Douglas 1920 4HP 595cc 2 cyl sv 3508

Douglas 1920 4 HP 595 cc side valve flat twin frame# 12877 engine # 11559

This Bristol-based firm develops the horizontally opposed fore-aft unit in about 1907 and continues utilising this engine layout well into the thirties. The earliest Douglas models have direct belt drive, but in 1910 a two-speed gearbox is added, with the control on top of the petrol tank. Douglas machines become very popular because of their lightness, ease of starting and speed: in the 1912 Junior TT races Douglas takes first, second and fourth places. In the First World War thousands of 2 ¾ HP machines are commissioned for use by despatch riders and they perform splendidly. In 1915 a 595 cc model with bore x stroke of 74.5 x 68 mm is introduced to cater for the need for a more powerful sidecar puller. Many of these 4 HP combinations are subsequently welcomed by the armed forces. A notable difference in engine design with the 2 ¾ HP model is the wet sump oiling system. In 1916 the 4 HP model is improved in a number of ways. To mention a few: other front forks, new design of exhaust, frame and tank alterations, front and rear brake changes and many small engine design improvements. To sum it up: quite another machine! Between 1916 and 1921 hardly any changes are made and at the 1921 Olympia Show the company remarks: “The 4 HP Douglas remains practically unaltered for the experience gained during the war under extremely unfavourable conditions has made the machine eminently satisfactory in its present form.” The 4 HP disappears from the range in 1924.

The machine we present here has been painstakingly restored some 20 years ago and has seen hardly any use since. She’s been proudly displayed in a Douglas enthousiast’s collection and will benefit from some checks before bringing her back on the road again. This 4 HP is a pleasant, easy to start and vibration-free machine and will certainly make her owner proud at any rally. She comes with foot-operated clutch, full acetylene lighting, Desmo bulb horn, BTH magneto and Amac carb. Also included is a small info file with some restoration photos and more than two dozen invoices relating to restoration work or parts.