Crompton Motor bearings

[David PayParticipant @davidpay30509]

I am very new to this site and I hope someone can help me please. Before posting this I have read the various threads on the site but still can't find the answer to a question which, I am sure, must have arisen for many others.

I have just acquired a well used Super 7 (1975) and the motor bearings seem to be shot. There is significant end play on the shaft and considerable noise when the motor is running.

Its a single phase 3/4 hp. I am aware that I could replace the motor with a 3 phase unit and VFD, but that means a significant spend.

Is it possible to buy replacement bearings for this motor?

If so, where please?

If not, are there any relatively simple alternatives.

All serious suggestions welcome, but please bear in mind that my engineering skills are limited. .

[David PayParticipant @davidpay30509]

[larry PhelanParticipant @larryphelan54019]

Crompton are a well known motor,I have one on my homebuilt saw bench for the last 50 years. Had to replace one bearing when I got it second hand [no idea how old it is ] and it,s still running.

Any bearing supplier should be able to supply new bearings and they are not dear. Those motors are simple to strip down,take off the end cover [where the connections are] and withdraw the shaft,with the bearings on it. Take it to your bearing supplier [there is one somewhere near you,since they are everywhere ] they will measure the bearing,I would guess it,s 5/8" shaft,I forget the outside measurement of the ballrace,but they will check that too.

It,s then just a mater of removing the old races and fitting the new,and away you go for the next 50 years or so !

I did not have a proper pullers but I made up a simple one which did the job. Ask around,someone must have a pullers,failing that,try your local garage,they should have one.

As an aside,those motors have a switch which controls the starting coils,this cuts out once the motor gets up to speed,now,when the motor is switched off and the speed drops,you should hear this switch cut out with a clear click !! If it does not,it is stuck,and needs to be cleaned,no big deal,just be aware of it. Happened me a few times with my sawbench due to sawdust,should not be a problem on your lathe.

Hope this is of some help to you. They are a great motor,worth looking after.

[MuzzerParticipant @muzzer]

Assuming it's a standard bearing, the size should be described by the number on the bearing face.

I've used The Bearing Boys before and they were quick and easy to deal with. Not worth taking your chances with the various cowboys on ebay etc, as many of the products are totally worthless and barely usable even as skateboard bearings.

Murray

[larry PhelanParticipant @larryphelan54019]

I agree,forget Ebay and the rest,go to a proper supplier and get the proper bearings,remember,you will have these for the next 40 years,I,m not kidding These motors are like silk ! Many happy hours turning,when you get it up and running.

PS Go for a good make such as SKF or something similar,no junk !

[Nick HulmeParticipant @nickhulme30114]

Check your local area for "bearing services" companies, I'm very lucky to have City Seals & Bearings almost on my doorstep, if they don't have it they can get it and they are a great company with excellent staff.

[john fletcher 1Participant @johnfletcher1]

Usually its the bearing at the drive/ pulley end which fails, at the non drive end its often just a bush ,which you can drive out by removing the cover. Before taking the motor apart scratch mark across the stator to end shield, two one end, one the other, don't us a centre punch. These marks will help you to reassemble the motor so that it runs freely by a thick of the wrist. Also, check the centrifugal switch whilst you have the motor apart and be careful with those lead outs as they are easily broken. An insulation test should be carried out before connecting to the mains using a "Megger" or similar meter.John

[the artfull-codgerParticipant @theartfull-codger]

You may find that the motor is bronze bushed instead of ball races, I bought my super7 brand new from stevensons northgate Darlington[when it was a 1st class engineering supplies shop] & you paid extra for the motor,resilient mounted motors were in short supply then so myfords supplied a standard foot mounted motor,[ an absolute rubbish idea myfords!!] it allways suffered vibration, I waited my chance for a 3/4 hp resilient motor at the right price,got one for £15 assured it worked, well it did but the front bearing was noisy & worn & the shaft scored,I set the armature between centres in the lathe,skimmed the shaft & finished with 1500 oiled wet & dry [no-one admits to using emery but loads use it!!] turned up a bronze bush from home cast bronze, back together & fitted it & it's a different lathe alltogether, smooth as silk, that was quite a few yrs ago,of course you need a lathe to do it [sorry David not much help to you] I still had the old motor on.I oil it regularly.

