Vincent Comet SSEngine: 636cc air-cooled OHV 4-stroke single, 90mm x 100mm bore and stroke, 10:1 compression ratio, 45hp (calculated)
Top speed: 115mph (est.)
Carburetion: 36mm Mikuni
Transmission: 4-speed Norton gearbox, chain final drive
Electrics: 12v generator, BT-H electronic magneto
Frame/wheelbase: 1-inch-diameter steel tube backbone w/engine as a stressed member
Suspension: Vincent Girdraulic front, Vincent swing fork, single spring/damper unit rear
Brakes: Three 7in (178mm) SLS drums, two front, one rear
Tires: 100/90 x 19in front, 110/90 x 18in rear
Weight: 375lb (170kg)
Seat height: 31in (787mm)
Fuel capacity/MPG: 5gal (18.9ltr)/50-60mpg
Although best known for its thundering V-twins, Vincent always included a 500cc single in its model range. That is, until the Series D models of 1955.
The 636cc single is fed by a 36mm Mikuni carb.
Vincent showed two prototypes of a Series D single — the fully enclosed Victor and a naked Comet — but neither went into production. Series D enthusiast Tony Cording decided he would build his own. First, though, a little history.
In the decade after World War II, Vincent’s position as builder of the world’s fastest street bike was threatened by ever-quicker and more powerful parallel twins. First BSA then Triumph established record speeds of over 150mph on the salt. The Rapide’s 45 horsepower and the Shadow’s 55 horsepower were impressive — as was their unmatched torque — but by 1955, a street Tiger 110 was making 40 horsepower and BSA’s Super Flash claimed 42 horsepower, with more to come. Vincent’s rear suspension was no longer unique with the almost universal adoption of swinging fork style suspension. While the quality of design and build of the Vincent was unparalleled, the competition was improving all the time.
Sales of Vincent motorcycles declined in the early 1950s, and after a failed government contract for the Picador drone aircraft engine, Vincent ran into financial difficulties. After restructuring his company in 1953, Philip Vincent decided to take his product line in a different direction.
Blame the Italians!
By the mid-1950s, scooter sales were beginning to outpace motorcycles in the U.K. From a negligible number in 1950, motorcycle imports grew to around 60,000 a year in 1955 — or a third of U.K. motorcycle production. Most of the imports were scooters from Italy, Germany and Eastern Europe, sold on the idea that they were cleaner and more modern because of their streamlined bodywork.
Seeing the trend, but committed as they were to big-wheel, full-size motorcycles, many British manufacturers decided that the answer was to enclose their motorcycles with body panels. Triumph had the Bathtub, Norton the Dominator Deluxe, Velocette the Special and Veeline models. British makers also designed brand-new motorcycles around the concept, like the Ariel Leader and Velocette Vogue. Or they just wrapped fiberglass panels around utility machines intending to disguise the fact that underneath was the same old commuter bike. Some, like BSA/Triumph (Sunbeam/Tigress), Velocette (Viceroy), DMW (Deemster) produced their own scooters. However, they somehow always seemed clunky and awkward compared with the sleek and chic Vespa and Lambretta. BSA and Velocette apart, most were built around the ubiquitous but aging Villiers 2-stroke engine. Seeing the writing on the wall, Douglas threw in the towel early and contracted with Piaggio to build Vespas in England.
Where many of the British builders went wrong was in assuming that the traditional sporting motorcyclist — responsible for the bulk of full-size bike sales — wanted his 500 single or 650 twin covered up. That proved not to be the case. Most buyers of bathtub Triumphs ditched the body panels — which accounts for their scarcity today.
The Vincent Series D
As always, though, Philip Vincent went his own way. Where his motorcycles excelled was in long-distance, high-speed touring. To capitalize on this, and to introduce a new and unprecedented level of rider and passenger comfort, Vincent embraced the idea of a fully enclosed motorcycle. Effectively he was going after what we would now call the sport-touring market. But in the mid-Fifties, this market barely existed, and didn’t really develop until the BMW R100RS of 1976. Vincent was around 20 years too early.
