In the process of trying to find out what is broken in the engine we have discovered metal shavings & a couple of pieces in the bottom of the pan. Can anyone tell me what would cause this?

How big are the pieces?

Usually bits of metal are bearings. Could also hypothetically be pieces of valves.

I'd lean toward bearings. If you had peices of valves make it to the oil pan, chances are you would be looking at replacing the block and head too.