It dropped a valve on the original owner. Then while in Moab, the valve train sounded funny so I took the valve cover off when I finished the trail and low and behold the spring retainer was cracked in half and about to drop another valve. It would have been really bad if it would have ended up dropping the valve while I was in the middle of nowhere on a very technical trail. Then replaced with stainless steel valves and the rockers wouldn't stay adjusted for very long. If I ever get another motorcross type bike again, it's back to a two stroke. I am probably just expecting to much out of that type of bike. It seemed several people at the time were having the same problems. My KX 250 was great on the trails.