Hi, I just bought a 2002 cr125 that was used by a Canadian national pro in a few races, anyway it's been ported and has a high-compression head, full bills pipe, suspension, etc... It's also only run on race gas. My question is how often should I change the piston/rings? I race at the Junior level in canada ( I think that's the "C" class in the states but I may be wrong ) I've heard 10 hrs per topend but I'm not sure if that's also for modified motors. Thanks, Thomas