[Clive FosterParticipant @clivefoster55965]

The one and only time I bought new motor bearings, pushing 40 years ago, I was advised to get electric motor rated bearings. Don't recall if it was my then guru who suggested this or whether it was the bearing supplier. I do know that they had bearings of the correct number in stock but not the electric motor rated type so had to go back next week.

Not a clue what the difference between ordinary and electric motor rated bearings was, too young and nervy to ask. It was made fairly clear that although an ordinary bearing would work the proper ones would be much better. These days best guess is different fit class. Don't recall any difference in price. Proper branded ones of course and, by todays standards, relatively expensive in real terms. Lost track of the motor after 25 years or so and it was still going strong then.

Times change so the distinction between motor rated and normal stock bearings may no longer be appropriate. I have heard of ordinary bearings being used with moderately unsatisfactory results. But I'm fairly dubious as to the mechanical competence of the person concerned so could be fitter error not bearing error.

Clive.

[David PayParticipant @davidpay30509]

Thanks everyone.

Looks like the first job is to dismantle the motor and see what I've got.

From the threads I had viewed, I had the impression that the bearings would inevitably be solid metal and probably unobtainable. If that turns out to be the case, I will be back for more suggestions.

David.

[HopperParticipant @hopper]

The bearings will most likely be common sized ball bearings.

If they do turn out to be bronze bushes, or sintered bronze "Oilite" types, you can buy them in standard sizes from good bearing suppliers also.

Bearings are a consumable item like brake pads and as such are designed to wear out and be replaced during the life of the machine, so plenty of replacements available.

Edited By Hopper on 20/08/2017 00:06:36

[larry PhelanParticipant @larryphelan54019]

Hi David,

I forgot to mention that perhaps the belt was too tight on your lathe,bearings dont like that,it gives them a hard time. I might also be no harm to check the inside of the belt to see if it,s cracked or frayed. I would be inclined to replace it anyway. With new bearings and belt and the tension set right,you should be OK.

[Nick_GParticipant @nick_g]

.

I replaced the bearings in the Brook Crompton motor on my lathe a couple of weeks ago. This was a 'preventative' exercise as the cost of new SKF ones was very low. This low cost was probably down to them being a standard bearing of 17x40x12 The number was stamped onto them but I cannot remember it. – Even if the number is not stamped if you take the old bearing to a reputable supplier they will measure it for you should you be in any doubt yourself.

(The 'workshop walk' video I did the other week the view of the back of my lathe can be seen without a motor fitted and elsewhere the motor can be seen briefly in a stripped state on a bench.)

Nick

[SillyOldDufferModerator @sillyoldduffer]

Posted by Clive Foster on 19/08/2017 22:06:56:

…

Not a clue what the difference between ordinary and electric motor rated bearings was, too young and nervy to ask. It was made fairly clear that although an ordinary bearing would work the proper ones would be much better.

…

Clive.

Joining the dots on something I read recently about spiky volts from VFDs potentially damaging the bearings of old motors, I suspect this is to do with what happens to a bearing when an electric current passes though it.

There are many reasons why a motor's rotor could be electrically charged. Even limited electric action would soon damage a bearing surface, and there might even be spark erosion. Once electricity has roughed up a running surface the bearing will wear rapidly.

I think the design of modern motors (circa 1970) has been altered to prevent rotor current earthing through the bearing surfaces. It could be done by either insulating the bearing itself or by providing a conductive route bypassing the bearing parts. Inside a bearing, possibly the metal shield used to keep muck out of ball bearings would be enough to stop damage, or some trick with graphite or a brush.

I'd guess that whatever is done to make a bearing suitable for use in an electric motor or generator probably makes it slightly stiffer than an ordinary one. The extra drag would be unwelcome in other applications, hence the reason for two types in the same size.

Dave

[HopperParticipant @hopper]

Posted by Nick_G on 20/08/2017 09:38:03:

.

I replaced the bearings in the Brook Crompton motor on my lathe a couple of weeks ago. This was a 'preventative' exercise as the cost of new SKF ones was very low. This low cost was probably down to them being a standard bearing of 17x40x12 The number was stamped onto them but I cannot remember it. …

Nick

6203. Pretty standard bearing used in squillions of electric motors and also motorbike wheels and many other apps.

[Clive FosterParticipant @clivefoster55965]

Looks as if electric motor / non electric motor bearing difference is a combination of clearances and quality.

