I had to look that one up too... Once I saw it, I realized I've seen a design that used it before. I think they used them on some old motorcycle engines. It seems like the little pin and slots would wear pretty quickly, but it might work if it were part geneva mechanism, part normal gear..... it looks weird in my head and is probably not even possible, but now I want to draw one.

The idea is for it to work like a 4-position geneva mechanism for exhaust and intake, but use a normal gear to turn through the compression and power strokes. The way my valve is situated, the pressure from compression and power will make it seal more tightly, and also make it more difficult to turn during those strokes. So, it would be 1 position per stroke, but only for half of them... a half-linear gear of sorts.

You guys just keep making my brain go off on these nice mental exercises, and I think in the end it will result in very good things.