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10-24-2007, 07:45 PM #1
I am checking the bearings on an old 3 phase motor for my new lathe. there is grease EVERYWHERE, as in the joker that had it last took using his grease gun way to seriously. I was wondering what is good to clean that off the windings and all without damaging the enamel/laquer that holds it all together? or do I just clean off the majority carefully with a shop rag and not worry about the rest.
The bearings are unsealed ball bearings, and I was wondering if I should just get new double sealed bearings or clean the old ones and not use quite so much grease. motor is from the 40's, and was working I think. I'm checking the windings for proper resistance befre bothering to do much more.
10-24-2007, 08:32 PM #2
My Dad has rebuilt probably ~25 single phase "basket case" fractional HP motors as kind of a hobby. The older 8XXX bearings are easily replaced by double-sealed 62XX bearings in all but 1 case.
I think I would carefully wipe down the innards, after all the excess hasn't damaged it thus far, a solvent is going to be hit or miss.
Nice thing about a 3ph motor is there are no capacitors or centrifugal switches to have to work with.
10-24-2007, 09:12 PM #3
Use white spirits and remove as much grease as possible.
Bake in an oven to dry properly.
10-24-2007, 09:29 PM #4
It seems to be a trend on any motor with a zerk or two that they inevitably end up pumped full of grease to overflowing. Too many times I've cracked open a motor and found shielded or sealed bearings inside but some dim bulb didn't cap off the grease ports.
I've had good luck by removing the majority of the grease with rags, putty knife, etc. Then I use clean sawdust, an old paint brush, and a shop vac to remove the rest of the grease. Just work the sawdust into the nooks and crannies with the brush and vacuum it clean. Rinse, lather, repeat till the extra grease is all gone.
Most of the motors I've done this too came out of direct drive woodworking machines so there is always an abundance of sawdust around. I would guess there are other products that might accomplish the same thing, but the sawdust is pretty benign for the varnish, easy to dispose of, and available so I've never bothered to look any further.
10-24-2007, 11:21 PM #5
do you mean stoddard solvent?
are there other solvents that will not melt the varnish, i.e. paint thinner, etc?
10-24-2007, 11:31 PM #6
those are all pretty much one and the same. stoddard, white, paint thinner.
10-24-2007, 11:31 PM #7
Mineral spirits paint thinner. It's very suitable for removing grease and oil from motor windings and most anything else not made of styrene plastic. Dry the stator in a warm oven if SWMBO will let you. Otherwise cover it with an old towel and leave a lit 100 watt light inside.
Treat the rest of the motor as plain old mechanical parts.
10-25-2007, 12:02 AM #8
I second Forrest's suggestion, I rebuild motors often. Paint thinner is cheap. I wouldn't scrape windings with anything metal. Maybe carefully with a plastic putty knife for the big chunks but that still makes me nervous, especially on old windings where the varnish could be a bit brittle. Usually I will take a spray bottle and soak it, go away for a while to let it soften, then get after it with a tooth brush. Something else to consider, those cheap siphon parts cleaning guns that they sell at Home Depot or Lowes work great. One more thing, before you spend your effort, if you have a megger to check leakage to ground, that's probably a more meaningful test than resistance if it was running to start with. As you surmise it's good to make sure you're not wasting your effort on a questionable motor.
10-25-2007, 11:32 AM #9
I assume it was running, but I had to cut some power leads to move it. the building this lathe was in had no power, and I had to remove some wiring and other stuff to keep the flexible conduit from getting crushed in the move. the 3 phase motors I have messed with in the past have seemed pretty bullet proof. I guess I now have one more excuse to buy a megger, however.
10-25-2007, 11:54 AM #10
If your buying a megger, plot a graph:
insulation resistance vs time/temperature.
Take readings evey 1/2 hr, when the insulation resistance readings remain stable, remove motor from oven and let cool.
Check insulation resistance when cold > 20M ohm would be nice. Regulations permit a minium of 0.5M ohm.
10-25-2007, 01:23 PM #11
Having been there and done that a couple of times (including finding chicken bones in the end bell of my radial drill), I'm with the mineral spirit crowd. I wouldn't use anything to scrape at the windings, mineral spirit soaked rag at the very most for really caked on areas.
The ideal way to go at this is with an oil fogger gun. This is kind of a cross between an oil can, a paint spray gun and a pressure washer that hooks to your air compressor. I think HF has a version that will work for you. Just fill it with MS and blast everything. Baking is ideal, Forrest's light bulb will certainly work, but I just set mine outside in the Alabama summer sun for a couple of days. The idea is just to completely evaporate the mineral spirits in this case.
10-25-2007, 01:30 PM #12
And speaking of grease in motors...
I have seen many plain bearing machine tool parts and motors with grease fittings screwed in to replace Git's oil cups. This is about the same as throwing out the oil sump and pump on your car engine and putting grease fittings on the mains and rod bearings. It will ruin the bearings.
If your motor has plain bearings and ring type oilers, but somebody has installed grease fittings; put new bearings in it (the old ones are going to be toast) and order a set of Git's cups for proper lube.
10-25-2007, 02:11 PM #13
I have a drying box that consists of 4 100W light bulbs hanging in a ply wood box with plain porcelain light fixtures. gets up to a little under 200F, and seems to work pretty good for this kind of thing.
thanks for the tips,