G'day Dennis . My Can Am Sonic is still on standard bore , as the motor has never been apart , but it is getting a bit low on compression . I have a spare piston from an ATK 604 that I would like to use . I probably could just use another sleeve , just as long as I don't have to bore the cylinder muff out to fit it . I also have a spare cylinder head from another Sonic and so wouldn't mind having a complete spare top end .