classic motorcycle forum

Motorcycle Discussions => British Bikes => Topic started by: wetdog on June 06, 2013, 03:21:29 PM

Title: bsa b31/33 barrel id
Post by: wetdog on June 06, 2013, 03:21:29 PM

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

Title: Re: bsa b31/33 barrel id
Post by: john.k on June 07, 2013, 01:55:19 PM

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.

Title: Re: bsa b31/33 barrel id
Post by: wetdog on June 07, 2013, 03:49:38 PM

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

Title: Re: bsa b31/33 barrel id
Post by: wetdog on June 07, 2013, 04:51:07 PM

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