Front Wheels Bearings - with a twist

[IslipMinor]

The hubs on our Minor are from a disc-braked Midget, but other than that they use the same bearings, spacer and oil seal as the Minor.

Some while ago I replaced all the bearings with the correct 'face adjusted' ones, but even so the RH hub has had a bit of free play that has got slightly worse over time. It still passes the MOT, but it was not going to get any better. So I either had to get a replacement hub, which might not be any better and would need machining to provide the caliper clearance, or find another solution.

Our elder son has an MGB and the front hubs and bearings are unusual in that it uses taper roller bearings, but with the inner races clamped against a spacer in a very similar way to the Minor, except that it uses shims to provide adjustment to achieve the required end float.

Last week I bought a selection of shims for an MGB hub, and today I took the RH hub apart and machined 0.010" off the spacer's length - not very easy on a lathe as the two faces must be parallel within very close limits, and the spacer is a largely unmachined casting. Easy with a surface grinder, except that I don't have one!

Once done, I reassembled the hub with the reduced length spacer and a 0.005" MGB shim to see whether I was in the right area, and as luck would have it, it was perfect. Smooth running and no free play.

All very straightforward with one exception. The shim fits between the outer bearing and the spacer, and until the castellated nut is tightened, there is a small gap, so it has to be held in place with grease. The first one moved as I slid the hub on to the stub axle, and the shim caught in the thread and damaged it. The second attempt worked fine.

So often we hear about fitting new bearings and still having too much free play, which could well be the result of using non 'face adjusted' bearings, but the newest Minor front hub is 40+ years old, and very like showing some signs of wear on the faces at the ends of the bearing bores. Reducing the spacer length and using shims provides a way of taking up that wear, but retaining the designed bearing pre-load.

It also introduces the possibility of using taper roller bearings - the spacer would need reducing much more as the taper roller bearings are wider. It would retain the clamped inner races that provide strengthening to the axle stub, which for me is very comforting, and why I have not gone that route yet. With taper roller bearings the inner race of the outer bearing is assembled at the end, so the shim can be put in place over the stub axle with no risk of damage. Might have a look at that next.

[bmcecosse]

I believe there are taper roller bearings for the Minor hub Richard - it's been mentioned before. The MGB bearing system is very normal - by far the way I like my taper rollers ! The Mini bearings (where taper roller) have always been that system - clamped on a central spacer with the hub nut done up TIGHT. My TR7 has the 'loose' bearings (I suspect the hub is same as Marina) where the nut is only lightly tightened and held with the split pin. I don't like it! But at least last year when they 'advised' a little play in one hub - I only had to move the nut round one flat - and fit a new split pin.....

[philthehill]

You use the term 'Face adjusted bearings'. I have done a search and can only find it re your post above.
Can you please explain what you mean? I think I know what you mean but could you please clarify.
I have fitted hub bearings in both sprite/midget & Minor and never had any problem or had to source 'Face adjusted bearings'. But there again the hubs were not worn (laterally I presume).
I have now found the following link with info on the web:

http://www.mgexperiance.net/article/mg- ... rings.htlm

Reading the article it looks as if the use of 'Face adjusted bearings' has come about because of the demise of the original 'fit and forget' specification bearings.

[IslipMinor]

'Face adjusted' refers to the tolerances that the whole bearing assembly is built to, and is the original bearing specification that BMC used for the Minor, A30/35/40, Midget and Sprite front hubs. When the hub is fitted on to the stub axle and the castle nut tightened, the hub/spacer/bearing assembly is designed to pre-load the bearings and there should be no free play at all.

Equally there must not be too much preload either, and achieving this in a regular production environment means that the hub inner shoulders, spacer and bearings all have to be manufactured to very close tolerances.

The overall width of an angular contact bearing is the result of a build-up of the dimensions and tolerances of the two races and the balls, and could be the least consistent of the three hub parts, hence the need to use 'face adjusted' bearings, which are manufactured to a very close overall width tolerance.

Of the two Midget front hubs we have, one has never had any free play, with or without face adjusted bearings, but the RH one had been a bit marginal for a while now. I will keep an eye out at Beaulieu this year for a spare hub.

Roy, Yes there are taper roller bearings with the same inner and outer diameters(inner part number is 30205 and outer is 30303), but they are both wider than the standard angular contact bearings. Without detailed dimensions I don't know whether it means that the spacer will need to be shorter or longer, or the same, and if the inner bearing inner race is a different width, that could affect the alignment of the caliper and the disc.

[bmcecosse]

I believe they are a straight replacement fit - but probably with the 'loose' nut and split pin - no inner spacer.

