Crank Destroyed-Pistons Destroyed-why?

I've had a '76 nova for 7 years, 4 of which it sat in a garage untouched. I drove down to Tallahasee and back (probably not a good idea) to visit my friend and get it painted. On the way back, the crank pully and balancer ripped clean off while I drove. The key notch where the balancer is fastened to was ripped off and a gauge made at the end of the crankshaft rendering it useless. Fast forward to rebuild. After removing the heads, the #2,#5,#8 piston all appear to have been chisel pounded with a hammer and metal chunks in the chamber of the knarled piston. The heads caught some of the damage as well.
I do have a hot cam and ported heads with a weiend manifold topped off with a 650 Edlebrock carb. The timing was advanced to allow for mid-range torque. It's attached to a turbo-350 trans
I have pictures of everything. I hope someone can help me out and tell me what happened as I am certainly no expert in engine building.  

Chisel marks in the pistons sounds like the valves were beating the snot out of the pistons. Sounds like the balancer caused your crank pulley failure. How old was the balancer? Was it the original balancer?

What might have happened for the valves to hammer the pistons, the timing chain might have slipped a tooth (or been installed that way originally) and thrown the valve timing off. What kind of timing chain was installed on the motor before the rebuild?  

Well, I don't know what balancer was on it originally, but it was on it for a long time before this happened. Upon the removal of the heads and looking at the valves, they looked fine. The valves didn't appear to be damaged, just the wall of the combustion chamber in the heads were beat up. I didn't take the heads off until after installing a new crank and balancer and pully because my guess was that the balancer was not installed correctly. Could this have happened with about one minute of the engine running? Does this take a while to occur?
The timing chain was a double tooth chain, just like what comes on standard 350's.
The threads inside the crank nose where the bolt went was not damaged so I suspected it may not have been placed in by the people that worked on my car, but that is only speculation.
Looking back, we may have not corrected the problem but made it worse. I thought of the valves too, but I'm puzzled because they're in good shape. Is there anything else? or are the valves just that tough?  

I've had this happen to me and have seen it with many other Chevy damper installations. A couple cases seem to be at work here; one is the retention bolt comes loose and falls out. Second, GM went thru many cost cutting phases and one place they saved a few pennies a few years back was eliminating the damper bolt, the theory being it's a press fit and that should hold it inplace, for a mildly driven grocery getter it works for an engine that can put some real twist on the shaft it doesn't work so well. The damper coming off, especially if you're leaning on the engine a little, can be pretty messy. It carves up the end of the crank pretty good and I've seen 'em bust the snout off cast cranks or bend forged ones right at the #1 main.

Secondary failures like your upper end damage is often seen as well. As the damper comes loose the crank gets some wild moments put into it and these things can really flex and dance. Add that to your 4 degree advanced cam which might actually be 8 degrees advanced because a lot of cam grinders have been building in 4 degrees of advance for a lot of years now and Comp is a big offender. So if the cam wasn't baseline indexed, so you know where you're really at, when the engine was build but rather somebody just tossed a 4 degree bushing in there, it's a pretty good bet the cam has way more advance than you think.

The timing advance combined with the flexing crank probably caused the pistons and valves to meet. The stainless valves are a lot tougher than the aluminum pistons so the pistons appear to get the worst of it. But if you pop (or try to pop) the valves out, I'd expect you'll find bent stems. If the valves closed with bent stems, you can bet the guides are toast as well. Consider your timing set to be junk as well since it got slammed back and forth to its limits a few times and for all pratical purposes is now worn out or worse with flattened bearing surfaces inside the chain and perhaps indents in the gear teeth an rollers.

Boige  

So I took the heads to a speed shop and he quickly discovered that the valve seat in the number one chamber exhaust side busted apart in the chamber and "floated" through 2 more chambers. He blamed it on shotty head work by a machine shop. I find this hard to believe because I drove that car a lot before this happened. Is it that "matter of time" thing? I guess with the aluminum chunks in the chamber, that it was a trickle down effect to the whole rotating assembly. I also removed the camshaft and the first lobe was completely ground down- junk. I don't think there is a single part that I can reuse inside that engine, and I got no money. So I'm selling the car now which sucks because the tranny and rear gears are fantastic along with everything else but the engine. Oh well.  

I wouldn't sell the car yet or give up hope. You could always find a junkyard 350 of some sort for cheap, give it a mild refresh and put it in your Nova so it still drives. You can do a slow build up from there, heads, cam, etc. Do some swap meet hunting for parts, use the carb and intake form the old motor.  

I'm with Phill, you'll long regret getting rid of this car, just hunt down a decent used or rebuilt engine and slowly start back.
Even a new GM Goodwrench can be had for less than a junker car you'd buy to replace the Nova. Keep it.

As for the cam and hard seat problems, these are not uncommon for an engine that sat a while. Chevy has had lots of cam problems even with aftermarket sticks. Letting an engine sit for a long time without using it allows the lubrication to dry out and cam lobes and lifters don't do well when that happens, you need to go back with an engine that's sat a long time and put cam lube on em like when you're building a fresh motor. This probably fired up with a dry lobe, actually many dry lobes, and this one got the worst of it. I'm a huge fan of cam buttons, the idea of using the spin angle on the lobe to force the lifters to maintain buffer clearance is a bad idea. On pre roller blocks you're well advised to run a button to take this load off the lifters and lobes, they've got plenty else to do getting valves opened and closed, especially if you jack up the spring pressure and run higher lift cams and possibly 1.6 rockers all these things add to the forces the lobes and lifters have to resolve.

Hard seats in aluminum are always a problem especially in an engine that isn't used a lot. A piece of steel pressed into a chunk of aluminum makes a battery in the presense of an electrolyte like water. Water is the major product of combustion, not to mention what seeps into an engine from the atmosphere. A little water and a lot of time and the aluminum begins to corrode around and under the hardseat. Next thing you know the seat comes loose. It might have gotten some dymanic help when the crank damper came off as well since some pretty heavy vibs went thru the engine in that moment.

Bogie