I have a 79 vette, and about a year ago the engine exploded. I now have the money to go through an engine replacement and fix/replace everything I need too to get it back on the road. A couple of days ago I started tearing the old block apart and clearing everything out of my engine compartment that I want to either get rid of or replace. After about 30 minutes I got down too the heads, and after pulling them off I found out exactly what had caused the engine damage (I knew it was going to be bad, I was pumping water out of my exhaust and pieces of my head were under my carb after it blew up) one of my exhaust valves broke off then impacted my head causing most of the chamber to shatter along with putting a hole in my piston large enough too fit my finger through. The piston expanded from the impact causing the cylinder to crack in three places vertically. After I first put the old engine together I was having valve lash problems from crapy polly locks. The polly locks were replaced and I did not have any valve lash problems for about 6 months before the engine went. All of my rockers seemed to be properly adjusted when I tore apart my block and now I am wondering what could have caused a valve to snap like that. The entire exhaust system is rusted and decaying, could it have been a high or low backpressure problem? From looking at the way that it broke and impacted it looks like the valve snapped off while it was open then tilted 45 degrees before the piston hit it on the next stroke. I need to know what caused this so I can prevent it from happening ever again, I love my vette and don't want to dish out the cash for another long block a few years down the road lol.

 

that sux. No telling what caused the original failure. Valve may have stuck open them got hit bu yhe piston, thats a good bet. Poly Locks usually back off when they go bad which would make the valve not open all the way, so not likely the problem. Were all the valve keepers in place?

So, building a bew engine, what to do, what to do?
383 stroker, crate motor, headers and all the other interesting parts?

 

Going with a 350 4 bolt main. I want a cam in it that will stay open around 30- 40% past BDC so i guess I need a 240- 250 cam. I don't realy need a stroker, compresion ratio should be around 9.5:1 so 70cc heads would be good with flat top pistons. I want to through a set of hooker headers and mufflers on it also. At the very least I will put after market manifolds on it and tear out the cat (won't have to fabricate a new Y pipe that way) If I do replace the entire exhaust system I should be able to go with 2.5 inch Y pipes and a 3.5 inch connecting pipe since [2.5^2]pi aprox = [1/2(3.5^2)pi].

 

Did you check the pushrod length? If the lifter rides of the valve stem it will in time drop the valve.

 

have you seen the bottom end yet? is the connecting rod still attached to the crankshaft for that cylinder?

 

Not knowing the whole story on your engine, the possibility of the valve sticking open is quite good. Years ago I had that problem on a freshly rebuilt head. I found the valve manufacturer had stamped the part number on the valve stem and the head shop forgot to buff them off when rebuilding the head. If you can get the valve stem out of the head, look for evidence of it binding in the guide.

 

I'm going to pull my heads apart now and check for that. You would think that they would bind for that reason only right after a rebuild though. The car had been running smooth for awhile before it snaped.

I haven't checked out the rest of the block yet, I'm letting it sit in the car until I am ready too put the new engine in.