Vincent Black Shadow
Vincent Black Shadow Background & History
The Vincent Black Shadow was in production from 1948 through 1955. It was Vincent’s top-line performance machine and considered at the time one of the finest motorcycles ever built. Based on Vincent’s Rapide, which was already a very fast bike with a 110 mph top speed, the Black Shadow was capable of 125 mph. This made it the fastest production motorcycle in the world at the time. Over it’s life, the Vincent Black Shadow was built in three successive Series, as improvements were made.
This 1949 Vincent Black Shadow shows how good looking they were.
Vincent Black Shadow Engine Design
The engine of the Vincent Black Shadow was based on the Series B Vincent Rapide engine, which was a 1000cc (998cc actual displacement) V-twin with a 50-degree V-angle, not 45 like the Harley-Davidson V-twins. In fact, the prewar Series A Rapide had a V-angle of 47.5 degrees. But when civilian production resumed in 1946, the Series B Rapide had been completely reengineered, and part of it was the 50-degree V-angle. This was done to better accommodate the new frame that used the engine as a stressed member, thus eliminating about one-third of the frame.
The overhead valve (OHV) setup consisted of two gear-driven cams mounted high in the crankcase, each responsible for one cylinder. The short pushrods operated rocker arms that actuated the valves, which were unique in that they were supported by two valve guides, one high on the valve and one lower. This was thought to better support the valves for longer life, and it worked. Between these two valve guides, the forked rocker arms worked the valves. It was a novel system, done at a time when valve stability and the metallurgy of valve guides were questionable. This was typical of Vincent’s thinking, it was outside the box, clever, and seemed to work very well on the Vincent Black Shadow. With a bore of 84mm and a stroke of 90mm the engine was almost square, but just mildly undersquare (smaller bore than stroke). Vincent also engaged in something that few other British motorcycle makers had done, certainly at the time, the Vincent Black Shadow engine and gearbox were mated together in a single housing, which later came to be known as unit construction. It would take the British motorcycle industry by storm in the late 1950s and early 1960s. Vincent did it in 1948.
The Vincent Black Shadow was a technological tour-de-force back in its day. And look at the quality and finish of those components.
Rapide engines were always polished aluminum (silver colored), and all Vincent Black Shadows have the entire engine blacked out. Black Shadow engines were carefully selected from Rapide production, looking for the best examples. Parts were measured, weighed, inspected and hand-picked for their tighter tolerances. The intake and exhaust ports were meticulously sculpted, ground, blended and smoothed to improve flow. After World War 2, Britains motoring public was stuck with low octane ‘pool’ petrol which required a low compression ratio to prevent pre-detonation (pinging). While the Rapide had a low 6.8:1 compression ratio, the Vincent Black Shadow was bumped up to 7.3:1, part of the secret to the extra horsepower.
Series A Black Shadows (1948-1950) have a third valve spring, not used on the Rapide, but it was dropped on later series. Series A machines were prewar, everything built from 1946 on would be Series B or later. Series B and C (1951-1954) locate the spark plug for the front cylinder on the right side, while the rear plug is on the left. Series D bikes (1955) place both spark plugs on the right side. Series Ds also switched from dry sump to wet sump lubrication (oil external oil tank). Series B and C also ran 1-1/8-inch Amal 289 carburetors, which was larger than the Rapide’s. The ignition system was also upgraded for Series D with a switch to coil ignition from magneto, along with a Lucas DKX2A distributor. Series D used a 1-1/8-inch Amal 389/10 carburetors.
The Vincent Black Shadow engine is unitized with the gearbox all in a common case.
From a Single to a V-Twin
Prior to the war, Phil Irving, Vincent's chief engineer, was sitting at the drawing board with two tracings of the Vincent 499cc single-cylinder engine. As things got moved around, the top tracing roughly lined up withj the bottom one such that it made it look like a V-twin. With a little cajoling, he lined it all up and the Vincent V-twin was born. The likeness is so uncanny that the single looks the same as the V-twin except that it's missing the rear cylinder. The new 998cc V-twin was introduced in the 1936 Vincent Series A Rapide. It made 45 hp and was good for 100 mph, stellar at the time. It was produced in small numbers prior to World War 2. When it was reintroduced after the war in 1946, it had been completely reengineered and it was a monster. This in turn led to the Vincent Black Shadow, which was the hot rod version of the Rapide. But it all started with the lowly 499cc Vincent Comet single.
LEFT: The Vincent Comet 499cc single. RIGHT: The Vincent Rapide 998cc V-twin.
