Update- thanks for everyone who replied. I rotated the crank a few times and looked for marks or any indication something was hitting. Nothing... Here and on another forum someone suggested that those were casting marks from the original manufacturing. I went ahead an put the new wiseco piston in and all is good. I haven't rode the bike yet, just let it idle for a few minutes to get a heat cycle on it. I can say that it idles much smoother than before and unless it's my imagination, the motor sounds a tad bit less noisy. Anyways, thanks for the input. If the bike grenades itself on the first ride, I'll let y'all know.
I recently did my first top end job on my 2012 KX450. Nothing was wrong, I bought the bike used with unknown hours and wanted to start fresh. The cylinder looked great and so did the piston. Well, on the bottom of the piston I noticed 4 places where it looked like there was some sort of contact. You can see where the aluminum was being "tapped". Has anyone seen this before? Like I said, the bike runs fine and isn't noisy. I am about to install a new Wiseco piston. Should I be concerned this will happen to it, also? I have attached pictures. Thanks, Chipper