BannedCR500Riders.com

I did a topend on my 250 a few weeks ago. Rod felt good up and down but a good amount of side to side, I was told this is ok? Just making sure.

Ok my real question. When going through this motor I was in a hurry and did it in a dimly lit area. I know better but it is what it is. But I finished, she started right up and I loaded her up to break her in the next day and jump her off some dirt humps. I rode for a while before I noticed she was running pretty chitty and was losing coolant. I hadnt cleaned the mating surface between the cylinder and the cases and coolant was leaking into my cylinder and out onto the ground. Busch leauge.

Pulled it back apart last night to do it correctly and my brand new piston had this gouge on it. The cylinder has no damage and it look great. What exactly would cause this? I zipped it back together but now I feel like I need to replace the piston ASAP. Im pretty bummed but I dont want to do any major damage because I am cheap. I am loaded up and wanting to do some riding today. Should I not ride it with the piston like this? There are no crack in the piston. Thanks in advance.

I would take some fine grit sandpaper and make sure there arent any high spots or rough spots along the mark BEFORE you run it. Other than that, I wouldn't think that mark will cause any issues otherwise.

If you're concerned about the gouge don't be except for whatever caused it.
I sucked something into a brand new top end and gouged the piston but it didn't affect the ring area which is most important.
What you have there is NOTHING compared to the gouge on my piston.
I know it makes you feel funny, same here.
I've been running that piston in my '74 YZ all last year and she's happy as can be.