Painting a Vincent Black Shadow Engine
At a time when most engines are laden in chrome and polished aluminum, Vincent-owner Phil Vincent decreed that all Black Shadow engines would be finished in gloss black. To achieve just the right look, first a “pyluminising” coat of chromate anti-corrosion primer was applied, over which a layer of Pinchin & Johnson black enamel went on. The parts were then baked at 200-degrees F (93.3 C) for two full hours. Some believe that a black engine dissipates heater more rapidly than a silver engine. But the main advantage was the look. Because of the black engine, at a time when there weren’t many, made the Vincent Black Shadow all the more stunning visually.
The Vincent Black Shadow frame used the engine as a stressed member, and employed a novel rear frame member that resembles Harley's Softail in concept. Vincent called it 'cantilever suspension'.
Vincent Black Shadow Frame & Running Gear
The Vincent Black Shadow had just as much novelty in its frame and running gear as did it’s engine. The engine formed a stressed member, thus eliminating the frame downtube and engine cradle. Series B and C used an upper frame member (UFM) consisting of a fabricated sheetmetal box section that doubled as the external oil tank for the dry sump lubrication system. The steering head was an iron casting which bolted to it. For Series D which had a wet sump system, no oil tank was required so the UFM was built from steel tubing and brazed lugs, bolting up the same way. Great effort was put into weight reduction, along with lots of aluminum parts, bringing the weight to just 458 lbs. Sidecar mounts were optional.
The rear suspension of the Vincent Black Shadow and all Vincents for that matter was another novel system. They called it ‘cantilever suspension’. The entire rear frame section (called the rear frame member or RFM for short) pivoted on mounts at the rear of the gearbox, and was suspended by two roughly-horizontal shock absorbers that lived under the seat. In basic function it works very much like a Harley Softail, but the Harley puts the shocks under the engine and the Vincent has them under the seat. But the basic movement of the rear frame section are very similar. Suspension travel was augmented in Series D to a full 6 inches of wheel travel.
This 1951 Vincent Black Shadow Series C was the first year for the new Girdraulic forks.
Vincent Black Shadow Suspension
Up front, Vincent Black Shadow Series Bs used the same Brampton girder fork as did the Series B Rapides. The Black Shadow being more performance-oriented, the front suspension was stiffened to improved handling, at a slight penalty in ride quality. The Rapide has a 160 lb front spring and the Black Shadows used 180 lb springs. Starting with Series C Vincent’s own Girdraulic blade-type girder was used, and it had a hydraulic damper in place of the coil spring.
Vincent's unique front brake had two sides, a 5-inch drum and SLS backing plate on each side. That's the speedometer drive with the cable coming out the top.
Vincent Black Shadow Brakes
The brakes on the Vincent Black Shadow are another example of how far Vincent was willing to go to build the best, most advanced, fastest motorcycle in the world. Series B and C had two-sided brakes front and rear, each side being a single leading-shoe, 5-inch drum with Ferodo MR41 linings. However, where the front and rear wheels were interchangeable on the Vincent Rapide, they were not interchangeable on the Shadow.
One of the most famous photos in all of motorcycledom. Trademark of Harris Vincent Gallery, Inc.
The Bathing Suit Bike
Vincent wasn’t kidding about this “World’s Fastest Motorcycle”-thing. In 1948 the world speed record for a normally-aspirated motorcycle stood at 136.183 mph on a Harley. American John Edgar ordered a modified Vincent Black Shadow that would be purpose built to beat the record. The bike was so extensively modified that it earned a new name: Vincent Black Lightning. The bike was built and shipped to California Vincent dealer VL Margin, but not before it was test ridden at over 140 mph at the Grandson Aerodrome in England. On September 13, 1948, the Black Lightning appeared at the Bonneville Salt Flats in Utah where rider Rollie Free broke the standing record with a run of 148.6 mph. It was so close to 150 that Free kept trying. He finally concluded that the wind resistance from his leather riding suit was slowing him down. So he stripped down to a bathing suit, a bathing cap and a pair of slip-on deck shoes, removed the seat and laid prone on the back fender, and set a new record of 150.313 mph. The photo is the stuff of legend and forever marked the bike with the beloved nickname “the bathing suit bike”. I saw the original bathing suit bike, now fully restored, at the Quail Motorcycle Gathering in Carmel CA in 2016. I met the current owner and he made it clear that the owners of the bike did not appreciate it being called the bathing suit bike. They referred to it as the Black Lightning.
This is the exact same bike pictured above, just completely restored. I took this in 2016 at the Quail Motorcycle Gathering in Carmel CA.
Vincent Black Shadow Motorcycle Books
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"Illustrated Vincent Motorcycle Buyer's Guide" Loaded with all the info you need before you buy a Vincent, or bid on one in auction, illustrated. |
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By R M Clarke, 172 pagesReprints of motorcycle magazine articles, road tests, new model introductions, history, specs & more. |
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