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Rotary valves are perfect for two-stroke engines, but a way of using rotary valve principles in a four stroke engine had not been perfected until George Coates had his brainwave.
He decided that the poppet valve should be replaced by a rotating sphere, hollowed out to provide a passage for the inlet charge or exhaust gases, with openings timed and shaped to alternately expose or close the respective ports, to coincide with the up-and-down movement of the pistons.
Looks simple at fist glance. Looks often deceive though, as they do in this instance, because the problem of sealing the spherical valve in the head, against the pressures of combustion, is not an easy one to solve, and it is why the use of new materials that have only recently become available that make this invention possible . In the case of the Coates design the spheres are sealed using a patented carbon-ceramic.
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