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MG Midget and Sprite Technical - Halfshaft identification

My mk2 Sprite has the old 2A7085 part number halfshafts.
I have some of the later ones, BTA806, which I am planning to fit. However some have EN17 marked on the end but some don’t. All have the groove at the spline end.
Are all BTA806 made from EN17? Why do some have it marked on and some don’t?
Nothing is ever straight forward!!
Les
Les Robinson

As far as I know BTA806 were all EN17.

I have a selection as well and some have EN17 and some don't, equally some have the groove in the end and some don't. This includdes a NOS one still in its wrapping!
Bob Beaumont

On the assumption that all BTA806 are EN17 then I’m going to replace my original 2A7085.
Just crack detecting the BTA806 spares that I have.
Les Robinson

Or do I leave originals in? This is doing my head in. Am I worrying about nothing.
Driving to Germany end of next week for a Black Forrest tour and then Treffen .
Been Germany and France loads of times, even blasting round Zandvoort circuit in Holland and never had an issue.
Les Robinson

They can crack quite a bit before actually failing IME, it depends how you drive. When I first heard of the problem I pulled the halfshafts out of my frogeye and the cracks were clearly visible with the naked eye so it was a matter of time to failure. I crack checked them with dye penetrant just to see what it looked like, lots of pink/red lines in the white dust coat, and they got replaced with later stronger shafts. One of those later failed at the outer end likely due to wide tyres and probably stress concentrations due to the rough machining inside the mushroom at the outer end of the shaft. Growlerising could include cleaning up that area to improve the finish if it doesn't already.
David Billington

Crack detecting done, all good.
Have one pair of shafts which are marked RH and LH, however both shafts have quite heavy wear on both sides of the splines, guess it’s possible they have changed sides at sometime in the past.
Another set is not marked LH and RH and it’s not too obvious which is which, spline wear not bad on these. Think I might take a guess on which is which and go with these. These are the ones marked BTA806 but no EN17 marking.
Les Robinson

I had 3 shafts break in my midget.
Every time took everything out of the axcle flushed out metal bits with diesel and buitlt it back in.
I then didnt know about keeping a left one on the left side, I just randomly put back in shafts :)

This may have speeded up the next ones breaking...
Wisdom come with age LOL







A de Best

Don’t know what to do now, change them or not. I’m thinking “if it ain’t broke then don’t fix it”.
With my BTA806 shafts I can’t say with 100% certainty which is LH and RH.
What ever I do will be the wrong decision!
Off to Germany this weekend, finishing at the Treffen.
Thinking might keep my 2A7085 shafts and take a spare set of shafts with me, but then again might change them. This is doing my head in, driving me nuts.
Les Robinson

We have been with you on the continent many times since 2014 and I have always carried 1 driveshaft "just in case". I wrapped it in cloth secured with tie wraps to stop it marking the luggage. Guess what Les, I still have it, still wrapped in cloth and still in the back of the Frogeye.

Whether a spare driveshaft works like a rabbits foot or not, I don't know (but it didn't do the rabbit much good).

The likely hood of breaking a driveshaft is tiny and the likely hood of breaking 2 is miniscule.
If you are a little weary why not take 1 left and someone else take 1 right driveshaft.
Rob
MG Moneypit

Thanks Rob
My current plan is to keep existing shafts and as you suggest take a spare although in another 5 minutes might change my mind!!
Les
Les Robinson

One final question:-
Is oil 80W-90 GL4 ok for axle/diff?
Les Robinson

EP90

https://www.opieoils.co.uk/p-77274-castrol-classic-ep90-mineral-based-multi-purpose-extreme-pressure-oil.aspx
Dave O'Neill 2

Cheaper at Demon Tweeks.

https://www.demon-tweeks.com/uk/castrol-classic-ep90-gear-oil-cas1840/

Rob
MG Moneypit

Not with VAT.

Also, Opie Oils usually have a 15% discount offer.

It could be cheaper at other suppliers. That was just an example from a quick google search.
Dave O'Neill 2

O-ring that goes between hub and half shaft, any idea what dia the cross section is. I have some from 2 different suppliers and they are not the same, one is 2.5mm and one is 2 mm.
Les Robinson

O- rings are 3mm and 3.5mm not 2 and 2.5 - think need to go Specsavers!!
Groove depth measures 2.6mm so either O-ring should do.
That’s it now, no more farting about and worrying.
Les Robinson

I’ve just measured this one at 2.9mm

It was 2.99 including the bag, which measures 0.09mm.

EDIT: In that case, use the 3mm.


Dave O'Neill 2

It would be nice to know the original specification as it might be an inch BS O ring. What are the dimensions of the groove it sits in?. OD ID depth. Not that a metric one won't do the job, the bearing is after all metric, the O ring may not be.
David Billington

I’m hoping the Rover one is to original spec, although I can’t guarantee it.

It’s from the early ‘90s.
Dave O'Neill 2

According to engineering standards, for a 3mm O-ring the groove depth should be 2.45mm. For a 3.5mm O-ring the groove depth should be 2.65mm. This is to withstand a pressure of upto 100bar, hopefully the rear axle won’t be anywhere near that!!
Les Robinson

IIRC the Parker O ring handbook is one of the standard reference sources for O ring design and is/was available online. O rings are or can be a complicated subject and it depends on whether it's a static or dynamic seal and the pressures involved. I would say this is a static seal and not subject to any real pressure, I'm trying to think what the axle would look like at 100bar.

I'm reminded I contacted Walther UK some years back about a propane quick connect and the technical guy said it's a non aggressive gas so one of their low pressure range would do the job, up to 100bar, I had to wonder what their higher pressure connectors were rated for.
David Billington

Long time no see, hope all are doing well.

It's been a while since I did the measurements and research into all this, so I forget the details... but I came to the conclusion that is was a BS 234 o-ring.

75.8mm bore x 3.53mm section.
Malcolm

Have just found another set of old hubs that I didn’t know I had!
O-ring is 3mm

Anyway that’s it now, guess either a 3mm or 3.5mm will do.

So moving onto next problem - see headlight topic.
Les Robinson

This thread was discussed between 30/05/2025 and 04/06/2025

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.