The BMW heads cracked because they had high stress and failed under fatigue.

I duh know... I war reading about aircraft engine overhauls somewhere on the Interwebs.

My bro-in-law and his girlfriend have a couple of planes. I don't trust him enough as a pilot or a mechanic to go up with him. One of their planes is a ~30 years old single-engine and they use it to go back and forth between Miami and the Bahamas. No thanks.