I am pretty sure it is the timing chain... what do you think??
400 EX timing chain and or valves vid # 2? (http://www.youtube.com/watch?v=80hsRXqlzkA#)
400EX timing chain ticking noise (http://www.youtube.com/watch?v=d6QeRQ8QuNw#)
Have you checked valve clearance? Either way put a crf400 or 450r (depending on your year) timing chain it it. My guess is timing chain.
Yea there were several things going on, The timing chain was really stretched, the valves were off and the tensioner was broken, dont know how it managed to run, but should be up to to specs in a few days
;) Guess it's a good thing that ya know your problem now. Unfortunately it's gonna require some work $ and downtime.