So I just finished rebuilding my 04 RMZ 250 - new crank, rod, piston, intake valves, etc. but I didn't replace the timing chain because the previous owner told me it was new, and I had only rode the bike 10 times or so. I'm now thinking that wasn't a very intelligent move, as last week I landed off a jump (this is my 4th ride since rebuilding) and she started knocking loudly. I tore apart the top end tonight to discover the cam timing was off. The chain must of slipped on the bottom sprocket because the cams themselves seemed to be still aligned to each other. Can anyone offer any advice as too what I should replace now (aside from the chain)? It was running when I shut it off, should I chance the valves being okay, or? I have heard this is a common problem with these bikes, is there a 'common' fix, or a mod to prevent this from happening again?