Hi,I have recently bought a TY250 mono as an introduction into motorcycle trials, I decided to rebuild the bike from scratch and upon stripping the engine it has thrown up some interesting modifications which I hope someone could enlighten me on. The piston is I've been told is an IT 175 at 66.5mm diameter, the rod is different, Its a 214 but possibly same length as standard. The barrel is 10mm shorter than standard and the crank throw is shorter at around 63.5 in length. There seems to be quite a decent porting job in the barrel as well. It also has a lightened flywheel. The frame no is 15. Someone told me this is an early conversion by John Shirt to build a more revvy motor,but I really dont know,any help ideas appreciated.

Thanks regards Dave.

Edited May 27, 200818 yr by Stickymint

mick andrews did a lot of work like this on ty yamahas i wonder if its one of them.

Thanks for that,anybody know if he's contactable for information. Ta.