Just wondering. I have a 2011 YZ 450 F that has around 70 hours on it. I am almost 53, I ride well in the over 40 A class, and in the 45 and 50 classes, I am usually top dog. So I ride hard, but am no where near 450SX speed in my advanced age. I change the oil every ride (usually less than an hour time, or at least only one full tank anyhow) and use a Stainless steel oil filter. Used Devlac oil. I have never took the head cover off to check valves. Never sis it since I owned a 08 Honda 450. My 2009 and 2010 YZ's I traded in with 50 plus hours and they always started fine.So that's why I haven't checked them. In the engine, what would you change if you were to keep the bike? I figure just the piston and rings and such, but really not sure. This is going to be a practice bike, as it is now, and sometimes a HS bike. I am looking for reliability was thinking of just another OEM piston, but what are your thoughts on other pistons? How about higher compression pistons ( I still want to use just pump gas)? timing chain? when does that need replaced? Cranks? I seldom use the clutch, as I never have to adjust it, but ride with my finger on it everywhere. I am going to repack the muffler again using the steel tube insert and fiber matting material from Moose Racing. I do that every 20 hours. If I keep it, I will also do a full suspension rebuild with new bushings and seals. I haven't changed the oil in the shock or forks for 24 hours. In the past I have used KYB factory oil.