Black Knight and Black Prince
Philip Vincent’s aim was to provide the discerning rider with a high-speed tourer: “a two-wheeled Bentley,” as he reportedly described it. To achieve his aim, the Vincent Rapide and Shadow twins (and by implication, the 500cc singles) underwent some significant changes for the new “D” series of 1954.
The cool Lucas battery box. Vincent-batterybox.
Mechanically, the engines and transmissions stayed pretty much the same, though reports imply that the factory’s practice of selecting components, especially cams, to optimize the performance of production engines, was abandoned. The engine was fueled by the new, more compact Amal Monobloc carburetors, which allowed the fitting of two “front” cylinder heads with the carburetors on the left, as on the Black Lightning. Electrics were now by Lucas, not Miller as on previous Vincents, with a DC generator, and battery/coil ignition replacing the magneto.
The drivetrain was mated to a new chassis: a 1-inch-diameter steel tube replaced the series B/C “UFM” box section upper frame member (which doubled as the oil tank) connecting the rear suspension to the steering head. A new, separate oil tank was mounted on the rear subframe. The rear suspension was also modified to use a single Armstrong spring/damper unit in place of spring boxes and a friction damper. The seat was now fully sprung, unlike the C series seat which was attached to the rear “swingarm” and therefore articulated. A novel feature was the centerstand, which was deployed by a hand lever on the bike’s left side. The Shadow’s iconic 5-inch Smiths speedometer was deleted, replaced by a 3-inch unit in the headlight. The tough-to-find 20-inch wheels/tires were dropped, replaced by 3.5 x 19-inch front and 4 x 18-inch rear, and the “Tommy bar” wheel spindles were abandoned in favor of regular hex nuts.
“Any color …”
The series D Black Prince with the Shadow engine, and Black Knight, based on the Rapide, were fully enclosed in black-enameled fiberglass bodywork in three sections: the rear section encircled the bike from the gas tank back and around the back wheel; the front section acted as an air scoop to maintain engine cooling and also incorporated leg shields; and the headlight fairing included the front fender and a large windshield. Black was the only color available.
Tony Cording and his one-of-a-kind, hand-built Vincent Comet SS.
Vincent struggled to find a supply of fiberglass body panels in sufficient quantity and to their demanding quality standards. In order to maintain a supply of motorcycles, Black Prince and Black Knight models were built and sold without the bodywork, with the names reverting to Rapide and Black Shadow. In all, just around 450 Series D twins were sold, with as many as half being the naked versions. On the Series D, the crankcases were bare on both the Shadow and the Rapide, rather than the fully enameled Black Shadow Series C engine. However, the timing cover and the clutch cover were black on both D models.
But what about the series D singles? Just one fully enclosed Victor was built as a prototype. It consisted of the familiar Vincent 500cc single with a Burman gearbox, and it was fitted with Series D chassis and ancillaries. The bodywork was the same as the Knight/Prince. Just one naked D single was made, again using the D frame spec. Its fate is unknown, at least with any level of certainty.
Tony Cording’s Series D “Comet SS” Special
Tony Cording’s passion for Series D Vincents earned him the title “The D Man” within the Vincent community. But his introduction to Vincents in general and the Series D in particular came about by accident.
“I was a lover of Vincents from the age of 16, but I was not able to realize my dream of owning a V-twin Vincent until 1975.”
That was the year Cording attended a Vincent Section meeting in Toronto, Canada, and met a man named Barry Norton, who was heard saying, “My Vincent. I’m getting rid of it.” Cording inquired if he was serious: “He said, ‘Yes, I am,’ and I said, ‘I’ll buy it.’ I have a picture of me the next day picking up the bike with the registration, but I didn’t know it was a Series D. To me it was just a Vincent.”
With input from other Vincent owners, Cording soon noticed the significant variances between his Series D Rapide and the earlier Series B and C. “Completely different motorcycles but with the same engine,” he says.
“The Series D was not well received by Vincent owners. To this day, the average Vincent owner will take a Series C over a Series D any day of the week. However, I fell in love with the Series D. One year later I bought a Series D Black Shadow and two years later I bought a Series D Black Prince. So I became the Series D guy.”
