xs 650 engine mods

hi there ive heard a rumour that the xs 650 u.s motor cant be tweeked i.e bored and made bigger can anyone shed any light on the subject is this rumour a load of crap ? Ive been told u.k engine is the one to get

Hi Graham

From what I remember some US motors used a shorter con rod, therefore the piston was higher from pin to crown. The pistons used for big bore are not as high which will result in very low compression.
However I have used these motors when stroking the crank and in effect returning to original piston pin height. Saves machining so much from piston crown or as some people do, using a spacer under barrels.

Hope this helps

Le Shepherd

hi thanks for the info im in the middle of building a u.s xs 650 powerd wasp the engine is standard is it worth trying to tweek the engine or would you leave it standard ? what sort of mods would you make ?

best bloke to ask is chris moss sidcar 29 he has loads of stuff and knows both us and uk engines inside and out

I have seen TT500 (880cc) pistons used on 447 (U.S short 130mm rod) engines, the cylinder block had bee reduced in height by about 10mm to allow for the shorter rods. Cam chain would have to be shortened, new head mount made, and the underside of the pistons may have to be machined to allow piston/crankshaft clearance.
I have an 850cc using the 447 (U.S) rods, I use Ross pistons that Dave rayner in Australia used to stock, but I don't think he has any more.
I can get the drawings of these pistons if anyone needs some made, minimum order of 4 from Ross, I don't know how much they would cost.

Cheers,
Matt.