I'm in the process of re-building my YZ426 engine and I can't decide what to include. I've checked the valve clearences, and they check fine. The cylinder has good crosshatch marks. The head has your basic carbon build-up on it. I was thinking of replacing the piston with a Wiseco (standard compression) piston. Can the valves be replaced with lighter replacements? Originally, I cleaned up the intake and exhaust ports that had some casting marks and that improved the performace a little. I'm looking to do a low level engine re-build to make it respond a little better and bring back some life into an old engine. All advice is welcome!