RE: Piston Ring Question......
FlyBy, Barry,
Most Schnürle ported engines have a pinned ring that cannot rotate. The gap would be oriented in one direction only, always.
Some baffle-piston engines have their ports multi-bridged; essentially splitting a large bypass into several small ones... that cannot catch a ring-end.
Such was the HB.40PDP, which had a free-to-rotate Dykes ring.