This is a NEW Cayden Cycle BIG Boy B1 51.00mm (made in Japan)(10-11 to 1 compression ratio) piston kit & aftermarket top end gasket set. See piston comparison in pic #2, OEM piston is on the right side. This kit will make your bike a 92cc. NOTE: installing this kit will require you to bore & hone your stock cylinder, but no re-sleeve is required.