Hello everyone,

I’m trying to change the top end on my bike but I am not sure on what size piston I should get? I measured the bore size and I got 71.3. Also how much clearance am I supposed to leave for the piston?

Thank you all in advance.

Yamaha always ran 70mm piston [except for maybe very late "80's experimenting with smaller bore & long stroke]. So now there's a problem As 71.3 is unlikely to be Yamaha max of 71 plus worn 12 thou. Not sure what to say next--you might need to go aftermarket like wiseco [or something better] & bore it to 71.5 although its not far from there now. What's on top of the old piston, wiseco numbers or just yamaha 1.0 stamping. Wiseco go in half mm steps 0.50, but yamaha go in 0.25mm steps but only to 1mm over. I'm woffling & confusing myself lol.

What is used to measure bore?

cliff