Is this a magnesium / mag alloy diff casing?

[Matt Elan]

Afternoon folk
Just got back from picking up a couple of cranks and the guy i'd bought them from asked me if I knew if the diff casing (see pics) was a mag alloy one? It was 1/2 - 2/3rds the weight of a normal alloy one, and had the extra number M 40139 cast in below the standard Lotus part no. It also had four extra lugs inside, presumably for an LSD. Any ideas what he has?

Pic 1: outside

Pic 2 - inside - LSD lugs?

Pic 2 - Additional cast in number

Looking forward to hearing your views!

[nmauduit]

aluminum density ~2.7 magnesium density ~1.7, plus the darker Grey color (natural oxidation) speaks for magnesium... a bit of added lightness for a racer, though not a lot compared to the stock version (is it for sale?)

[promotor]

The lugs inside look to be there to allow as much material in the casing while making (minimal) room for the 4 differential main cap bolt heads. They can't be to hold anything as you wouldn't be able to get to them once the diff pig's head is installed.

Looks a nicely made thing, probably really only any good for an out-and-out racer.

[vstibbard]

Looks like my 26R ones, same casting material difference only, back dichromate coating etc

V

[nmauduit]

Looks like my 26R ones, same casting material difference only, back dichromate coating etc

V

one can note small casting differences with some similar parts currently being offered (though I don't know if there have been variations along the years) - no affiliation on my part



https://www.tonythompsonracing.co.uk/pa ... -26r-spec/