I'm no expert, but I'm pretty sure the knock sensor didn't/couldn't pull enough timing out of it?

Edit: changed the subject line...didn't realize it was only one word.

What is the usual cause of the ring lands breaking off? I'm assuming detonation but haven't broken enough parts to know. I think I will rebuild the thing most likely with forged pistons, but I don't plan on a blower like the previous owner had.