Does anybody know if the top end off a Express 300 aircooled would fit a 250 TB bottom end? I think the rod is the same so the piston would fit but will the head bolt up to the 250?

Thanks
Greg

 

Greg,
It may fit but it won't work. The stroke is 60mm on the 250 and 65 on the 300. Your deck height would be wrong, your ports would be in the wrong location which would mess up your timing. You could have somebody who knew what they were doing bore your 250 for a 300 piston and then he would still have to fix the port timing and deck height for proper operation. It would get expensive and you would only go from 244cc to 261cc. You can get 258cc with Wiseco's largest overbore for the 250.