Norton 598cc Model 19 OHV 1935
In 1933, the engine of the Model 19 had been revised with a bore of 83mm and stroke of 113mm, increasing its capacity to 596cc. Other recent upgrades included enclosed valve gear, and the magneto was moved from the front of the engine the rear for better weather protection.
More information: Norton Model 19
Image adapted from a catalogue posted by Howard Burrows