Memorable Motorcycle: Vincent Comet 1950

Frank Melling | July 3, 2015

I once had a girlfriend just like the Vincent Comet. She was clever, pretty and enthusiastic in every respect: you really couldn’t fault her as a person. The problem was that she had a younger sister who was even brighter, stunningly beautiful and was legendary in her enthusiasm for those activities for which she was ideally suited. Whenever the two ladies were seen together, my girlfriend was virtually ignored while her sister was worshiped.

This is the situation in which the Comet finds itself. The 500cc Single is a thoroughbred and an admirable motorcycle in every way. The problem is that the 1000cc Vincent Rapides and Black Shadows are considered to be even more exotic, and therefore vastly more desirable. However, owners of twin-cylinder Vincents shouldn’t get too far above their $300,000 stations in life because their machines are directly descended from the 500cc Singles which were Vincent’s first, mass-produced motorcycles.

1950 Vincent Comet
The motor is willing, and very torquey, in an archetypal, British sporting Single way but it does vibrate fiercely. It pulls hard, and will romp up towards its top speed of a genuine 90 mph without feeling stressed.

The story starts in 1926 when the young Philip Conrad Vincent, born and educated in England but the son of wealthy cattle ranch owners in Argentina, went to Cambridge University to study Mechanical Sciences. By this time, Vincent knew a lot about motorcycles and had decided to become a manufacturer in his own right – a practical dream, given his parents’ wealth.

Young Philip persuaded Dad Vincent to put up the money for his first bike in 1927, and the MAG-engined 350cc Single was an apparent success, completing some 10,000 miles of test running without an issue. (MAG being the Swiss-based engine manufacturer Motosacoche Acacias Genève.)

The Vincents, father and son, were serious about Philip’s ambitions and so when the failed HRD motorcycle company came on the market in 1928, it was bought on the basis that the HRD name was known, and respected, in the bike world whereas Vincent was completely unknown.

The young Vincent was ambitious right from the start and wanted to offer the public fully sprung rear suspension and a very clever triangulated frame, which was the true predecessor of today’s perimeter chassis. To say the least, Vincent was a pioneer.

Clever though he was as a creative engineer, Philip would have starved without his Dad’s money behind him because his new motorcycles trickled out of the Stevenage factory in miniscule numbers. Only four of the 24 different models he made in 1934 ever made it to production – and using the word production is being more than very kind. Vincent used Villiers, MAG, Blackburne, JAP and Rudge engines, but the commercial reality of actually producing a bike for sale always inclined him towards the JAP single-cylinder motors.

The problem was the variable quality of the JAP engines. Things came to a head with a batch of super special JAP racing engines which Vincent purchased for his 1934 Senior TT bikes: they were a disaster!

1950 Vincent Comet
The Vincent Comet’s push rod engine is a masterpiece of efficient engineering.

Vincent later wrote: “After these experiences, we never wanted to see another JAP engine as long as we lived, and decided that we should design and manufacture our own.

“Fortunately, I had available Phil Irving, who in my opinion is one of the best conventional motorcycle engineers in the world, with an amazing knowledge of all the good things that other people were doing currently, down to the fine design details.

“I myself have ever been an inventive type of designer, always seeking to incorporate details which would represent a worthwhile and big advance over previous designs.

“In the subsequent design, which evolved over a few months, I had to keep my own instincts fairly in check because we could not spare the time to prove satisfactorily many unconventional features, so we tended to lean heavily on Phil’s remarkable working knowledge of our competitors’ efforts.”

It’s fair to assume that, left to his own devices, Vincent would have produced an overhead cam design of the sort sold by Norton and Velocette or perhaps a chain driven overhead cam motor in the style of the AJS R7. The problem was that overhead cam engines required precision engineering which posed real technical problems for 1930s manufacturers. As a result, all the exotic overhead cam machines lost money for their makers.

What Vincent conceived, and Irving executed, was a wonderfully neat push-rod engine which offered almost all of the advantages of an overhead cam engine but which was much easier, and cheaper, to make.

The key challenge with a push-rod engine is the imprecise opening of the valves at anything other than modest rpm. Vincent and Irving largely solved the issue by having the camshaft mounted high in the engine, meaning that the push-rods were short and very stiff which in turn gave precise opening of the valves. Each valve ran in two valve guides, again for accuracy, and was opened by a forked rocker arm.

1950 Vincent Comet
The Comet’s triangulated rear suspension was decades ahead of its time.

After a few, initial problems with high oil consumption the new engine was an immediate success and was sold in three forms: the touring “Meteor”, a super sports “Comet” and a full on racing version – the “TT Replica.”

All the engines were 84 x 90mm giving a capacity of 499cc – which resulted in a very respectable 28 horsepower at 5800 rpm. On the road, this equated to a real 90 mph – a science fiction fast speed when there was almost nowhere in Britain where this could be achieved on a public road.

What was just as interesting is that the Comet had almost the same performance as the 350cc Velocette KSS – a sophisticated overhead cam design which cost Velocette money on every sale.

Good as the Comet was, its real claim to fame came about by accident – or this, at least, is one of the most wonderful folk tales in the whole of motorcycling. In 1936, Phil Irving was playing about with a tracing paper copy of the Comet engine. He realized, so the story goes, that if he canted one Comet engine backwards and another forwards, and left a 47 degree space between the two, he would have a neat, compact, 998cc V-Twin which would produce a solid 45 horsepower. The legendary Vincent Twins had been born.

The new motorcycle was called the Rapide and it became both an instant success and a failure. The new bike’s performance was incredible but completely destroyed the proprietary Burman gearboxes which had been designed to handle half the horsepower of the Vincent Twins. Even so, 77 customers bought the new Superbike before the outbreak of the Second World War in 1939.

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Frank Melling

Contributing Editor |Articles | Our Memorable Motorcycles expert, Frank Melling also is the organizer of the British vintage motorcycle extravaganza known as Thundersprint. Melling began riding five decades ago and remains as much in love with motorcycles as when he drove his first bike into a cow shed wall aged ten. In the last 50 years, Melling has competed in every form of motorcycle sport and now declares himself to be too old to grow up and be sensible.

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