Hankering back to boyhood, I was browsing a few sites for the latest in Model Aircraft Engines.

I came upon <A HREF="http://.www.rcvengines">http://.www.rcvengines</A>.

The "RCV" is for Rotary Cylinder Valve.
The cylinder comprises a rotary inner sleeve, geared to rotate at half crankshaft speed and containing the porting in the head. As the sleeve rotates, it uncovers the inlet port, on compression it uncovers the plug (glow plug in this case) then the ehaustt port. The engine operates on the four stroke cycle.
One design is of the conventional vertical cylinder configuration. There is an unusual design whereby the actual propeller drive is taken from the end of the horizontal rotating inner cylinder. This enables larger props to be driven at half engine speed, ideal for vintage scale models.
I was taken back to the days of the Barr and Stroud Sleeve Valve engine with a combination of the Cross and Aspin rotary valves.
I understand that the RCV Engine company has ventured into small motor cycle engines.
Now, with the benefit of modern materials and precision CNC machining, the old ideas are coming back as a reality.