Most likely the valve stem lock failed. If the end if the vavle itself snapped off I'd be surprised. No matter what your looking a t a rebuild. You may even have to check the block if the sleeve was damaged. 350 blocks are so cheap re sleeving isnt worth it IMO.
OK, so it's not in my Camaro, but I'm sure someone here can tell me. Last
> weekend the engine quit in my 1970 GMC pickup. I am in process of tearing it
> down right now. What I have discovered so far is the head of the exhaust
> valve on #7 is broken off. I have heard of this happening before, but this
> is the first time it has happened to me. I was hopping someone here could
> tell me what could cause this. The motor was completely rebuilt about 20k
> mi. ago. The heads are off a 1972 Impala. Since rebuilding the engine has
> never been overheated, and has never seen more than 5000 rpm.
>
> I am about to go back outside and pull the heads off now. I am prepared to
> find the worst. Thanks in advance for any information that could shed some
> light on this. - Gary
>
>