I need piston advice for my top end rebuild

[confusedyouth]

Hi, I’m about to do the first top end on my 2001 YZ80, this is my first bike but I am very experienced on cars. I just got the bike a few months ago from the second owner, who says he thinks the piston is original. So with error on the side of caution I’ve decided to put a new piston, ring, wrist pin and wrist pin bearing in the bike now my question is should I get a standard bore piston which I assume is 47mm (the spec according to the service manual is 46.9 something mm) or should I go bigger and if so how big? And after I do the top end what should I do to break the new piston in? (I’m going to get a forged Wiseco piston) Thanks in Advance.

 

[RM_guy]

The cylinder is plated and lasts a very long time so there typically isn't any need for oversized pistons for normal rebuilds. If the plating is worn or flaking off then get it replated. Go with the std size and read this thread http://dirtrider.net/forums3/showthread.php?t=42210 for info on prepping the cylinder.

Weisco is a good piston choice but it must be broken in carefully with several heating and cooling cycles. Here’s a couple of good threads:
http://dirtrider.net/forums3/showthread.php?s=&threadid=35945
http://www.dirtrider.net/forums3/showthread.php?t=40915

 

[bikepilot]

Great info above. I'll add that if you want you can pull the cylinder off and mic it. Pro-X offers pistons in minutely different sizes to account for production variations or cylinder wear.

good luck