[freshblake]

I can't see how he would get pre engagement with shaving the 3rd and 4th teeth.

It looks like he did all that shaving to do exactly that - prevent PE. Unfortunately it created a lot of stress on the other teeth on the piston which is why it stripped and he was able to get 1k rounds.

If he had a crazy thick sorbo on the cylinder head his piston would be sitting too far back thus creating a poor angle of engagement opposite to the original angle he was trying to correct.

Assuming the first tooth is already removed you only need to brush that second tooth with a file and ensure the cylinder head has the proper thickness of spacer for a proper AoE.