Since my little chance meeting with a post at the Hanbury scramble I have a fair bit of spare time on my hands at the weekend, and no, this does not mean spending quality time with the wife christmas shopping.

Was thinking about putting a BSA unit into a Bultaco or Fantic frame, so has anyone got any tips or pointers as to the best direction to take?

Does anyone have any photos of similar projects?

I simply want a build a cheap (ish) bike and ride in local trials, so not worried at all about eligibility etc for the flag ship events.

If anyone has done this before and I'm sure people have, what makes the best combination in terms of frame and engine?

Thanks in advance.

Edited December 3, 201213 yr by wallo

Should be possible - what sort of BSA unit? Back in the period a chap up this way fitted a Triumph twin in to a "blue" Bulto. It always seemed a bit top heavy to me but didn't half go. Mind, his road bike was a BSA frame with a Saab motor in it.

Get on and have a go - a mate of mine put an XL250 engine into a small wheel KX80 frame.... Lots of cutting and welding,but was great fun around the farm ! As long as you dont lose the basic geometry of the frame I cant see that it matters too much.Obviously a unit Beezer motor is going to be heavier than a 200 Fanny - but its for fun,so it wont matter.

Must get around to finishing my TY/Serow project,drinking less on a monday night might help.

Hadn't really thought about putting a more modern engine in it, but worth a think. Does anyone know the hieght of a C15 or B40 engine, I think I have around 16 inchs in the Bultaco frame I was looking at?

About 20 yrs ago I put a 500 triumph in a Bultaco frame by cutting out the bottom tubes and dropping the farme over the engine, it lost a bit of ground clearance, it didn't steer properly, and was pretty useless as a trials bike. I had kept the original Bultaco geometry but the weight distribution was all wrong, too heavy on the front end. I then made my own frame around the engine and it now works quite well. 2 stroke frames and 4 stroke engines aren't generally compatible, the top frame tube from the steering head to the seat is usually too low on a 2 stroke to fit the taller 4 stroke engine, unless of course you drop the engine so that you have very little ground clearance. Be prepared to do a lot of cutting and welding around the main frame loop in order to fit the engine and oil tank. By the time you have finished you will probably find the only thing left from the original frame is the steering head, swinging arm, and a bit of the subframe. A small engine such as a Cub or 125 Honda may be possible with less modifications.