Garside, who had been impressed by the
Fichtel & Sachs engine in both the
NSU Spider sports-car and a snowmobile, installed a bought-in F&S
air-cooled single-rotor engine into a
BSA B25 'Starfire' frame as a "proof of concept". This proved reliable and smooth, but under-powered. Garside then created a prototype twin-rotor engine (with F&S rotors), which doubled the capacity of the earlier test "mule". This twin-rotor engine was installed in a BSA A65 frame. (In Europe,
DKW later used a fan-cooled single-rotor F&S engine in the
DKW Hercules motorcycle, but this was less radical and much less powerful than the Norton Classic). Wankel engines run very hot, so Garside gave this air-cooled motor additional interior air-cooling. Filtered air was drawn through an intake that was forward-facing to provide a
ram air effect. This air was channelled initially to the rotating mainshaft and through the interior of the two rotors, then entering a large pressed-steel
plenum before entering the combustion chambers via twin carburettors. The plenum, which doubled as the bike's
semi-monocoque frame, enabled the transfer of much of the heat to the surrounding atmosphere. (This idea was taken from the
monocoque Ariel Arrow). The carburation process further reduced temperatures via the
heat of evaporation. Even so, at the fuel-air mixture was still hotter than ideal, and the engine's
volumetric efficiency remained somewhat impaired. The eccentric shaft's main bearings and the inlet manifolds were fed by oil-injection lubrication, and the fuel-air mix also carried residual mist of oil from the interior of the rotors, which helped to lubricate the rotor tips. == Notable innovations ==