bsa b31/33 barrel id

[wetdog]

been offerd a b31 engine (which I need project) owner says the top end is 500cc but is not willing to remove the head , I know there is a way of telling the b31 barrel from the b33 but im f***ed if I can remember how (old age) can anyone refresh my memory . thanks

[john.k]

There s a 14mm diff in the bores,so it s not hard to tell .If theres a lot of space between the studs and the casting,its a 350.Incidentally the 350 barrel can only be rebored safely  to give around 410 cc s,so don't fall for that story.Regards John.

[wetdog]

"space between the studs and the casting," ........ any idea of a distance ? thanks

[wetdog]

remember now , little finger behind stud equals 350cc , thanks its a 500 so will collect