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MG Midget and Sprite Technical - Current rear wheel bearing codes

At present I'm preparing my 1275 Sprite for a dare from a 'mate' to join him at a track day.

Among other things I decided that a pair of uprated halfshafts would be a good idea, but they in combination with Revolution wheels have necessitated a last minute job of fitting extended wheel studs. I've got the hubs off, because the longer studs won't feed through in situ. I decided that I'd better replace the hub oil seals, which in turn suggested new wheel bearings.

The ones that have come off are R&M LJ35. The modern code would appear to be 6207's (72 x 35 x 17mm).
But what tolerance should I ask for? 000?

I'm hoping to get a pair from my local bearing factor tomorrow rather than order some and twiddle my thumbs.

I really should have left well alone. No, I should have said no to the track day. I've just seen the list of attendees.

Mark
M Crossley

Mark,

The rear wheel bearings are nothing special. 6207 will do you just fine. The trick is in the rear hub gasket thickness.

The rear bearing sits something like 0.01" proud of the rear hub (assuming your hubs are not worn) and should be clamped between the hub and the half shaft by selecting an appropriate thickness gasket that acts as a shim.

Take a look at the attached hub/half shaft that I assembled together with a gasket from a commonly available kit. I cut a section out of the gasket in order to be able to slide the feeler gauge in. There is a 0.015"+ gap between the bearing and the half shaft. The gasket is way too thick.

To this end I have drawn up and CNC cut my own rear hub gaskets of varying thicknesses to ensure the correct shimming of the rear hub bearing. I have made this into a kit that you can find on a popular internet auction site :-)

Give me a shout on malcolmlechevalier at gmail.com if you want to know more.

Cheers,
Malcolm

Malcolm Le Chevalier

Another shot showing how the bearing sits slightly proud of the hub. I measured this as 0.01" for this hub. The gasket, once compressed, should equal 0.01". The big brand kit gasket is, I think, 0.03" (0.8 mm) uncompressed and compressed to 0.025", thus leaving a 0.015" gap between bearing and half shaft.

Cheers,
Malcolm

Malcolm Le Chevalier

Malcolm

You say that the bearings are nothing special, but I've had new bearings with more play in them than the ones I was replacing.

I have some NOS gaskets - I must get around to measuring them, when I get a minute.
Dave O'Neill 2

Hi Malcolm,
The selective assembly idea makes sense, and I've just spotted your kits on a certain auction site. CNC sounds great compared to scissors and a scalpel. I should probably stock up, although I hope I'll do the job right and not have to come back to it for quite a while.
I was wondering if I needed to specify a particular clearance for the bearings. I had the feeling that there were different grades of bearing C1, C2 C3 etc. The loose ones giving the worn impression that Dave mentions.
Dave, it sounds like racing wears the bearings quickly. How often would you expect to replace them? I presume sticky tyres and high cornering loads give a hard life.

Any ideas if I want anything other than standard grade/clearance?

Mark
M Crossley

Mark

Having snapped the end off a Peter May halfshaft due to a worn bearing, I was quite cautious and changed the bearings regularly, but wasn't that happy with many of the replacements.

To that end, I ordered a quantity of RHP bearings through a friend who had an account with a bearing supplier. I fitted the first pair and checked them on a regular basis over several seasons, but never needed to change them.
Dave O'Neill 2

Mark, back in the days of RHP we used to have three " fits" as you say. They were 1, 2 and 3 dot with 1 being the one with least clearance. I dont know what current manufacturers use to identify theirs. The dots were on one face and looked like a small circle, a sort of rub mark if the best way I can describe it. Too long ago now to remember so without looking at drawings I cant say if LJ35 and 6207 are identical but I would suggest not as we used to make both. Outside dimensions may be the same but they may have different size balls or internally have differnt dimensions.



Trev
Trevor Mason

When i replaced mine i used the double sealed, sealed for life type.

And no gasket, just hylomar red on the mating faces.

Its been ok so far, though it has to be said i dont do a lot of miles....
Andy Phillips (frankenfrog)

I have a couple of packs of original BL gaskets, they measure up at 0.020"
David Smith

Thanks David, interesting information. The kits I make have a range of thicknesses up to 20 thou. which from what measurements I have done should be sufficient. But it's nice to know this ties in with BLs original thinking.

What sort of material is it? Is it "typical" paper gasket material?

I ask as I have found different materials have a different compress-ability under load. It is my belief that not only are the gaskets in most kits too thick, but also too stiff (they don't squash that much), thus exacerbating the problem.

Cheers,
Malcolm
Malcolm Le Chevalier

more like very thin cardboard than paper so it looks like it will squash quite well.
David Smith

This thread was discussed between 29/06/2016 and 30/06/2016

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