Ok guys here is the story, I bought a 99 Yzf400 about 1 month ago, rode it twice the first day, about 2 hours in the morning & 1 hr that night, on the second ride the bike died, turned out that it bent an intake valve. I fixed the valve checked the clearances, one little nick in the piston so I left it alone. Got the bike running again took it up to the mountain it ran for about 5 - 10 minutes up the road and then 'clink' it died again! This time it broke a valve and chewed up the piston and head. Let me say here that I was sure I had the timing right, the bike would start, idle & rev just fine, it rode pretty good but started to develop a miss just before it died. That isn't the end of it, last night I just put it back together again, new piston, different head with a couple new valves, checked all valve clearances again, triple checked the timing, got it running again, took it back up to the mountain and the same thing happened, valve broke, piston and head screwed! What is wrong with this thing. Anyone have any ideas???? Is the crank somehow bad, could the timing chain be stretched out, could the tensioner be bad?? Please help this bike has now cost me over $3000 in purchase price and repairs and it is broken again. Thanks in advance.