It’s nearly forgotten now, but at one time there were thousands of cars on the road with engines unlike anything of today. Let’s look at the sleeve-valve Willys-Knight.

This is not a history of the Knight sleeve-valve engine. That’s an entire tale in itself. Long story short: While it was invented by an American, Charles Y. Knight, in around 1905, the engine first found favor in Europe, where it was produced under license by multiple manufacturers, including Mercedes and Daimler of England. Here in the USA    a few years later, John North Willys of Willys-Overland acquired a license as well and launched production of the Willys-Knight in 1914-15.

While there were numerous Knight licensees in the United States, Willys-Knight was by far the most successful, producing 50,000 cars or more each year, and at one point many believed the Knight system would obsolete the conventional poppet-valve engine (the kind we know).  That’s rather stunning to contemplate, as to modern eyes, the Knight engine is strange indeed. This is simply a brief—and clear, we hope—look at how it’s put together and how it works.

In the early years of the auto industry, poppet intake and exhaust valves were noisy, troublesome, and required ceaseless maintenance. Next to tires, they were arguably the greatest annoyance of auto ownership. Charles Knight’s ingenious remedy was a pair of reciprocating sleeve valves, one inside the other and concentric with each cylinder, driven by an eccentric shaft that ran at half crankshaft speed, like a conventional camshaft. The twin sleeves were quieter and offered more flexibility than his initial design, in which the entire cylinder reciprocated up and down.

Above are the basic components of one cylinder in an inline six-cylinder Willys-Knight engine. The piston is a conventional T-slot aluminum component, while the two small connecting rods transmit the motion of the eccentric shaft to the inner and outer sleeves. At upper left is the cap that forms the combustion chamber, seals the cylinder, and locates the tops of the  sleeves, known as a “junk head” in Knight lingo.  While there were variations in the engines of individual Knight licensees, the Willys-Knight is typical.

The critical components, the sleeves, were gray cast iron, precision-ground on the inside and outside, around .125-in in wall thickness, with grooves to retain oil for lubrication. Cast iron was chosen for its stability, machineability, and wear properties. The intake ports were cut on one side of the sleeve diameters and the exhaust ports on the other, so in that regard the Knight could be considered a cross-flow engine.

Despite all the strange-looking components, in operation the Knight is a conventional Otto four-stroke engine, with the familiar intake, compression, power, and exhaust phases (left to right above). The clean combustion chamber design, with no exhaust valve or hot spots, allowed a somewhat higher effective compression ratio. Aside from some thermal issues, there was little constraint on the size of the ports, while at times the sleeves are moving in the same or opposite direction, so most any practical valve timing could be achieved.

But the real advantage of the Knight was its utter silence and smoothness. With no poppet valves to clatter or misbehave, the engine rightly earned the name “silent Knight.” Disadvantages? There were those, too. They included the generous reciprocating weight of the sleeve mechanism, along with excessive combustion blow-by and oil consumption. However, the resulting carbon buildup on the sleeves over time actually helped to seal the cylinders. Willys-Overland advertised the Knight as “the only engine that improves with use,” and that was perfectly true. Another drawback was manufacturing cost, so the Willys-Knight was the company’s premium product, while the rest of the line used conventional poppet-valve engines.

From the start through 1925, Willys-Knights were mainly inline fours, and from 1925 on, inline sixes until the end. The four was considered equal in smoothness to a conventional six and the six equal to an eight. (There was a Falcon-Knight companion brand, too.) However, in 1917-19 the company produced the Willys-Knight 8-88, a V8 with two main bearings and a single eccentric shaft in the middle of the vee (above). In the Willys-Knight’s final form, the “advanced 1933” 66E six (actually produced in 1932) displaced 255 cubic inches and produced 87 horsepower.

The Knight engine patents expired in 1932, and in that same year Willys-Overland went bust and the Willys-Knight was discontinued. But in reality, the Knight engine’s time had already passed. Through improved materials and manufacturing, the problems of poppet valves were effectively solved and the Knight no longer had any particular advantage. But there was a time when there were hundreds of thousands of cars on the road powered by engines that were unlike anything today.