After a long week end ride in the Mountains, I washed my 2000 WR400, Started it up to dry off, it sounded fine. I took the air filter out, cleaned it and re oiled it. I then packed it on the truck and went back to the mointains for another week end of riding. When we got to the camp site, I went to fire up the bike and it started making this terrable knoking sound. I shut it down and loaded the bike back up and spent the rest of the weekend riding other bikes. My mechanic pulled the engine apart and belives that the piston rod bearings had worn enough to cause the piston to hit the valves. I need a new rod, bearings, timing chain, ect. Does this sound right? He said if the Bike was an XR, I would still be riding it. The clearances in the WR are much tighter. If the bike was not YZ timed, would the valves clearances be so tight. This bike has alot of miles on it, but it ran great the previous week end. How could it get so bad so fast?