Metal on metal

I fired the engine up yesterday after putting in the donor lm7
. Ran into a problem there's a bad sort of knock sounds like metal on metal at wierd intervals I have no experience with internals if anybody could help diagnose whether this is a big expensive problem or just something minor . The sound seems to be coming from te passenger head

Here's a link to te sound
http://youtu.be/159w9VVNylw

Probably a broken valve or a spring. If your lucky it's just a lifter that is collapsed. But metal on metal sound is probably a valve bouncing off your piston. Pull the valve cover and see if there's anything obvious.