'One's outstanding impression is of the exceptional flexibility and smoothness of the engine – it seems almost incredible that so much docile punch should be the product of no more than one cylinder and an 8.5:1 compression ratio,' enthused Motor Cycling about its test Viper, summarising characteristics that will be familiar to anyone who has ever ridden one of Hall Green's delightful high-camshaft singles.
The high-performance 500cc Venom and its 350cc sibling, the Viper, were launched in 1956. The MSS frame and forks were retained for the newcomers while full-width alloy hubs were adopted to boost braking power and smart chromed mudguards fitted to enhance the models' sporting image.
This particular Viper had been laid up in dry storage for 40 years when the current vendor purchased it in 2011. The machine was then restored over a three-year period: 2011 to 2014. Works carried out included powder-coating the frame; fitting taper-roller steering head bearings; installing new swinging-arm trunnions and bushes; rewinding the magneto; fitting stainless steel mudguards; and installing a new wiring harness and battery. Two important upgrades have been incorporated: a Groves Classics anti-wet-sumping device and a solid-state voltage regulator. New tyres were fitted recently to the Borrani alloy rims. Described as in generally good condition, the machine is offered with sundry restoration invoices, an old-style continuation logbook, MoT to April 2017, and a V5C registration document.