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MG Midget and Sprite Technical - Rear hub bearings with wire wheels

I'm doing some work on my friends 69 MG midget to get it through the MOT.

There is some welding around the chassis leg, handbrake adjustment, replacing the leaf springs and the offside rear wheel bearing....

There was considerable play in the old bearing despite only being two years old. I fitted a new bearing, O ring and gasket. The play is reduced but there is still enough to bother me. I think its marginal for an MOT personally.

Applying the handbrake and grabbing the sides of the wheel shows little or no play. So i *think* that rules out wear on the splines?

The bearing was press fitted into the housing which was a good tight fit.

Where else should I be looking for play other than the bearing itself? My friend bought the bearing from Moss, has anyone had any problems with these?
Chris Madge

It's posible Moss are supplying c3 grade bearings. C3 has greater than normal internal clearance. They are suitable for higher speed/temp applications. They attain correct clearances when running. I've got a set I took out for that reason. Good japanese bearings otherwise.

But it's not much play, and with mot exemption, I'm not too worried.

Ideally useCN (C0). C2 is to little internal clearance.

CN or C0 is not usually marked. So an absence of c marking denotes CN.

I assume the inner seating is good and nut is good ?

I think I have a good S/H original bearing that you could try.

Could try bolting a length of dexion etc across the hub when installed and check for movement.

richard b

Richard I'm confident the seating of the bearing is good. But is a little chewed from previous 'mechanics' but it tightens down just fine with a 3/4 drive 4 ft breaker bar.

It sounds like the bearing Moss uses is a bit sloppy then?
Chris Madge

ISTR it was noted that the rear bearings were standard metric size and therefore available from major bearing suppliers - I must measure some up to check.

I would assume if the wheel bearing is slack the halfshafts / diff splines are going to wear much more rapidly as the wheel flexes.

richard b

"I would assume if the wheel bearing is slack the halfshafts / diff splines are going to wear much more rapidly as the wheel flexes."

Yes that sounds plausible.

When I did mine I remember buying good quality bearings from a bearing factor. And touch wood - mine are fine 3 years later.

It may get through the MOT, otherwise we might have to shop for a better one.
Chris Madge

Well as they say 'you know where I live' !!!

It's available if you want to collect - only changed it out when I rebuilt my axle years ago - so sat in the garage waiting for it next adventures !

richard b

Thanks Richard I'll bear (pun intended) that in mind.

I wonder if the half shaft is worn where it passes through the bearing.
Chris Madge

Interesting Anon - just found a couple of NOS Moss kits dated 2006 ! one has a NSK bearing (marked England) and C3 - he second one only has a number.

Chris, The halfhaft as I understand it does not contact the bearing - only via the flanges/hub.
If it does there would be a lot of flex going on.

richard b

The bearing number is 6207 35x72x17mm deep groove single row.

Looking on Evil bay the MGOC have a pic of a set which is SKF and marked C3 also - whether the current stock is as the pic I don't know.
richard b

Skf 6207 CN


Yes there are lots of bearing suppliers offering both standard and C3 - my point of identifying the MGOC one is that their pic was for C3 as well as the Moss ones I have from back in 2006 - as there does not seem to be a price difference between the two specs I wonder why they go for a C3 type ?

I have some other old hubs - I'll dig them out and see what bearings are in them.

richard b

As the axle is a semi floating type the half shafts do provide a substantial amount of support to the wheel. In extreme cases, normally on race cars, the axle can fail at the outer end due to fatigue. I've had one do that on my road car.
David Billington

"I wonder why they go for a C3 type ?"

What would be useful is to see the original drawing spec' for the rear wheel bearings.

I have an original bearing that I use as a drift. It has no C designation markers on it.

It is the original RM bearing race that came out of my '66 Sprite some time in the mid 1990's. I got my Sprite in 1977, and there was no sign that anyone had ever taken the hub off before. I only took the bearing out and replaced it because the hub oil seal was weeping.

