The trail riding gods were angry today my friends...... Please recall that about 6 months ago I had a massive failure where my piston at itself up, plugging the oil screens and wobbling so bad that it touched the intake valves, bending them all. If you missed it you can read about it in this thread. Then read the latest story. http://www.thumpertalk.com/forum/showthread.php?t=206326&parentpage=2 I just got my Rekluse clutch installed and looked forward to testing it out on my unsuspecting 2 stroke buddy and his YZ250. We were riding on some leased property and did on lap about 5 miles long. The Rekluse clutch is phenomenal!! I didn't fall once and was able to stay with my buddy although, in his defense, he was breaking in a new top end on his bike so he was taking it pretty easy. Things went well as we finished the first lap and headed back to the truck. Just as I was pulling up to park I heard a very loud grinding noise and the motor just stopped. Everyone around me heard it and they all came over asking, "what was that?". "I dunno", says I. "I just put this new clutch in so maybe something broke", I continued. My wife grabbed the tools and I pointed to the clutch cover and she went to work while I got a quick drink. We popped the bike on its side and took the clutch apart but couldn't find anything wrong. I didn't think we would since I thought the noise sounded like a cam chain. Since the motor was froze solid it was time to load the bike up and go home to assess the true damage. Back in the driveway we popped the bike on its other side and I decided to take a look at the bottom of the cam chain first to see if there was anything obviously wrong there. I didn't think I'd find much there either but it was an easy check before pulling the valve cover off. My chief mechanic went to work again. Not seeing anything obvious we had no choice but to tear into the top end. Immediately after pulling the valve cover off we saw the source of the noise. At first glance it appeared that the shim bucket had shattered as there were pieces all over the place. We took the NEW exhaust cam out and found even more pieces and parts missing. We started pulling pieces out with a magnet. This is what we pulled out. You can see the shim all buggered up there along with the retainer clip and what left of the bucket. As you can see in this picture, the lifter bore is all chewed up as well and I'm starting to get real worried and see nothing but $$$$$ in my future. Damn, I just spent $1300 putting this motor back together earlier this year (about 15 hours on the bike at most since the rebuild) At this point I figured I broke a NEW exhaust valve and that's what caused the problem. As we pulled the head off and looked in the bore we saw the head of the valve embedded in the top of the piston along with the rest of the pieces and parts of exhaust valve train components. It was at this time that I turned the head over and saw the serious damage. Even more surprising was the fact that the exhaust valve was intact but it was the intake valve head that had popped off! Unbelievable. The intake valves were all brand new as well. In addition to the lifter bores being shot the head is pretty bunged up and the valve seat is shot. In my opinion the head is going to need to be replaced. Surprisingly, the piston bore is in great condition. With so little time on the rebuild I figure I could probably just buy a piston and reuse the rings but I'll probably hone the cylinder and get new rings anyway but reuse the piston pin that was new at the rebuild. I will replace the head along with all new valves and seals. I will probably reuse the valve springs and remaining keeps and lifters. The new 450 exhaust cam lob was pretty chewed up so that will have to be replaced as well. I guess the good thing is that I found out I LOVE the Rekluse clutch and that it didn't strand me on the trail 5 miles out or so. Keep in mind, this damage was cause with the bike almost at idle as I was coasting to a stop and with the Rekluse clutch this is just over idle.