Vincent Comet

VINCENT COMET BACKGROUND
Vincent was a very low-volume producer of premium motorcycles. During the entire span of the company’s existence (1928-1955) they barely made 11,000 bikes. The big V-twin Rapides and Black Shadows may have been the stars of the show, but the 499cc single-cylinder Comet was their biggest seller, by a wide margin. So few V-twins were built that all the money was being made selling Comets. The Comet was a very advanced design for a British single of the day, with many features unique to Vincent. Most singles on the market at that time were considered entry-level ‘cooking’ bike (ie: cheap commuters), but Vincent took their singles in a whole new direction, building it into a truly premium machine that people aspired to own.

COMET ENGINE DESIGN
The Comet engine was an air-cooled 499cc OHV single with its camshaft set high in the crankcases. Both the cylinder block and cylinder head were made of aluminum alloy with a cast iron cylinder liner. The compression ratio was 7.3:1. These engines included a very unique valve arrangement with two valve guides on each valve with the forked rocker arms acting on that portion of the valves that laid between the two guides. This gave the valves more lateral support and a much straighter path. The Comet single served as the basis for the V-twin engine in the Vincent Black Shadow, they just doubled everything. The gearbox was a Burman BAP 4-speed, all set in a unit-construction case.

COMET RUNNING GEAR
The Comet had frame similar in layout to the V-twin Vincent Black Shadow which included Vincent’s proprietary cantilever rear suspension and Vincent’s Girdraulic forks up front. And, like the big V-twins, the engine was a stressed member of the frame, eliminating the need for front downtubes and an engine cradle. This saved weight and mass, and helped ‘the little Vincent’ punch well above its weight class.

COMET TIMES TWO
Prior to the War, Phil Irving, Vincent’s chief engineer, was sitting at the drawing board with two tracings of the Comet 499cc single-cylinder engine. As things got moved around, the top tracing roughly lined up with the bottom one at an angle that made it look like a V-twin. With a little cajoling, he lined it all up and the Vincent V-twin was born. The new 998cc 1936 Series A Rapide made 45 horsepower and was good for 110 mph, stellar at the time. It was produced in low numbers until civilian production was curtailed by World War II in 1939. After the War, it was completely redesigned and the 1946 Series B Rapide was a monster. They put two front brakes on it to counter the added speed. The Series C came out in 1948, with telescopic forks instead of the old girders. But the big news was the addition of a new high-performance version dubbed the Black Shadow, now making 55 hp and topping out at 125 mph, hence the title “The World’s Fastest Production Motorcycle”. Black Shadows are famous for their gloss black engines. Rapide engines were finished in polished alloy.

LEFT: Comet 499cc single engine.