b31 light wieght gearbox

[MAD99MIKE]

 I understand that there has been some info on fitting the later plunger gearbox into xb and yb31 frames can any one help with info dimensions or parts needed thanks for any info forthcoming.

[idie]

I believe the lugs need thinning on the later box

[Derek996]

The information you need is in this thread. [url]https://www.bsaownersclub.co.uk/bsaoc_forum/index.php?topic=12813.msg68583#msg68583/url
I saved it because I too have a lightweight box in my B32 and might need to convert one some day.
When I was at the Belgian Classic TT  in Gedinne a be few years ago I saw some very tuned rigid framed BSAs with what appeared to swinging arm gearboxes but I later realised that they were probably the later 4 speed C11G gearboxes. Might be another option but won't look original.

[MAD99MIKE]

thanks for both replies will look at reducing width on later plunger box