[philthehill]

Islipminor
Thanks for clarifying the term 'Face Adjusted Bearings'. Perhaps I have been lucky and never had to source or use bearings other than original spec supplied from BMC/B/L.
I have Marina stubs fitted to my minor with standard spec taper roller bearings so very easy to take up any excess play.
In your post above you refer to keeping the spacer if you change to taper bearings. I cannot see your reasoning for keeping the spacer. It will not increase the shear/load strength of the stub axle even if you 'fit' the spacer so that the bearing races against the stub axle are locked and the free play of the bearings is mechanicaly held. The only benefit to be gained as far as I can see is that the hub nut can be tightened solid (perhaps that is what you are aiming for) and not loose as on a Marina set up where the nut is only held from rotating by the split pin/split pin collar. But as of yet I am not aware of any failure with the Marina hub nut retention method. Perhaps I am missing a trick here; if I am please let me know. To overcome any increase in the shear or overloading of the Minor stub axle is the reason why I fitted Marina ones.

[IslipMinor]

The clamped bearing and spacer adds strength to the complete Minor stub axle/bearing assembly, which is why, if I were to go the taper roller route, I would use a 'clamped with shims' arrangement. At the moment, if my slightly shorter spacer + shim gives me a long-term solution, I shall stick with that. I know of no failures first hand, but have read reports of them on Midgets/Sprites.

I will still look out for a Midget steel wheel disc braked hub, at a sensible, not current eBay, price, as a spare!

If the stub axle had been designed for the 'nip it up and back it off' split pin arrangement to give a small amount of end float, I would not change it, i.e. Marina and many other rear wheel drive cars.

[philthehill]

I still do not see how you can add strength to the stub axle with the solution you describe! The stub axle is the only part that the wheel, hub and bearings relies on to hold it together; not the bearings or bearing spacer sleeve however arranged. It does not make the stub axle diameter any larger and it is diameter that counts. Anyway I am happy to agree to a disagreement on this matter.

[bmcecosse]

I have to say I agree with Phil - it can't possibly add any strength. Nevertheless - the 'clamped up tight' is by far the one I prefer - but probably just because it's what I was used to with my Minis.

[IslipMinor]

The clamped up bearings and sleeve do exactly that - increase the effective diameter of the stub axle by creating a compound member. Obviously the ultimate strength is not just the stub axle, but strengthening it will move the weakest link somewhere else.

[bmcecosse]

Can't see it - you are clamping on the original stub axle....and it's under greatest strain where it leaves the fixing in the kingpin. That doesn't change. But it matters not, since stub axle failurs are unknown.

[IslipMinor]

The greatest bending moment is at the exit from the upright, but the diameter is much greater there. The diameter where the inner bearing fits is much smaller and will see greater stresses, which is what causes ultimate failure. If it didn't need reinforcing, the original design would not have incorporated it - that seems well founded information that I am happy to continue to adopt.

[bmcecosse]

Have any ever been known to fail??

[IslipMinor]

I'd rather not experiment to find out! Weakening and then subjecting it to greater than standard loads and stresses does not seem like a good idea to me.

[bmcecosse]

I don't think anyone is suggesting any 'weakening' ???

[IslipMinor]

Removing the clamped spacer weakens the overall stub axle assembly.

[bmcecosse]

I do see what you are getting at Richard - but I'm not convinced a clamped assembly like that adds any significant strength to the solid stub axle.

[philthehill]

Islipminor
To clarify a point you have made above. I have the Minor stub axles removed from my uprights in front of me as I write this post and unless you have modified the stub axle the Minor stub axle does not have a reduced diameter for the inner bearing. The diameter of the stub axle on which the inner bearing sits is the same diameter as that part of the stub axle fitted into the upright. Yes the outer part of the stub axle (next to the hub nut thread) is reduced to suit the outer bearing. Whilst I have no evidence to disprove your theory as to why the solid spacer was fitted I consider that it has more to do with the fitting of the angular contact bearings from car No: 228267. Ref: Minor Wksp Man sect K7.

[IslipMinor]

The stub axle is a cantilever supported by the upright. The stress profile along the length of the axle would be very progressive if the axle section remained constant, or slowly changing, but it isn't. The shoulder butting up against the upright and the diameter for the oil seal is 35mm, but then reduces suddenly down to 25mm for the inner bearing. The sudden section change causes a stress concentration in the corner, which is why there is a small radius to reduce the effect a little.

Having the bearings and spacer clamped up against the shoulder created by the section change, increases the effective section area of the stub axle, reduces deflection and the associated stresses.

A similar situation exists for the end of the stub axle going into the upright. Here it is pressed into the upright up to the shoulder, which again adds significantly to the strength of the assembly. It is exactly the same principle for both ends of the stub axle.

BMC could have used conventional twin taper roller bearings, adjust for end float with a 'loose' nut secured with a split pin, but choose to go the more expensive pre-loaded and clamped angular contact bearing route. This needed close tolerance manufacture on the inner shoulders of the hub and the spacer length/parallelism, neither of which are required with conventional taper roller application. They must have believed it was necessary.

On the subject of stress concentration, did anyone watch the C4 programme on Sunday night about the early 'unexplained' crashes of the Comet airliner? After much research and testing, they found that the square windows caused stress concentrations in the corners, which created small cracks that then propagated and resulted in a total, sudden airframe failure. Ignore them at your peril!

[bmcecosse]

I missed that Comet prog - but I did know about the square window problem.... I'm old enough to remember the Comet explosions on the news....