Howdy AVB,
NormK has mentioned in the past the pitiful compression you can get away with in Powertorques and it will still run and cut the lawn. I had a full crank 160 (predecessor to PT) with a regular piston inside an oversize cylinder that you could move the piston crown more than 1mm sideways with your fingers and it still ran. It stalled very easily though.

Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!