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MG Midget and Sprite Technical - Half shafts

My Mk2 Sprite has the original half shafts part number 2A7085, these have weaker material than the later BTA806 part numbers that use EN17.
I have a set of the later ones so thinking of fitting these.
However I also have a set of shafts taken from a spare axle I bought years ago. These shafts are one 2A7085 and one BTA806. What confuses me is that both of these have EN17 marked on the end - see picture. Where some of the later 2A7085 shafts made from EN17? This 2A7085 however does not have a groove machined on the end of the spline like the BTA806 shafts.
Les


Les Robinson

Thought I would check mine. I believe they are the original for my MK1 Sprite. There is some sort of lettering in places on mine, but barely discernable. Even assuming they should be 2A7085 it takes a good deal of imagination to match the markings to that number.

No help to you though. Other than yours show the lettering in a much higher relief than my (originals?) suggesting perhaps yours may have been replaced with ones of later or aftermarket manufacture?
GuyW

While you have them out I would suggest crack checking all of them, easy to do with a die penetrant kit. When I became aware of the cracking issue I pulled my halfshafts and I could visually see they were cracked with a naked eye as they were that bad but did the die penetrant check anyway to see what they looked like. Do both the spline and the mushroom end, particularly the inside, as the only failure I've had was at that end and as I understand it that's unusual for a road car, not so much for a race car. The crack at the outer end was probably due to the rough machining where it transitions from the shaft to the flange.
David Billington

Guy
Here is picture of my originals as still fitted to the car, probably same as yours. It’s hard to read the numbers but can make out part number.
Les

Les Robinson

David, good idea to crack detect.
I have been reading up on assembling the half shafts and apparently the gasket thickness is important. The height of the bearing outer race to the hub surface is measured and the gasket should be 0.002” less than this. The original gaskets were 0.006” thick and should be used like shims to get correct height. Some of the thicker ones that are sold can be too thick resulting in the bearing not being clamped properly. At least that’s my understanding.
Les
Les Robinson

Look up Malcolm Le Chevalier: he sells a useful rear wheel bearing kit that helpfully includes a selection of gaskets at different thicknesses. I am unsure if he sells the gaskets seperately
He also produces a triangulation kit for the front suspension that one of my Spridgeteer Group (ex Kent Masc) acquaintances has fitted.
Alan Anstead

I believe that there was also another halfshaft produced in between those two - BTA501.

I don’t think I’ve seen an early version with EN17 on it.

Does anyone know why the later halfshaft has a groove?
Dave O'Neill 2

Not been on here in months - seems good timing for me to come back and check in!

Les is correct in his understanding. Search on the topic and you will likely find my research and ramblings on it, but Les sums it up nicely.

I can still do the gaskets if ones being supplied are still out of spec. Ideally they should be 0.4mm thick, or less. If they are thicker than 0.4mm (before installation), bin them!

Had a few dealings with cracked half shafts too. But that's always going to happen with 110hp, fatter tyres and track/sprint driving.

Hope you are all keeping well.

Cheers,
Malc.


Malcolm

Dave
yes BTA501 was fitted to 1098cc Spridgets up to the introduction of the BTA806 ones. Of course any BTA940's are the ultimate. I thought I had 2 NOS ones somewhere but recent searching has revealed only a new BTA 806 :(
Bob Beaumont

Dave,
(Does anyone know why the later halfshaft has a groove?)

Perhaps the groove was just to identify the shaft as being EN17 prior to the end cap, marked with the part number and EN17, being fitted.

Simon
S Holt

The 2A7085 shaft that I have which is marked EN17 has no groove!
Les
Les Robinson

Ah, good point Les, I forgot to re-read your original post before making the suggestion!
Maybe they decided to change the material to EN17 and made some using the original part number, then decided to change the part number to denote the new material and added the groove as an identifier.
Simon
S Holt

Simon
You might be right, I was thinking the same.
Les
Les Robinson

This thread was discussed between 04/01/2025 and 05/01/2025

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