zac510 wrote:... the timing and duration of the opening is still locked.
There is a Lotus design, circa 1990, for a variable opening and, I think, variable timing rotary valve, that uses a stator outside the valve carcasse and rotates the valve, shaped like a cylinder and acting as a rotor. The concept seems easy to implement, but the valve is subjected to the full engine compression, so I guess the sealing problem persisted.
More serious than the sealing disadvantage mentioned, compared to poppet valves that uses autoclave effect, the Aspen and Cross rotary valves (vertical and horizontal, respectively) suffered from overheating, lubrication spilling into the combustion chamber and spark plug fouling.
The only constructor of rotary valve engines I could find was Coates
. They claim they could double engine output by increasing compression ratios, because their rotary valves does not create hot points in the combustion chamber... I think it has to be taken with a grain of salt, as the one problem with other rotary valves has been that they interfere with the spark plug optimal position. Contrary to Aspen and Cross experiences, they claim they do not need coolant or lubrication on the engine head (?).