Question: Some years ago, a Southern California company (I believe it was Coates International) was making inroads with rotating spherical valves with promising results. Then, poof! No more info was available. What is your opinion on the potential of rotating spherical valves for internal-combustion engines?
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Answer: Many alternatives to the existing poppet-valve technology have been proposed. Short-lived torpedo engines have been run with thin rotating disc valves, valuable in this application because they reduce engine height, allowing more power to be packed into a standard 21-inch-diameter naval torpedo.
Velocette’s Harold Willis spent time and money trying to get the conical Aspin rotating valve to reach the performance level of two poppet valves. In the 1950s, Norton experimented with a Cross rotary valve, ultimately equaling the power of its poppet-valve “Manx” racing engine but with oil-control issues. A man with whom I once corresponded, Wilhelm Krautter, had been an engineer on the Mercedes T-80 land-speed car before the World War II and had come to the US under the “Paperclip” program. He had developed rotating ball valves for engine use, prototyping them on Honda singles.
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Ball geometry is uniquely attractive because it can be sealed by a single round ring, a feature not shared by either the Aspin or Cross types. In the Aspin, the rotating valve body takes the form of a cone, and sealing is accomplished by pressing the cone against its seat. In the Cross, a close fit between rotor and cylinder head is required. A flat disc rotor can be sealed by a round ring and may have been used in the ’50s in a motorcycle-based test engine by NSU engineer Walter Froede.
Other interesting types of non-poppet engine valves are shown and discussed in the late Philip H. Smith’s 1968 book, Valve Mechanisms for High-Speed Engines. More recently, inventors have been inspired by the segmented spring-backed seals used in Wankel engines, giving rise to a view that if the Wankel can be sealed well enough to reach production so could a rotating-valve piston engine.
A few years ago, it was confidently announced that rotating valves would shortly take over in Formula 1, eliminating traditional problems of valve float at high rpm. So far, this has not come to pass.
Coates CSRV V-twin 1600cc Motorcycle
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