Hi guys i have a 01 yamaha raptor 660. I need to replace the valve stem seals on it so i decided while im taking everything apart ill check out the piston and piston rings. How do i tell what piston i have? I looked online at yamaha and they gave 3 piston options std, .50mm, 1.00mm. If i measure the pistion across it's 100mm. the top of the piston says 3YF and below that at the bottom it says E X. Thanks