Series D models are less common than C’s, though, Cording says. “There were 8,327 series C’s built and only 452 series D’s. My first exposure to a Series C was when I bought a basket case Comet.”
With help from Vincent guru John McDougall (now deceased) and ace machinist Dan Smith, Cording assembled a replica Grey Flash race bike which he ran at the now defunct Westwood race circuit outside Vancouver, B.C. He found the experience of riding a C very different. “On a Series D you cannot feel the rear wheel going up and down, but on a Series C you can, because of the articulated suspension affecting the seat.”
After selling the Flash, Cording immediately regretted his decision. “It was a very fast single and I thought how nice it would’ve been to have converted that Grey Flash to a street machine,” Tony says. “I was in England with my friend Jack Marshall — he’s the guy that introduced me to Vincents in 1956 — and bewailing my misfortune at having unwisely sold the Comet. He said, ‘Come out the back,’ and he gave me the crankcases, flywheels, and rear swingarm from a Series C and said, ‘These are for you.’ So I had them shipped back to Canada and John McDougall and I discussed what we would do with the engine.”
“Ultimately we said, ‘Well, if we’re going to have a single we should make it as big as we can.’ We decided to make it into a 636cc because that was the biggest crankcase mouth opening for an oversized piston.”
Both bore and stroke were enlarged giving 90mm x 100mm instead of the stock 84mm x 90mm. McDougall specified the piston for a 10:1 compression ratio, with a squish-band matched to the cylinder head, then gas-flowed the ports. Carburetion was by a 36mm Mikuni with a BT-H electronic magneto providing sparks.
“That was when I said, ‘I’m a Series D man; why don’t we make it into a Series D Comet Super Sport?’ And that’s what we did. Philosophically, to my mind, this could have been the ultimate Vincent single.” The next challenge was building the chassis. Cording was able to find most of the D chassis components and/or modify them to suit. Using the same Girdraulic fork as the C, Cording also located the correct series D steering head and swingarm, and 5-gallon (U.S.) tank. (The series C tank was 3.75 Imperial/4.5 U.S.) Black Shadow brake drums were fitted up front with Rapide drums at the rear attached to alloy wheel rims. A fully suspended Series D seat was fitted. “There’s a lot of genuine Series D stuff in this bike,” Cording says.
Cording is also baffled as to why Vincent didn’t make a similar bike themselves:
“Of the 8,327 Series C’s produced, 3,951 were Comets,” he says. “So the potential for Vincent to make a large, Gold Star-ish street machine of an enlarged capacity was there. But the only big singles around were Panthers, and (Norton) Big Fours and stuff like that.”
What is it like on the road?
“It is quick. It’s excellent to ride. It rides just like a Series D. Comfortable as heck. John (McDougall) calculated with compression ratio and gearing that it would do 115 miles an hour. I’ve never gone up to that kind of speed and never likely to, but that was John’s calculation.
“I took it to Texas last year for the North American Vincent rally and rode the 350 miles between Austin and Alpine, Texas, no problem at all. Good fuel consumption. Easy to start. So it’s a nice machine,” John says.
Really? Starting a 636cc single with high compression is easy?
“I’ve got to be honest with you, I had to relearn the starting procedure because I tried to start it the same way as I would a twin. It’s got a valve-decompressor, of course.” And applying the correct technique, “It’s no problem to start,” he says.
What’s Cording’s opinion of his finished Comet Super Sport?
“It was a continuation of a love affair with the Series D. The open D, to me, with its new suspension, modern ignition, and more modern electrics, was a cut above the Series C. But it was never seen as being that way.”
What about the much-maligned bodywork on the Series D twins?
“The enclosed D is a love-it-or-hate-it machine. The Black Prince was my number one Vincent ride for 25 years. I went everywhere, and was known as The D Man. I always enjoyed the ‘slings and arrows.’ Funny enough, when I sold the Prince, which was the last of my D’s, and bought a Series C Rapide, I really missed that fairing.” MC