Why do I keep blowing head gaskets?

I had issues with detonation, never heard it, but the evidence was clear by the material missing, pitting close to the edge of the piston top, opposite the spark plugs. Scrutinize the piston top. My rod bearings also lost "crush".

http://www.contactmagazine.com/Issue54/EngineBasics.html
nother thing detonation can cause is a sandblasted appearance to the top of the piston. The piston near the perimeter will typically have that kind of look if detonation occurs. It is a swiss-cheesy look on a microscopic basis. The detonation, the mechanical pounding, actually mechanically erodes or fatigues material out of the piston. You can typically expect to see that sanded look in the part of the chamber most distant from the spark plug, because if you think about it, you would ignite the flame front at the plug, it would travel across the chamber before it got to the farthest reaches of the chamber where the end gas spontaneously combusted. That's where you will see the effects of the detonation; you might see it at the hottest part of the chamber in some engines, possibly by the exhaust valves. In that case the end gas was heated to detonation by the residual heat in the valve.

Good luck