Gilera runner fxr 180 piston

I have bored my cylinder because it had a few spots but i used the old original piston because it was still good. Now i want to change the piston but i dont know which one should i get because there are 4 different sizes (65.55, 65.56, 65.57, 65.58). How do i know which one should i get?

 

You should check the original piston what type it is, then measure your cylinder.

 

Original is 65.55 but i dont know how to measure the cylinder

 

Find someone who has the right tools for it and they will measure it.

 

You can't re-bore a nicasil barrel !