I believe the head gasket failed on my engine.
There was a loud bang, then the sound of air puffing at high pressure. I discovered that air was coming out between the cylinder block and head by the #6 spark plug. I didn't find any pieces of the head gasket, nor any discernible holes, as the hole would be very thin, but you can definitely hear and feel the air coming out. I think there was a small amount of oil expelled, probably only a few drops; there was no noticeable spattering of oil on the side of the engine bay or battery.
I was wondering if anyone has anyone ever heard of this happening? Since it's a sturdy material and compressed there should be n reason for the material to be forced out from between the two tightly-fitted metal surfaces, but high pressure and heat can do interesting things. It should not be much of a problem to install a new head gasket, and I would also replace the intake manifold gasket as well; it weeps a little oil too.
I'll need to get the model numbers from the cylinder head, block, and intake, then order gaskets. The engine is a stock L28 with the dished pistons, IIRC, so there's no reason to get any "performance" gasket or is this an opportunity to improve things slightly? The thing spins easily when cranking.