Lotus Elan

Is this a magnesium / mag alloy diff casing?

PostPost by: Matt Elan » Thu Mar 08, 2018 5:11 pm

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?


img_1539-2.jpg and
Pic 1: outside



img_1538-2.jpg and
Pic 2 - inside - LSD lugs?


img_1537-2.jpg and
Pic 2 - Additional cast in number


Looking forward to hearing your views!
Matthew Vale - Classic Motoring Author
1968 Plus 2 - Somewhat cosmetically and mechanically modified
1969 Plus 2S - Currently undergoing nut and bolt restoration
Visit me on matthewvale.com
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PostPost by: nmauduit » Thu Mar 08, 2018 5:25 pm

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?)
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PostPost by: promotor » Thu Mar 08, 2018 5:47 pm

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.
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PostPost by: vstibbard » Fri Mar 09, 2018 5:43 am

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

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PostPost by: nmauduit » Fri Mar 09, 2018 9:55 am

vstibbard wrote: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

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