WOW...  Now that is    Hope you make out in the long run.   Can't wait to see the pictures of the valve and others. 

This is one time I hate to be right!!!
That's a real bummer, John.
I'd have to wonder about using that engine again. Might be best to start over, with something else. Sux tho, since you just got this one...
Good luck with whatever direction you go. I know you'll keep us updated!

I do have another question. What can cause this to happen? Is it anything I could have prevented in the brief time I've had the car?

I positively don't trust the block. It's going to the big engine playground in the sky. I'm leaning towards the ZZ4 route, but still not certain. Got to do some reading of old posts to get a feel for the options.

Could have been a bad valve, but a more likely culprit would be a keeper. There are different angles available for the keepers and the retainers, so it's possible that they weren't matched properly. Could have broken a valve spring, and that allowed the keepers to fly off. Many possibilities.
I doubt you were doing anything to create this problem while driving, unless you wound it up really tight, and missed a shift on a four speed. I'd guess it was faulty/miss-matched parts, or a fatiqued valve.

Was the corresponding valve spring broken when you pulled the valve cover?
Scott

If the valve guide is no good it can cause a valve to stick and it sounds like your original description may have indicated that the valve was sticking sometimes.  This will definitely bend the valve and eventually cause it to fail. 

Maybe you should just call this engine K19 (due to the green glow in the intake).  Should be rebuildable as long as the bores are ok.  Once you get everything apart I'd be checking for a bent rod and making sure the crank hasn't been damaged. 

I can't see why it won't be salvagable though, with a new pair of heads of course.

Chips5838876.9122916667

I honestly didn't look at the valve spring or the cylinder wall. I had already had enough that evening...

I'll look this evening to see what the total damage is.

If you have to start over, I would get the ZZ383 like "FLA VETTE" got for his ride vs. a ZZ4.  Just my opinion.  That is a bummer with your engine. I've been down that road a couple times myself. So I know how you feel. Good luck!

Sarge  

[QUOTE=jgoglick]

I honestly didn't look at the valve spring or the cylinder wall. I had already had enough that evening...

I'll look this evening to see what the total damage is.

[/QUOTE]

well, look on the bright side- it will be reborn with a kickass new powerplant, be it a crate engine or a rebuild. chances are it will be better than when you got it and youll love the car all the more!

Yup, it will be better than before. I'm looking at crate engine options. Seriously looked at the ZZ383, but not sure I want to spend that much. Has anyone used http://www.enginefactory.com/ ?

I looked at the cylinder wall, doesn't appear to be any damage. It looks like when the valve dropped, the valve stem went straight down, and was then pressed up into the compustion chamber, which caused the hole in the chamber, and serious gashes on the piston. I'm betting at best the rod is bent and the crank is damaged. At worst, and very likely, the block is cracked. I'm not going to rebuild it.