Perhaps over time, people just started stocking, mistakenly, C3 bearings instead of CN.

Or perhaps not all C3 are created equal. Perhaps some are closer tolerance than others. I have a QH set that are C3. And when I installed one it was really sloppy. They are TOYO 6207 bearings.

Why would the original bearings have been metric? The fronts are specified in imperial as seen in the drawings. So surely the rears would have been too; wouldn't they, at that point in time?

Could it be that in selecting the nearest equivalent metric bearing, additional internal clearance has crept in?

It's my understanding that rolling element bearings were developed and standardised in Europe and to metric dimensions and so have always been more common in metric sizes so cheaper. I know someone that asked the designer of a IIRC 1930s Scammell gearbox why he used metric bearings in an otherwise inch gearbox and the answer was cost.
David Billington

That's interesting David.

Found this on bearingboys website.

MJ and LJ bearings. Our Spridget rears are LJ. What does lj and mj signify? I've forgotten -- if I ever knew. Lol.

I wonder if the nearest imperial mj size would be a better choice. Just need to measure accurately an old RM bearing in inches.


Anam, LJ means light journal and MJ medium journal. As an example LJ1 is a light journal of 1 inch bore. The 6000 series are all metric.

T Mason

As the bearing is a light press fit into the hub, I think it would be very unlikely (or very lucky) to find an Imperial bearing that would fit.

richard b

Are they a light press fit though? If the hubs are in good condition, it takes a good bit of drifting to get them in. At least that's my experience. But I guess if actually using a press, it probably is a light press.

Anyway going back to just the issue of internal clearance, any good 6207 bearing should do it. If I needed new ones I'd buy some CN grade.

Interesting, thanks for the input gentlemen.

The old bearing was from Moss, and its a C3. The new bearing that went in was also from Moss but i didnt check the spec.

The car passed the MOT. The tester is sympathetic to our cars and knows the quality of some of the after market parts.

Personally I wouldnt accept the slop on my car and would be looking for something better, but its not my car. I expect Ill be changing the bearings again in a year or two!

Chris Madge

If it passed the mot, unless very high mileage is achieved in the next 10 years, I doubt that bearing will get any looser or need changing again for a long time. Can any 'wobble' actually be felt when driving it?

Also, you should have the handbrake off when testing the rear wheel for wobble by hand, either 9-3 or 12-6 is ok for that.

In addition, if there is any appreciable wear in the diff planet gear bearing surface, that could give you a false impression of how much the wheel bearing is 'loose'.

The wheel bearing was replaced with the Moss C3 just two years ago !

A fussy MOT tester will fail it I'm sure.

Good point about the diff I hadnt considered that. The diff is very likely to be worn as well.
Chris Madge

I bought the rubber sealed SKF in 1997. it is metric. No leaks no flakes in de bearing, perfect fit with some loctite 603 or 638, . Growler could not stop raving about them.
SKF part# 6207 2RS1 €10
NSK part# 6207vvc-mav2

Flip Brühl

I never really agreed with these bearings being C3 clearance, it was one of the things I made sure of when I used to do my wheel bearing kits.

As a very theoretical exercise, I drew up a standard and a C3 bearing in CAD and determined the theoretical free play for each as would be measured/felt at the wheel edge.

For a standard bearing: +/- 0.44mm (assuming nominal internal tolerances), +/- 0.75 at maximum tolerance.

For a C3 bearing: +/- 0.75mm at nominal, +/- 1.1 at maximum tolerance.

Conclude what you like from those figures :-)


I don't think the original spec was for C3. That's why seeing the original drawings would be useful.

Do(did) your kits include CN then Malcolm?

Yes Anam. I supplied standard clearance, not C3.

I have long postulated that loose bearings and overly thick gaskets, that result in excessive play at the hub end, result in the half shaft breaking at the diff end.


This thread was discussed between 21/07/2021 and 27/07/2021

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