I'm in the process of rebuilding the top end on my Banshee, the top of the pistons have 1.00mm stamped on them. It seems like I've heard that is .40 over stock size. Just to ease my mind I was wandering if anybody knew. I'm hoping so, that way I can just go .20 more with a Wiseco setup. Thanks Dennis

 

Look up Wiseco's website. Their books show the sizes in detail for each model. Is that Yamaha brand piston? If not that 1.0 could mean it is bored 100 thousandths over already. Too big for a .020 over. Wiseco may have bigger or you may be looking at new cylinder sleeves. They are also available from Wiseco for most models. Wiseco also has catalogs with all the data, very good to have so you may request one.

 

You are right that 1mm = .039"