Crompton Parkinson 1/2 - 3/4 motor bearings

Hi

Does anyone know if Crompton Parkinson white-metal motor bearings were line-bored on assembly? The reason for the question, the front bearing on the (new to me) Super 7 motor is a bit worn in the direction of the belt tension, and therefore a bit noisy. The bearings appear to be unobtainable, at reasonable cost, as advised by Brook.

I've extracted a rear bearing ( Vanwall Products - in good condition being still a close fit on the shaft) from a spare motor. I made an oilite bearing as a replacement as an experiment to test longevity. The oilite bearing was first bored and then the outside turned on a mandril for accuracy, but the motor locked up until I resorted to some 'fitting' to ease the new rear bearing.

I now have a spare bearing to hand and the fact that the shaft in the Super 7 motor is not worn, replacing the bearing might do the trick, however, I don't want to knock-out the worn bearing before being sure that the work stands half a chance of succeeding. I can't just swap the front covers because the front bearing in the spare motor is worn in a similar way.

Regards

CotswoldsPhil

I think I've answered my own question - Are Crompton and Parkinson white metal bearings line-bored, I think the answer is yes...

I remounted the 17mm mandril I used to make the oilite bearing and clocked the white metal bearing I removed from the spare motor - the bearing slips nicely on the mandril but the outer shell runs out by 0.3mm or 0.012 inch - quite a bit. So it's going to be a bit of a lottery swapping the bearings - some thinking will be in order.

CotswoldsPhil

From a production viewpoint line boring seems an excessive faff as compared to simply making things accurate in the first place. To line bore the motor case needs to be assembled empty, bored, marked for re-assembly in the correct orientation, then disassembled so the motor can be built up. Sounds an unlikely business especially if the boring were done, as it should be, before the electrics were installed.

I've had a couple or three plain bearing motors apart and never made any attempt to keep the front plate in its original orientation and had no running or bearing issues. I could have been lucky but I doubt it. Back plate with the connections naturally has to go in the right way.

I don't know how accurately the end castings were made in the first place but it seems more likely that the snug fitting recess into which the main body slots would have been machined first and the bearing shell bored concentric to that. If you are going to bore a plain bearing to size after fitting "close" will be perfectly adequate for the original hole whilst the extra effort and expense of "dead nuts" would be a complete waste of production line time. All depends on production set-up and machining sequence.

Clive

Edited By Clive Foster on 03/09/2014 17:29:44

They aren't cast in position, are they?

Neil

Hi there, CotswoldPhil,

Oilite bearings are sintered bronze - the sintering gives them a porous structure which is (ideally) vacuum filled with oil.

The makers' 'how to' literature, as far as I can remember, said that reaming to size after assembly is a no-no because the reamer 'smears' the bronze, closing up the pores and impeding, if not totally preventing, the oil reaching the bore. Presumably, the same no-no applies to boring?

The specified fitting method is to insert using a stepped mandrel whose section in the bush has the right diameter to control the finished bore.

Best regards,

Swarf, Mostly!

Hi Neil, no they are split mild steel backed about 1.5mm wall and pushed out very easily, but the white metal internal diameter is not concentric with the outer by about 0.3mm 0.012 in old money, making me think that they were sized in situ. by some method.

Hi Swarf,Mostly! The originals are white metal (VP Products) - I made an oilite bush as an experiment using very sharp tools to prevent rubbing, it was also soaked in oil overnight. The bush has been installed in the spare motor and so far I have not seen any bronze slush near the bearing, but time will tell. I'm not sure about the compatibility of a non hardened shaft running in an oilite bush albeit at the rear of the motor with no side load from a belt. Fortunately there is an oil passage directly to the shaft via a hole in the bearing.

The idea was to use an unworn rear bearing from a spare (not so good) motor to replace the worn front load bearing end of the lathe motor.

CotswoldsPhil

The bearings are Vandervell, not Vanwall, and they are still in business. although I am sure it is a long time since they made that type of bearing, you could ask them. Have you tried the new bearing in position and then rotated the motor end cap to see if the rotor frees off. Are the end caps pressed metal or cast, and what type of flange is there where the end cap meets the stator housing?They should align without any reaming, but it is possible that the end cap is distorted or the flange is damaged. I can remember that we used to bump the end caps with a rubber mallet whilst the through bolts were loose to line everything up. Is the binding in the bearing, or is it the squirrel cage touching the stator? I uset to service a lot of this type of Crompac motor which was fitted to all sorts of small industrial machinery. can you post some pics?

Phil

East Yorks.

Hi Phil,

The end caps are cast alloy, with a machined register for the stator and with the bearings pushed into a bored hole. I'm working on the rear so unable to rotate the cap. Having eased (bell-mouthed) the experimental rear oilite bearing the spare motor is running as expected. I reassembled the casings in the same alignment and bumped everything up with the plastic hammer whilst tightening the 4 bolts. Whats odd, is that the hole in the Vandervell (thanks for the correction) bearing, is NOT concentric with the outer diameter, it is out by 0.3mm when clocked in the lathe on a true 17mm mandril. However the oilite I made was concentric.

