Prototype 1948 Series B Vincent Black Shadow

The very first Black Shadow
By Phillip Tooth
July/August 2009
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Prototype 1948 Vincent Series B Black Shadow
Phillip Tooth

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Prototype 1948 Series B Vincent Black Shadow
Years made:
Claimed power: 55hp @ 5,700rpm
Top speed: 122-128mph
Engine type: 998cc air-cooled, 50-degree V-twin
Weight: 458lb (208kg)
MPG: 55-65mpg

“MAXIMUM SPEED: NOT OBTAINED.” Those four words must have set the pulses of thousands of enthusiasts racing when they read the first road test report of the Series B Vincent Rapide in May 1947.

And why wasn’t a maximum speed hit? The test rider couldn’t find a private road with a long enough run-in to get an average two-way maximum in top gear! With 56mph available in first gear, 86mph in second and 98mph in third, the Rapide was quicker than most other motorcycles — with a gear to spare. And with an all-new 998cc unit-construction alloy engine, almost straight handlebars, light alloy mudguards and a sprung frame, the Vincent looked every millimeter the sporting rider’s dream. The catalogue proclaimed: “The world’s fastest standard motorcycle!” and “This is a Fact — not a Slogan.” The Vincent Rapide was King of the Road. But not for long.

Beginnings of the Vincent Black Shadow
A year later and just a few weeks before the 1948 Isle of Man TT, Phil Vincent sent a note to the editor of Motor Cycling magazine with the tantalizing promise: “… in the Island will be a ‘Black Shadow’ for your transport and road test to follow … .” The Vincent Black Shadow was based on an early Rapide that had been tuned by factory tester and racer George Brown, his brother Cliff, and designer Phil Irvin. The engine came from a road bike they thought was too mechanically noisy to be sold. The Rapide was raced and sprinted for a year, often setting lap records, and was even tested by Motor Cycling magazine. The journalist was so impressed with the performance that he used a quote from a famous Rudyard Kipling poem about an Indian water carrier who saved the life of a British soldier as an introduction to his report:

‘Tho’ I’ve belted you an’ flayed you
By the livin’ Gawd that made you
You’re a better man than I am, Gunga Din.’

After that, George Brown’s Rapide was known as Gunga Din. When Phil Vincent decided to build a production version, he ordered the engine stove enameled black to give the new model a dignified appearance to match the name. Not everyone at the Stevenage factory liked the idea of covering that glorious alloy engine in paint, but Phil Vincent was proved right when the Black Shadow went on to outsell the Rapide.

Differences between the Black Shadow and the standard Rapide included polished valve rockers, ports, combustion chambers and connecting rods. The compression ratio was increased 6.45:1 to 7.3:1 and 1-1/8-inch Amal 289s replaced the Rapide's 1-1/16-inch carbs. Triple valve springs (instead of dual) were used, but the cams were the same as the Rapide's. First gear was changed 9:1 to 7.2:1. The cycle parts were the same as used on the Rapide, except for the ribbed cast iron drums that replaced pressed steel units.

The first Black Shadow was fitted with a prototype 150mph Smiths speedometer. Chief engineer Phil Irving chose a huge 5-inch dial, as used on sports cars, with a housing made from an aluminum saucepan. Marked in 10mph intervals, the dial was mounted directly in front so the rider didn't have to glance down to confirm the high speeds the Shadow was designed for. This style of speedometer was soon replaced by one with a neater, cast alloy case with the markings from 10 to 150mph in 20mph increments.

For the rest of the story featuring large, full-color photos of the Prototype 1948 Series B Vincent Black Shadow, order the July/August 2009 issue of Motorcycle Classics. Contact Customer Service at (800) 880-7567 or contact us by email. 

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