I bought this CRF 450 3 years ago and it has served me very well, engine is strong, no weird noise, doesnt burn a drop of oil between oil change (10hrs). Since i bought it, i have put approx 90hrs. Using Rotella T 5W40 Synthetic both sides. I do some wood riding, running from 1st gear to 4th most of the time. Cruising between 4000-5500Rpm (Digital RPM), sometime up to 6500RPM (Wheelie). Once in a while in 5th gear at 5500RPM during half mile stetch. With the type of riding i do, should i consider rebuilding the engine.... it is running so well i just cannot imagine that it will eventually fail. I dont know if the piston and Cylinder is original, since there is no way to check with the original owner since he is no longuer in the area... When i purchased the bike, i did replace the intake valves (Honda Brand) and i have set the clearance to 0.004 Last fall they were still at 0.004 and i assume they are still there now. Also i wanted to be sure that all were within specs inside the engine, so i did remove the Cylinder and piston, all was within specs, the piston skirt was almost all black.... just fading a little at the center of the skirt. Took the mesurements.... all was fine. Now, 90hrs later.... with my type of riding.... is there a reason to beleive that a rebuild is needed ? thanks.