Verdant Velo
Classic Bike Guide|June 2017

Sporting sophistication for clubmen and commuters

Marion Thirsk

THE VELOCETTE VIPER and Venom sports singles were introduced in 1955. Charles Udall designed both bikes to share the ohv singles’ exceptionally sturdy bottom end. The 499cc Venom used a 86mm bore and stroke, while a smaller 72mm bore gave the Viper 349cc. Renowned for being largely vibration-free, the Viper was seriously speedy for a 1950s 350 pushrod single. It offered smooth, swift acceleration which was aided by a close ratio gearbox, and a top speed of over 90mph was easily reached.

Velocettes were run and tested by managers and staff so any issues were quickly identified and sorted out, which obviously benefitted the buying public. In 1961 a Velocette Venom set the record for the first motorcycle to average over 100mph for 24 hours. A team of riders including Bertie Goodman, Veloce sales director, and Motor Cycling’s journalist Bruce Main-Smith averaged 100.05mph for over 24 hours at the notoriously bumpy Circuit De Vitesse, Montlhéry, France. No mean feat when you consider the Venom had no headlamp and the unlit track was illuminated by a series of car headlamps connected to batteries   which created a hypnotic strobe effect on the riders! A similar attempt on a Viper in 1963 was sadly thwarted due to the failure of a specially made sandcast piston. Leaving that aside, the Viper definitely has its own charms. As with many smaller capacity machines, it can be easier to live with than its bigger sibling.

The early Vipers had an Alfin alloy barrel with a bonded cast iron liner (this was replaced by a cast iron barrel in later years), a split skirt piston giving a higher compression ratio and a light alloy cylinder head with hairpin valve springs. In typical Velocette fashion the timing gears are really efficient. Fine pitch gearwheels drive the high camshaft and magneto while the dynamo is belt driven from the end of the crankshaft.

Rather than locating the clutch in the primary chaincase with the final drive sprocket separating it from the gearbox, the Viper’s clutch is located between the gearbox and the gearbox final drive sprocket. With just three nuts to undo, this made it easy for road testers at the time, who could quickly swap between sprockets while testing top speed and acceleration.

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