasionally or when they fail.

You always want to clean out the old grease for the reason stated and because metal fragments (dust) starts loading up the existing grease with predictable results.

Stay tuned: Some actual motor guys will be along shortly..

Keith Cress
Flamin Systems, Inc.-
 
ItSmoked is right.......I wouldnt bother cleaning and repacking the bearings on a 1/2hp motor. They wont be big and costly so I would just replace them with new but this time sealed items. If you do choose to go down the re-pack road just clean them out with any propriety de-greasing solution, dry them off throughly and repack with fresh general purpose grease. Dont use too much, just enough to fill the race flush with the sides. Otherwise it can overflow and attract dirt or find its way onto the winding where it can shorten the life of the insulation. Bear in mind though if they have been running without adequate lubrication the damage will have already been done.
 
One procedure is to remove the drain plug and then pump in grease until fresh grease is issueing from the drain hole. Then leave the drain open and run the motor for an hour or so and let the excess grease drain. Then replace the drain plug and forget it for a few years.
More small motor ball bearings have failed from over greasing than from lack of grease.
Be sure that the bearings are greasable. If the bearings have been replaced with sealed bearings at some time, they may be damaged if you attempt to grease them.
respectfully
 
If you do decide to clean them out and dry them, do not hold them on your finger and spin them with compressed air. At this point they are unlubricated and you can reach some pretty high RPM's, resulting in wear, which you were trying to avoid, or damage. I have seen auto wheel bearings throw one or more rollers out of the cage this way.
 
Just a comment on mixing greases which doesn't apply to your situation. Many new sealed bearings have a polyurea based grease with longer life. Mix that with the more common lithium greases and you will have a lubrication failure.
 
If you already dismantled the end-brackets replace with new sealed, life pre-lubricated bearings. That will be cheaper and it will make your future maintenance easier.
 
Do a search on this site for some of the buzz words that have been used in this thread. This topic has been covered very well previously in Eng-tips but I am not going looking for it for you.

rmw
 
Dale7905,
"1/2 HP, single phase, capacitor start motor with ball bearings on the rotor shaft"
Above suggestions are sensible, but with fractional size motor i would rather replace it with new one than recondition it. Ball bearing, such 6204 and below, is inexpensive and it'll never isn't burden you much.
 
Unless this is a weekend garage project for some hobby, I agree with billybry. If you are going to rely on this machine, I would replace it as long as a suitable replacement is readily available.
Many of these smaller machines were manufactured for an OEM and have minor modifications which render them difficult to replace except for going back to the OEM

Respectfully concerning the regreasing process, I have seen poor results with pumping grease until the new grease flows from the pressure release opening. We do not usually look at motors this small but on larger motors, the typical grease relief tube is 1/8" pipe thread and on the ODE on a TEFC unit, there is usually an extended tube to clear the fan cowl. This pipe often offers more resistance to grease flow than the inner seal of the bearing cap forcing grease into the windings. This problem is compounded if EP grease is being used as many of these greases are conductive.
One approach I have used requires that the motor be deenergized. Remove the drain plug, clean out passage with a pipe cleaner and pump fresh grease until evidence of the new grease shows up on a clean pipe cleaner.
 
Hi All,

Thank you all for your comments. You've given me a lot to consider. This particular project is a 'hobby' type effort for the moment; however, I'll probably find a good use for the motor in my workshop when I'm satisfied it will work well. I'm leaning toward replacing the bearings as many have suggested ..if I can get the bearings off the rotor shaft. I haven't tried getting the bearings off the rotor shaft yet. After reading some of the other threads on this site I'm wondering if I may have to heat the bearings somewhat if they are what (I guess) one would call a 'shrink fit'. I'll then look up some local motor repair places and internet sources and see if I can locate the necessary bearings. If getting the bearings off the shaft proves too much for my mechanical abilities I'll resort to trying to re-lubricate them.

Thanks again.

Dale7905
 
One of the fastest ways to remove a pressed bearing from a shaft is to position the bearing on an anvil and hit it, hard, with a big hammer. Eye protection is mandatory. One blow will shatter the outer race and probably distribute the cage and the balls around the shop. One more blow will shatter the inner race.

Of course, if you hit anything _but_ the bearing, it could also be a very expensive way to remove the bearing.

For an axle bearing, a 5 lb. hammer is about right. For fhp motor bearings, a 2 lb. hammer should suffice.



Mike Halloran
Pembroke Pines, FL, USA
 
I would never advocate removing bearings using the method described....sorry Mike its a hit and miss method at the best of times and just too dangerous. You must agree it presents a serious risk both to the operator and the machine. Anyone doing anything like that in my shop would be hauled into the office for "words".
Dale? I find the easiest and safest way is to place the rotor horizontaly in a soft-jawed vice with the back edge of the bearing flush with the ends of the jaws, then with 2 crowbars or tyrelevers, one in each hand flick the bearing off using the jaw ends as a fulcrum. You will be surprised just how little effort it takes.
 
It's a hit and hit method.

If you miss, you buy a new motor.

Agreed it's dangerous and risky, but crowbars never fit right, there's never a fulcrum in the right place, nobody can ever find the real bearing puller when you need it, and small motors are often designed in such a way that real bearing pullers won't fit anyway.





Mike Halloran
Pembroke Pines, FL, USA
 
Without seeing Dales motor we can only speculate on the best and most appropriate way to remove the bearings, however there will be a way to do it. I have yet to see a bearing on any motor shaft that cannot be removed regardless of size.
 
Generally speaking, any removal method may damage the bearings, either by breaking them or applying severe axial loading across the balls from a puller on the outer race moving the inner race. That said, the smart thing is to (1) not remove the bearing unless you're replacing it, and (2) use a tool (or piece of pipe) that only contacts the inner race when pressing the new bearings onto the shaft.
 
If you cannot conveniently access the bearing with a puller, sacrifice the bearing by cutting it either with a cutting torch or friction cutting disk or even a side grinder, whatever you have.

When you have cut the inner race, with the now C shaped secton and the heat, it should slide off, if not, cut the other side.

Sometimes the smaller motors are much more of a problem than the larger ones.
 
Grinding through the inner race will allow its removal but its almost certain you will damage the journal and possibly the shoulder by cutting into it. Burning through with oxy-acet` presents the same risks. Its a frowned upon practise in the trade. It could lead to a poor bearing fit, excess vibration and reduced bearing life. If you are prepared to accept the risks with your own machine thats your perogative but its NOT something we do when repairing/overhauling clients machines under any circumstance.
 
If the bearings are smooth running and quiet, I would forget about relubricating them and just use the motor as-is.
If the bearings start to show signs of distress, change them out for new, prelubricated, sealled bearings. Most bearing sizes are readily available as open, or sealed, prelubricated.
In industrial applications ball bearings will run 24/7 for several years.
respectfully
 
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