The Sleeve-Valve Engine…by Ray Katzell
As a fancier and owner of Minerva automobiles, I have often been asked questions about their sleeve valves. So here goes.
Although the principle of the sliding or sleeve valve was not original with Charles Y. Knight, it was his patented version that caught on with a number of automobile manufacturers starting with English Daimler in their 1909 models. Minerva also produced its first engines based on the Knight principle in May of that year.
Other Full Classics™ that have used sleeve-valve engines include Voisin, Stearns-Knight, and Willys-Knight.
One of the clearest explanations I have seen of the Knight sleeve-valve design appeared in a Minerva instruction book, so it is reproduced here. The accompanying figures help explain the text.
“In each cylinder slide two concentric sleeves, which have each on their upper part two diametrically opposite ports. These sleeves are moved up and down in the cylinder, so that the ports coincide at determined moments with others provided in each cylinder wall, thus establishing the connection with the inlet or the exhaust manifold. The upper part of the sleeves slides between the cylinder and the cylinder head, and three small rings and a wide one prevent gas leakage. The last ring shuts off the ports in the sleeves when these are in their upper position. The piston does not move in the cylinder, but within the inner sleeve.
“This alternating movement of the sleeves is controlled by a [camshaft] which revolves at half the speed of the crankshaft. This [camshaft] carries as many eccentrics as there are sleeves and each eccentric is connected by a rod to its sleeve…The position of the eccentrics is established so as to cause the ports to coincide with a determined timing…
“Briefly every cylinder has two sleeves, two connecting rods and two eccentrics,”
as well as a piston which moves up and down within the inner sleeve.Most of the Minerva Full Classics™ are in-line six-cylinder versions of about six litre displacement, but there are some smaller sixes as well as a few straight-eights of the 1930’s. Voisin developed several different configurations of sleeve-valve engines, including eight- and twelve-cylinder jobs, each in both straight and vee layouts.
Why the sleeve valve? The conventional poppet valves of the first quarter of the Twentieth Century suffered from clatter, imprecise seating, broken springs, burnt exhaust valves, and rapid wear (frequent “carbon and valve jobs” were necessary and costly. Although modern improvements in design, metallurgy, and lubrication have minimized those problems, the best solution at the time seemed, to Knight and many other engineers, to be the sleeve valve.
An article in the
Indianapolis Star of December 11, 1927 aptly described some of the advantages of the Knight design, as follows. “From its very inception, the Knight sleeve-valve engine has been of high compression design…The successful high-compression performance of the Knight sleevevalve engine is attributed to its distinctive design, independent automotive engineers pointing out that this type of power plant seems to be unusually well adapted to high efficiency work, many of them declaring that for such service it is superior to the best poppet-valve engine.“It is pointed out that the combustion chamber in the Knight sleeve-valve engine is distinctive for its freedom from detonation. This is brought about by the smoothly machined surface of the head and walls, with no projecting edges. Also the shape of the combustion chamber in the Knight sleeve-valve engine is a true cylinder surmounted with a dome-shaped head, and it is claimed that this is the ideal design for obtaining the greatest degree of efficiency from an engine of the high compression type.
“The spark plug is located in the exact center of the compressed fuel charge, with the result that the spark has the shortest possible distance to travel. Since there are no odd-shaped spaces in the Knight sleeve-valve engine for gases to be confined in when the piston compresses the mixture ready for firing, the entire bulk of the explosive charge is confined directly above the piston.
“In all, it is the compactness of the sleeve-valve combustion chamber that places this type of engine as ideal for high compression performance.”
However, the sleeve valve too had its problems, among them high cost,oil consumption and internal inertia (the criticism that they were not amenable to high speeds is belied by many excellent racing records compiled by Knight engined cars, including a flawless 5th-place performance by a Mercedes-Knight in the 1913 Indy 500). As the years rolled on, the ratio of pluses to minuses gradually lessened relative to poppet valves so that, by 1940, sleeve-valved engines faded into history along with their last user, Minerva.
Courtesy of
Classic Driver of the Delaware Valley Region