Classic Racer




The 1960s and 70s were exciting times in road-racing.

Grand Prix stars competed in nonchampio­nship internatio­nal class races on exotic works machines, National Championsh­ips were hotly contested in all classes and club racing at scores of tracks was often over-subscribed.

The UK scene was seeing an increase in production racing. The advantage of this class was two-fold: it gave manufactur­ers a chance to show off their high-performanc­e models at selected races and offered a way to enter the sport without having to purchase expensive ‘real’ race bikes.

Velocette Motorcycle­s embraced the new class to promote models of their single cylinder 350cc Viper and 500cc Venom machines.these bikes appeared dated, incorporat­ing features of their old single-cam KTT such as: narrow crankcase, dry-sump lubricatio­n, hairpin valve springs, and single down-tube cast lug frame with separate engine and gearbox.

A high camshaft push-rod design replaced the KTT bevel driven OHC.THE narrow pressed-up crankshaft spun on taper roller bearings assembled in the crankcases with a 0.004-inch ‘pinch’ or pre-load. At operating temperatur­e, expansion gave zero pre-load.

An H-section con-rod with a roller bearing big-end and plain bearing little-end supported the cast aluminium three-ring piston. An aluminium cylinder with cast iron sleeve, plus the aluminium head were secured to the crankcase with four through studs. A separate cover incorporat­ing the rockers and enclosing the hairpin valve springs bolted to the head.

The high mounted camshaft was driven by a gear train from the right end of the crankshaft; these gears also drove the rear-mounted magneto. Like the KTT, primary drive was by chain to the clutch inboard of the rear sprocket.

Looking like a museum piece, the cast lug/ tube frame did incorporat­e a novel solution to adjusting the characteri­stics of the rear suspension.the tops of the rear shocks could be pivoted around their lower swingarm fastenings from near upright position to a ‘lay-down’ position. Front suspension was by telescopic forks with rebound oil damping, the front axle located in front of the bottom sliders.

Although appearing old-fashioned, Velocette singles had excellent handling and performanc­e. In 1961, a near stock Venom set a world record, averaging over 100mph for 24 hours! High performanc­e parts were available

Mick Ofield

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