81 250r How to tell piston size?

[CodyRosa]

Hi, I just seized my 250r this morning and am going to bore it but first need the piston size! I was told it was bored 0.30 over.. but I think its all stock.. The piston doesn't have any numbers on the top like normal. On the inside it looks like a 3, and H, and ART ?? Once again those 3 things are on the inside of the piston.

Im only finding stock pistons and wiseco pistons for this and its not a wiseco for sure. Looks pretty dang stock to me!

[Bren_downe]

Take it to a machine shop and they can measure your bore and let you know which piston to buy.

How did you seize it?

[CodyRosa]

I have no machine shops nearby.. I have no idea.. I was just riding on the road about half throttle.. I went to take a corner and let off the throttle and it made that hollow sound when i gave it gas.. and she came to a halt. barely put my foot on the kick start and it broke it loose. I'm not worried though.. it was low on compression anyways and the bottom end is still in great shape. I think I heard pinging? I didn't know what it was because i've never heard pinging but I'm guessing its what it was.

Locked up on the exhaust port side, intake sides piston skirt is half missing and no where to be found. Absolutely no marks on the crank, oils clean BUT there is a ton of crap in the exhaust port AND the inside of my pipe is whitish color.

[90guy]

Here is a good video for you.
https://www.youtube.com/watch?v=hdTW_RBR3Aw