Lot No: 325
1928 Zenith-JAP 680 Racing Motorcycle
Frame no. 10424
Engine no. GTOY/C1955
Zenith motorcycles were manufactured from 1904 until 1950, in a variety of factories in or around London. From the early days proprietary engines were used, such as Fafnir, Precision, JAP, Bradshaw and Villiers. The driving force behind Zenith was Chief Engineer, and company owner, Frederick Barnes, who was responsible for the famous 'Gradua' gear. Worked by a hand-wheel or crank handle, the Gradua mechanism varied the diameter of the engine pulley while simultaneously sliding the rear wheel back and forth in the fork slots, thus maintaining correct belt tension. Its advantages showed most effectively in speed hill climbs, and in pre-WW1 days Zenith machines gained many successes as the Zenith rider could change gear during the ascent while the other competitors had to make do with a single choice of ratio. Rival riders and manufacturers thought that this was an unfair advantage so many leading club