Velocette Viper Clubman

From 1960 Velocette produced the Viper in a "Clubman" racing version, fitted with TT Amal carburettors, a BTH racing magneto and a close ratio gearbox, with the compression ratio raised to 9.3 to 1. The Clubman dispensed with the unpopular glass fibre enclosure and instead made a feature of its highly polished crankcase and gearbox castings. Supplied with "rearset" controls, lowered handlebars and a steering damper, the Clubman also had a range of optional accessories including a "megaphone" exhaust silencer, a rev counter and light alloy wheel rims.

In 1963, a little over a year after their successful '24-hour at 100mph' record (using a 500cc Venom), the Veloce factory decided to make a second attempt at a 24-hour record, using a 350cc 'Viper' model, which had been specially tuned for the purpose.

Both attempts took place with an Anglo-French team at the Montlhéry speed bowl, a 2.7km concrete track, with a notoriously bumpy surface and rather poor facilities, especially track lighting. Obviously, if a machine is to be run for 24 hours, the track needs to be lighted, and Montlhéry is distinctly dark at night, being outside the small suburb, and in a forest. Both attempts used rows of parked cars with headlamps ablaze, to light the track at intervals - notably dangerous when you consider that each 'beam' was a perpendicular flash of light at 100mph, creating a dizzying stroboscopic effect. During the earlier Venom 24hr ride, a French rider became so disoriented late he ran off the track, derailing the whole exercise for half an hour, while the machine was sorted out. The team still had time in hand, and just squeaked over the magic 'ton', at 100.05mph for the 24 hours.
 

The Viper model as standard shares the cycle parts of the 500cc Venom, as was common in the cost-cutting British industry at the time, so it bore a weight handicap relative to its larger brother, at 380lbs. And while the Venom is 'square' at 86mm bore/stroke, the Viper is decidedly a long-stroke, using 72 x 86mm dimensions (a 'sleeved-down' Venom engine, with smaller combustion chamber, valve size, and inlet tract/carburetor).

The 350cc Viper used in the 1963 attempt was a very special machine, and hardly 'standard'. The most radical departure from catalog spec was a dry-sump gearbox with an oil pump, which sprayed oil from jets onto the gears, then recirculated the lubricant, to keep the oil cool and reduce drag, and saved a few horsepower. The TT carb had its float bowl remotely mounted on the oil tank, a la the pukka racing KTT model, the exhaust valve was filled with sodium for cooling, an unsilenced reverse-cone megaphone, and full Avonaire racing fairing (adding 6-10mph to the top speed) were used. The piston was a specially sand-cast item shaped to give a 10:1 compression ratio (the 24-hr Venom used 8.75:1). This piston eventually put paid to the whole attempt, when the crown separated from the body above the gudgeon pin. Ivan Rhodes speculates that the ignition misfires and a fairing bracket which partially masked the cylinder head could have raised temperatures enough to cause failure of the piston. In any case, the two difficulties encountered during the attempt - a misfire from the magneto and the broken piston - were from components not made by Veloce! Small consolation for a failed attempt.

The Viper was more comfortable than the '61 Venom, as the front forks now had both compression damping and rebound damping; this 'extra' was recently introduced to their sporting 'Clubman' models, and really helped over Montlhéry's bumps. The steering and true-running were faultless, even when airborne over those bumps at over 100mph.

The machine was geared to reach 110mph (176km/hr) at 6500rpm, and after 6 hours, the Viper had an average speed of 104.7mph; faster thus far than the '61 Venom. The hourly average, excluding pit stops of 75 seconds each, was 105.1mph, which was fully 23mph faster than the existing class record, established in 1961 by a 175cc Bultaco two-stroke.

The “Viper” was running with complete regularity and seems ready to equal the 'Venom’s' 24-hour 100.03 mph of 1961. It was, in fact, improving slightly on the '500's' speed.

However, the second attempt, started at 10.40 a.m. on Sunday, failed after 1 hour 44 min. at an average of 102.5 mph with suspected gudgeon-pin fracture which it was quite clear that factory mechanic, Jack Passant, could not remedy in time to keep the average above 100 mph.

The 'Viper' was permanently disabled and the extent of the damage could be determined until the head and barrel were lifted at Hall Green later that week.

Source: The Vintagent