There is an EQM quality rating covering electric motor bearings similar to the ABEC precision bearing one.

According to NTN a C2 or CM internal clearance rating is most appropriate for small electric motors **LINK** , interesting but get the wet towel and aspirin bottle out first. NTN also say "In most electric motor rebuild applications a C3 clearance can be used in place of a normal clearance." **LINK** which is worth a look to help clarify some of the confusing designation stuff.

Normal clearance is CN.

I guess really its down to most electric motor bearings being expected to have 100,000 – 200,000 hour running lifetimes with, probably, no re-lubrication. So higher quality is probably desirable.

If buying from the professional suppliers I think it always best to say what you intend to use it for. Especially if its something truly generic like the aforementioned 6203 which can be found in all qualities from compressed cheese to "fine for your intergalactic robot spaceship sir".

Clive.

Edited By Clive Foster on 20/08/2017 12:11:06

[David PayParticipant @davidpay30509]

OK, I've bitten the bullet and the motor is now in pieces. As I originally feared, the bearings are solid metal ("oilite?&quot. Now its off to the local bearing suppliers to try my luck. I will post a couple of photos later but suffice it to say that there was an enormous amount of general muck and a not inconsiderable quantity of swarf inside.

A couple more questions at this point please.

1. how do I get the bearings out of the endcaps of the motor. Not sure whether to prise them from the inside or hit the outside to drive them in. If the latter, am I correct in thinking I need some sort of hollow mandrel/pipe more or less of the OD of the bearing to drive them. The centre looks far too flimsy with wool packed around the bearing ends but with my motor in bits I have no way to turn a suitable tool..

2. Assuming I can buy replacement bearings, how, if at all, do I adjust out any end float when I reassemble the shaft.

Thanks again

David

[Clive FosterParticipant @clivefoster55965]

If the old bushes aren't terribly tight a large rawlbolt or rawlstud concrete anchor can make a sufficiently effective expanding manure to pull things out with. I keep a few with suitable part split alloy sleeves to extend their range in my "get out of jail" drawer. Sleeves save getting expensive big ones. Piece of wood drilled for the anchor with the outside hacked down to roughly right size to go in the bearing would do for one time job. If you can get at both sizes a simple wood screw should expand the end of a reasonably fitting wood dowel enough to get enough grip to drive it out.

If its an alloy end dropping in boiling water or warming up with a paint stripper that gun will expand things a bit loosening the fit.

Clive

[SillyOldDufferModerator @sillyoldduffer]

Posted by Clive Foster on 20/08/2017 12:10:47:

Looks as if electric motor / non electric motor bearing difference is a combination of clearances and quality.

…

 

Clive.

 

Hi Clive,

Apologies for being unbearably smug but I did find this in support of my guess on the NSK website:

'A major obstacle to achieving extended maintenance free intervals is electrical erosion. This occurs when ‘stray’ electric current flows through the motor bearings to earth. The result is damage to the bearing, the extent of which depends upon the magnitude of the current and the duration of the conditions. The damage, known as electrical arcing, is usually in the form of tiny craters and micro welds on the bearing raceway and rolling element surfaces, which results in premature bearing failure.

One solution to the electrical arcing failures is the use of ceramic coatings or ceramic rolling elements in the bearing design, which provide electrical insulation from the shaft. Ceramic coatings are often applied using a plasma spray. The ceramic coating is treated with an acrylic resin to seal the surface and prevent the ingress of moisture. This coating also provides additional protection against strong alkalis and high temperatures used for washing the rolling stock.'

Interesting. Anyway, all David Pay needs to say though is that the bearings are for an electric motor. If he can't get any or the repair otherwise goes completely pear-shaped, a new 3/4HP motor can be had for about £100.

Dave

Edited By SillyOldDuffer on 20/08/2017 17:59:48

[Nick_GParticipant @nick_g]

Posted by SillyOldDuffer on 20/08/2017 17:57:44:

a new 3/4HP motor can be had for about £100.

Dave

.

I would like to know a source of a 3/4 – 1 hp B56 framed motor for those coins.

I think B56 is an imperial frame designation. But I wonder if there is a metric one that would fall into that size even if the pulley had to be changed.

(hope this is not considered a thread hijack)

Nick

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