unusual crankcase?

these crankcases have been on my shelf for a long time , and i have no idea where i got them from
the drive side is special (i think) in that it is sandcast
it also has got a weird number wich is not bodged . the case is machined to take a mk3 primary and has got very thick walls
there is also a bolt at the front fot i do not know what
does anybody know what it is?i don't

Any other numbers on it, ie casting number?

no ? no other numbers

that style of cases were abandoned early because owners had problems removing the cylinders as in pic (1)
or maybe they were development cases?

lynxnsu said:

these crankcases have been on my shelf for a long time , and i have no idea where i got them from
the drive side is special (i think) in that it is sandcast
it also has got a weird number wich is not bodged . the case is machined to take a mk3 primary and has got very thick walls
there is also a bolt at the front fot i do not know what
does anybody know what it is?i don't

Click to expand...

I think the number (850 - 012) is a prototype marking so likely to be original.

I think '79x100' might have mentioned those cases in a discussion we had some time ago as some 850 Mk3 cases have an unused boss in that location.
(photo - Bigbossmonty)



I think the plug/port in your crankcase was probably intended for checking crank position/ignition timing, however, the usual position for the Mk3 timing port is below the timing chest, so it seems they may have moved it to a more accessible location on production models unless your RH case also has the normal timing plug/port (below)?