How can I find engine specs , is there any good books with it in ? What are the standard size of large journal crank big ends please .
What year? Cranks don't have big ends, con rods do. Probably 1.8435"
A real good book would be the BSA manual. Google it.
If you go into the Members Section on the website you can download service sheets. Sheet 702 gives info on crankshaft dimensions which may be of some help to you
I would think, cant remember!!, Roy Bacon's book on the BSA twin should have a lot of information as would the haynes and BSA own manuals. the factory manual would probably be best