I went through this motor and did all valvetrain, had a machine shop fix up the head, followed all the torque specs, capacities, timing setup, etc. to a tee; I fired it up today, it ran smoothly for about 5 minutes then clattered like all hell.

Pulled the valve cover and it looks like one of the cam sprockets is suddenly misaligned?  What would cause this?  I've never done a DOHC motor before, only OHV stuff... maybe I overlooked something.

Kinda bummed I'm going to have to pull this motor again (can't get to the front cover without doing so), but would be nice from some guys who have more experience with OHC engines.

I'll grab a pic here in a minute.

Chain jumped, possibly the tensioner failed.

Well shit. I put a brand-new tensioner in it... but yeah, that would make sense. I thought it was low oil, causing it to seize hard, l but that doesn't seem to be the case with the valve cover pulled.