Yes and no...They will fit but the footrest arrangement on that side has to be altered as it goes through the cases on the steel variant but not with the aluminium ones....
You may also have to slot the three holes that the bolts pass though to retain the inner case...
A slight alteration to the chain guard mounting is also needed to tie it to the inner case at the front of the chain guard...
It requires a bit of fiddling here and there but nothing to technical...The biggest job is the footrest...
I ran alloy cases on my rigid 1951 B33 for years...Ian
OK, so what model BSA chain case will fit? I am guessing it needs to be from a swing arm B model or did rigid or plunger models ever have an alloy primary?
The modifications for the foot rest do not seem to be much of an issue.
Ideally you need an inner and outer case from a magneto swinging arm B31/33..However, these suit the Goldie (there are only minor differences) so good pairs are fetching £250 or thereabouts....
The outer is common to a swinging arm A10 so these can be found quite easily and at a reasonable cost...There are early and late types, the earlier type is cheaper generally, the late type more practical...
Plungers had the inner case cast as part of the crankcase and the outer is much shorter due to its 'semi unit' construction, with the gearbox bolted directly to the back of the engine...So, not suitable..
You can use an A10 inner casing with some modification...You'll need access to a lathe and some other workshop equipment and also alloy welding facilities....The job itself is not overly complicated...The payoff here is that A10 inners are common and cheap....Ian