I'll take some pics later tomorrow - the workshop is all bedded down for the night.

Thanks for you interest

Regards

Phil H

Vandervell steel backed white metal bearings are ready to fit in automotive applications, the instructions warn against scraping. I would have thought that if they can make shells that accurately, a split bush for a motor would need no further work after installing. The only precision tasks required would be the hole size and concentricity with the register. My vote goes for them being presized to give the correct clearance after fitting in a correctly toleranced hole. Your new bush may have closed up on being pressed in. Many bearings rely on the fit in the housing to bring them to their designed fit, even ball races can be ruined by too small a housing or too tight on shaft, Torrington needle rollers certainly need a tightly toleranced hole and shaft to achieve the correct running fit.

Mike

Edited By Michael Poole on 03/09/2014 20:42:14

Hi Phil, Yes, I read what you said, .012" out...........that is a long way and you would not expect it or anything like it on such a part. It sounds to me like you have done everything you should have. This is odd because I can't remember ever seeing this problem before, and we did do quite a few of these, and we used to literally bang them back together with no problems at all! Very annoying. I will wait for pics.

YorkshirePhil

Hi Phil,

Would the eccentricity be due to wear? With the bearing installed in the housing is the hole round? A pair of internal calipers will easily detect an out of round condition. If the shaft is oiled this can flatter how good the fit is.

Mike

It's perhaps slightly off-topic, but this short paper by ABB is very interesting!

MichaelG.

I,m pretty sure its a misalignment problem. These motors are turned out like shelling peas, they were cheap and cheerful. The stators are wound and the rotors are just popped in. When dismantling any motor its is important to mark the stator and end cover so that correct alignment is established, otherwise binding takes place.(Two parallel scriber scratch marks one end, stator to end cover, and single scratch mark stator to end cover the other end) I suggest you slacken off all 4 bolt and rotate the rotor by hand and tighten 2 bolts diagonally a bit at time. You may find that a tap here and there with a soft mallet will move things so that the rotor moves freely.Ted

Unless an oilite is of the self aligning (spherical) type, the bore will be over size until it is pressed into a hole with a prescribed interference, it should be pressed in with a mandrel that fits the bore at the same size as the shaft that will be fitted in the bearing. You were lucky that the bearing stayed whole when you bored it, I'v tried, and had the bearing collapse. Even a very sharp tool smears the particles and the bearing essentially becomes a plain bronze, or cast iron (depending on type) bearing.

Ian S C

Hi Everyone,

I'm not ignoring you, I've just got back from domestic duties and will be going into the shed later this afternoon.

I also must also apologise for 'shouting' a bit last night - I think I had overdosed on information...

Thanks for all your interest - back shortly with some progress.

Regards

Phil H

Evening all,

Thanks for your patience...

The bearing as removed from the rear of the spare motor.

I've taken a load of photos (they are in an album) to illustrate the problem - do have a look, it tells the whole story, no point in repeating them here, but I will include the most telling pictures here. The bearing does not appear to be worn.

The other end is similar.

So, I think I might have stumbled across a reworked motor which has a distorted rear cover, I remember it having a slight wobble, but no obvious play, which is why I removed the bearing in the first place. Just my luck. However, the front cover off the spare motor might do the trick, it appears to have a bit of bell-mouth wear but much less that the S7 motor which is visible when the belt is tweaked. I will try the front cover swaps tomorrow and give up on the spare bearing idea - well, I might as well put it back in the spare motor where I got it from, removing the experimental oilite I made.

Once again, thanks for all your input - the knowledge out there is tremendous.

Regards

Phil H

White metal bearings are made by passing a broach through them, possibly gang broached in one go. I think the broach was not drawn back through the bearings. Split bearing were placed in a housing which matched the finished size before broaching. Some of them were heavily copper plated before the white metal lay. This may explain why the hole is off center. I very much doubt it was done in the motor with both ends attached as that is too much work. I have always admired the excellent surface finish on white metal bearings.

Clive

Hi Clive,

Thanks for the sizing information, that could help explain the unworn off-centre hole in the bearing I have to hand. Could it be that the split bearings, pre-formed with oil passages, were first pressed into the end-caps and then broached with the end cap+bearing in a jig, registered on the machined rim which locates with the stator? This would correct any potential inaccuracy in the end cap die-casting. This bearing, even after 50 years, is still a nice slip fit on the motor shaft.

Regards

Phil H

Edited By CotswoldsPhil on 05/09/2014 09:30:28

And Finally...

I've swapped the front casings between the spare 1/2hp (a bit worn) and the 3/4 hp on the Super 7 (a lot worn). I had to adjust the end-float with some shims, but what a difference to the Super 7 motor, a bit less tension on the new belts - I don't do heavy work. The (new to me) Super 7 motor is now nice and quiet and running to my satisfaction like the 1/2 hp motor on the ML7.

I will miss the trusty ML7, it's up for sale after 45 years, so I've put some pictures in an album to remember it by in years to come.

Once again many thanks to all contributors.

Regards

CotswoldsPhil