Douglas 1921 4 HP 596 cc side valve flat twin Frame # 13846 Engine # 12824
This Bristol-based firm developed the horizontally opposed fore-aft unit in about 1907 and continued utilising this engine layout well into the thirties.
The earliest Douglas models had direct belt drive, but in 1910 a two-speed gearbox was added, with the control on top of the petrol tank. Douglas machines became very popular because of their lightness, ease of starting and speed: in the 1912 Junior TT races Douglas took first, second and fourth places.
In the First World War thousands of 2 ¾ HP machines were commissioned for use by despatch riders and performed splendidly.
In 1915 a 596 cc model was introduced to cater for the need for a more powerful sidecar puller.
A notable difference in engine design with the 2 ¾ HP model is the wet sump oiling system.
A year later the 4 HP model was 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, many small engine design improvements.
To sum it up: quite another machine! Between 1916 and 1921 hardly any changes were made.
At the 1921 Olympia Show the company remarked: “ The 4HP 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 disappeared from the range in 1924.
Bore x stroke are 74.5 x 68 mm, petrol capacity 9 litres, oil capacity 4 litres.
Petrol consumption is given as circa 1 litre per 25 kilometres and the machine weighs 120 kgs.
This finely restored and well running machine comes complete with Acetylene head lighting.