As a friend of mine pointed out the "gearless" is actually a 4 tooth (pinion ?) running in an 8 tooth anulus - just very strange looking gears.
Some Possible Options / Changes / Improvements.
I originally intended to make the pins as rollers but since this was mostly a proof of concept I didn’t bother. Whilst it works, it is high friction and therefore low efficiency consequently it runs with a distinct knocking and does not turnover silky smooth when manually turned by the flywheel.
If the efficiency fell below 50% it would self-lock (i.e. be non-reversible - it's smooth when driven by the cylinder), I don’t think I’m near that limit but I would recommend rollers.
The Ø3 pinwheel mounting shaft and ball-bearings are a bit flimsy and I would recommend going to Ø4 but to do that the crank web would need to be 2mm thicker, the standoff columns 2mm longer and the footplate mounted 2mm further back to accommodate the wider (3 to 4mm wide) ball bearings.
And the valve conrod would need a 2mm dogleg as well.
I'll post the revised drawings, build notes - covering both engines now and a better video.