Just to cover myself I have been asking locally for firms to balance the crank. One has come back with a quote for £105+ vat. I need to tell them what the balance factor is, so opening a can of worms here what is the factor for a BSA A7 pre-unit crank standard road going??. The firm I enquired with is Julian Godfrey at Heathfield,Sussex anybody used them?.
I will be popping into a more local to me firm Goodland engineering but I am not holding my breath they seem to dislike small jobs. I will continue to hunt the issue but when its ticking over first thing in the morning and in neutral,the bike shakes and I would say that rules out the box?. As it warms up the shakes/vibration are improved and it is happyist at 45-50 mph. But push it up the rev range and the vibration returns.
If the crank needs a re-balance what would push it out of balance as I have owned this bike for 20+ years so its not unknown history to me. This is its third crank as the first was just worn out,the second balanced by fred cooper and broken by me,the third from Yeomans over ten years ago.
Andy