Motor bearings

[Paul BarterParticipant @paulbarter66156]

Hello all, can anyone out there throw some light on this please? I am refurbishing a 1950s Brooks Crompton Griffon three phase motor for an elderly Jubilee lathe.The bearings as usual, were caked with congealed grease and wood dust, but as I replace these relatively inexpensive bearings as a matter of course, even SKF or FAG are only a couple of pounds or so I pulled the bearings off and then decided to see how sh***ed they were after 60 odd years of neglect. However after washing with petrol,drying and oiling they seemed fine, with no trace of roughness at hand spinning speed.This pompted a more detailed examination and I then saw that each bearing (LJ17 RHP), 6203 equivalent, has some numbers etched on the outer race, only one bearing was just legible, but the numbers seem to be similar on both bearings as 003 bc?. My question is this, are these special bearings? should I be replacing them with anything other than standard clearance non budget bearings? The motor is currently three phase star (440V),shortly to be delta (220V) and either run from an IMO inverter or one my Frankenstein Steinmetz connections.I would hate to negate the quality of this motor for the sake of a few pounds, if special bearings are required to ensure reliability comparable to that already achieved.Thanks in advance to anyone who feels able to enlighten me.

Edited By Paul Barter on 24/08/2013 23:19:07

[Paul BarterParticipant @paulbarter66156]

Please, what do these markings signify?

[John Stevenson 1Participant @johnstevenson1]

It's the date

Three years Before Christ…………….

[Michael GilliganParticipant @michaelgilligan61133]

Paul,

There's an explanation of [modern] RHP numbering, here

… but I fear that John may be right.

MichaelG.

[oldveloParticipant @oldvelo]

Hi Paul

One of my jobs when working as factory engineer was overhaul of machinery and motors.

The normal procedure to replace open race grease lubricated bearings was to fit in your case a

6203 2rs bearing with a "Wave Washer" in the housing opposite the drive shaft.

You can expect many years of running from them.

1969 Ransome's joined with Hoffman's and Pollard's as subsidiaries of RHP Limited.

One small note it would appear that your motor bearings were replaced some time after that date.

Eric

[Paul BarterParticipant @paulbarter66156]

Thank you all for taking the trouble to reply to my plea,

Erics suggestion is the logical course and and will follow his recommendation,thanks to Michael and John too, although this motor doesn't seem to predate Mr Faraday, even though the fixings are imperial and it has sufficient metal in it to to make a starship and RHPs numbering system does not cover etch pen markings added on assembley.

Thanks again to all

[_Paul_Participant @_paul_]

You may find etched markings on modified bearings Fafnir do this.

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Brooke Compton standard replacement bearing type 3 . Apart from the identifier it’s an ordinary general purpose bearing .

Regards ,

MikeW

PS : Why has text entry box shrunk to 4 cm by 3 with no editing features ????

Edited By MICHAEL WILLIAMS on 25/08/2013 11:24:47

[Paul BarterParticipant @paulbarter66156]

Hi Mike, Can't help with the box, but thanks for the bearing clarification. My conscience is clear for replacing these old bits with SKF 6203 2RS. They will live on as toolpost work aligners

Thanks again

regards Paul.

[Paul BarterParticipant @paulbarter66156]

Hi Mike, Can't help with the box, but thanks for the bearing clarification. My conscience is clear for replacing these old bits with SKF 6203 2RS. They will live on as toolpost work aligners

Thanks again

regards Paul.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by MICHAEL WILLIAMS on 25/08/2013 11:23:22:

PS : Why has text entry box shrunk to 4 cm by 3 with no editing features ????

Edited By MICHAEL WILLIAMS on 25/08/2013 11:24:47

.

Mike.

I think it has to do with Javascript settings

Have a look at my posting on the "Another way to enjoy your hobby" thread.

[ towards the top of the fourth page ]

MichaelG.

 

Edited By Michael Gilligan on 25/08/2013 15:21:24

[Tinkerer58Participant @tinkerer58]

If the marking is C3 it means that it has a C3 clearance. If your motor housing is made of an alloy material I would suggest using a C3 clearance bearing. The reason for a larger clearance bearing is that during extended operation the moter heats up and the alloy material and the steel bearings expand at different rates, the larger clearance is to cater for this so the internal clearance on the bearing does not get too tight and increase the friction causing the bearing to over heat. Once the bearing over heats the lubricant become too thin and becomes inefective or starts to leak out as it gets more liquidous cause premature bearing failure. I have been in the bearing industry for 15 years as a technical and applications engineer. I trust this helps you.

[Les Jones 1Participant @lesjones1]

Removed due to duplicate post.

Les.

Edited By Les Jones 1 on 26/08/2013 14:37:18

[Les Jones 1Participant @lesjones1]

Hi Tinkerer58,
I would have thought that the effect of the different coefficients of expancion of steel and aluminium would cause the bearing to become looser in in the housing. Aluminium has a larger coefficient of linear expansion than steel so the diameter of the housing will increase more then the diameter of the bearing making it looser as it heats up.

Les.

[Paul BarterParticipant @paulbarter66156]

Hi Tinkerer58 and Les,Thanks for your input, This motor has cast itron end bells and the bearing housing at the pulley end has a wave washer. The bearing are retained by their firm push fit on the shaft and located by circlips, the rotor appears to be able to move a few thou axially within the limits of the wave washer,presumabley to cxope with any thermally induced changes. This motor only turns at a leisurely 1450 rpm, so low surface speeds within the bearing and the radial loads are loads are piffling, on a wood lathe the torque of the motor is resisted only by my lily white hands holding a tool against a rest. The usual cause of bearing failure in my experience is lack of, or contamination of the lubricant, wood dust is surprisingly abrasive, many woods chosen for ornamental turning contain silicates, ie sand, they demonstrate their abrasive qualities by the need to sharpen even M2 tool steel chisels with greater frequency when turning teak for instance. The rest of woods at best still produce an absorbent dust which rapidly clogs bearings, preventing the lubricant from circulating within the bearing assembley.Presumabley the open bearings originally specified relied on grease be regularly being injected and contaminated lubricant being replaced,Rubber sealed (2RS) beings with adequate, not excessive quantities of the correct grease neatly side step this vulnerabilty as oldvelos suggestion.

Thanks to you all for taking the trouble to respond

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, I wouldn't worry to much about getting bearings with a larger clearance in the rolling elements which is what a C3 is. If the bearings were C3's then they would be clearly maked as a suffix after the bearing designation e.g. 6203 C3.

A open 6203 bearing with grease lubrication has a limiting speed of around 24,000 rpm depending on the manufacturer. A 6203 2RS will have a limiting speed of around 11,000 rpm. These figures are general and are dependent upon dynamic loading etc.

I would say that the motor manufacturer got thier sums right, so either of these bearings will be well within suitability.

The main factor for long life of bearings is the ability for the heat generated by the bearing to be in equillibrium to the heat dissapated from the bearing to the shaft, housing and lubricant.

If the bearings can be regreased externally, I would use a bearing with just one seal, with the seal side towards the inside of the motor and pump a little fresh grease into them occasionally.

Regards Nick.

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