I bought my YZ400f 3 months ago and i'm replacing the piston rings on a STD piston. I do not know if the piston that is on the bike at the moment is the OEM or an aftermarket one. How can i tell? Is there some kind of a code on the OEM? Do the OEM rings fit on any piston(aftermarket)? Bore= 92.0mm. Piston=91.5mm I will appreciate Any help. Thanks.