BSA C15 piston swop

[davet147]

Hi everyone, can someone advise please.

I am in the process of restoring my C15 1960 and didn’t want to put the existing head on as there was a few fins broken. I have got my hands on another piston and matching barrel from a chap, the only thing is it is a SS80 piston with marks 30.4764 and 40-642 BSA 1mm OS. The chap tells me I can put it straight on no issues. Can someone please reassure me this is the case as I am a little apprehensive and need some reassuring. I have gone through my Rupert ratio's book and it does mention 40-642 as a +040 with a Comp. ratio of 8.75:1. The other issue I have is there are no defining marks telling me which is the front as fitted.

Thanks Dave.

[Goldy]

I think that you will find that it fits ok but the thing that would concern me would be the higher compression ratio. The weakest part of the 1960 C15 is the big end if its the original small diameter you might have problems.

[twolitre]

1mm is O.03937inch (otherwise 2/3 of a thou short of 40 thou)

[davet147]

I think that you will find that it fits ok but the thing that would concern me would be the higher compression ratio. The weakest part of the 1960 C15 is the big end if its the original small diameter you might have problems.

Thanks for this. I am about to split the the engine, what would be recomended to install for the big end? Should I just look at a upgrade?

Thanks.