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Technical Curiosities: The Sleeve Valve

February 27, 2012 by Matt

Knight Sleeve Valve Engine Motor

This technical curiosity is a personal favorite of mine. Used a few high-end pre-WW2 cars, the sleeve valve was far better known for its exploits during the war inside a number of renowned aero engines developed by the British firms Napier and Bristol.

A different method of controlling intake and expulsion of the air/fuel mixture, the sleeve valve system dispenses with conventional valvetrain, including poppet valves, spring, rocker arms and pushrods. Instead, a cylindrical sleeve nestles between the piston itself and the wall of the engine block. The sleeve rotates and moves vertically, its motion controlled by a shaft driven off the crankshaft further down in the block. Ports in the side of the sleeve admit the mixture and allow exhaust gases to be expelled in sync with the movement of the piston, and a conventional spark plug in the roof of the combustion chamber provides the ignition source.

The sleeve valve was a solution to the difficulties posed by conventional poppet valves of the pre-WW2 era. Metallurgy being in a more primitive state then than now, the internal sealing of most engines was less than ideal, and virtually all engines burned a degree of oil as a matter of course, whether they used poppet or sleeve valves. Before advances in sealing that would later vault poppets past sleeve valves in engineers’ consideration, sleeves presented a number of important advantages over their counterparts.

Sleeve Valve Engine Motor Schematic Diagram Drawing Operation How It Works

Without the inertial restrictions of spring-actuated valves, the engine can spin much faster without worrying about valve float and piston-to-valve contact. Also, with careful shaping of the ports, intake and exhaust timing can be precisely controlled, and port area can be much greater than with poppets, unrestricted by the size of the combustion chamber ceiling. Without 2-4 valves per cylinder, the valvetrain is greatly simplified, and the spark plug can be located in the optimum location in the combustion chamber, unencumbered by valves.

Given these major advantages, why aren’t we all driving cars with sleeve valve engines? Sealing. As with the rotary engine, sealing is and will always be the major difficulty of the sleeve valve engine. Not only do the piston rings have to fit tightly against the inside of the sleeve, the outside of the sleeve itself must press up against the block wall. And given that all these parts move relative to each other, they must be lubricated, and some oil leakage into the combustion chamber is virtually guaranteed. As mentioned, during the engine’s heyday, poppet engines were just as bad, so there were virtually no downsides to the sleeve valve engine, but after the war, great strides in materials and processes allowed poppet valves to trump sleeves, sealing-wise, and the sleeve valve engine faded away. It’s a shame, really; given consistent development time, the engine might have overcome its issues, and blossomed into the superior configuration, since it is a fundamentally more efficient design than engines on the road today.

Editor’s note: This post is part of an ongoing series spotlighting obscure automotive engineering solutions. Read the other installments here:

Filed under: Technical, Technical Curiosities

1 Comment

  1. areopagitica says:

    The neoprene stem seals turned brittle and crumbled on my Stude V8. The rocker chambers received too much oil and the valve stems were submerged all the time. Perhaps the hot oil did them in. Afterwards part throttle vacuum pulled the oil down the guides and it coked on the back side of the intake valve. So thick it choked off the flow. Just a little oil getting into the combustion chamber lowered the octane rating of the fuel charge. The answer was not to have shaft mounted rockers needing so much lubrication, and to restrict the upper end oil delivery, something Chevy invented in 1955. I don’t know what the Kent (Fiesta) did, since it had shafts, but it never consumed oil.

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