Prewar Douglas motorcycles – Dating information with Engine, Frame and Gearbox numbers for the 3-1/2HP and 4HP Models, from 1914 to 1923.
Demand for larger bikes than the original 2-3/4hp model.
WW1 created an increased demand for more power. The motorcycles were needed to pull sidecars and carry extra weight through difficult terrain. Douglas’ answer was to produce the 500cc (3-1/2hp) and 600cc (4hp) models. These motorcycles were all side valve machines,. The early ones were used for wartime service. Civilian production continued until February 1917, when it ceased for the final year of the Great War.
For some images and model information on all prewar motorcycles, visit the full range of Douglas models information page.
| Year | Frame # | Engine # | Gearbox # / letters | Distinguishing features for the year / model |
|---|---|---|---|---|
| 1914 | 1001(?) -1888 | 1001(?) -1888 | 1001(?) -1888 | Used for wartime service and for sidecar work – look for distinguishing khaki paint or for signs of having pulled a chair – clamp/bolt marks, or even a bent frame. Cataloged as Model A and B (not to be confused with 2-3/4hp of 1907-08.) Physically larger engine, 68 x 68mm, horizontally divided crankcase. Sitting on a large base the fore part recognizable as an oil sump. Consequently no oil compartment in the petrol tank. Chain to 2-speed countershaft unit behind engine with cone clutch, thence belt to rear wheel. Model A, foot rests, no clutch. Model B, foot boards, clutch and kick start. Bifurcated twin front down tube frame, these tubes have ‘D’ shaped cross-section (conventional round tubes on later models.) Braced headstock. Rear brake block works on outside of belt rim (into V-groove.) |
| 1915 | 1897-2647 | 1897-2647 | 1897-2647 | Larger 4hp model introduced, 74 x 68mm. Bosch magnetos unavailable due to war. American Dixie followed by CAV substituted. |
| 1916 | 2654-3794 | 2654-3794 | 2654-3794 | 3-1/2hp discontinued and A & B designations taken over by 4hp. Model A with 3-speed and clutch. Model B with same specs. Possibly there is a typo in the catalog and the A was still 2-speed. Archimedean screw oil pump replaced by rotary vane pump with auxiliary drip sight on petrol tank (all oil is still carried in the sump.) Offered also with sidecar. All welded front fork blade of lighter design similar to 2-3/4hp of same year, replacing a welded-brazed lug fork used previously. Primarily EIC magnetos used from this point on. Rear brake block now operates on inside of belt rim. |
| 1917 | 3803-4756 | 3803-4756 | 3803-4756 | |
| 1918 | 5314-7210 | 5314-7210 | G4/****(3-speed) | As a result of the utilization of engines for other purposes, stationary generators, etc. the numbering system is not very rational. |
| 1919 | 7233-9988 | 7233-9988 | G4/****(3-speed) | Headstock no longer braced. |
| 1920 | 9987-13050 | 9987-13050 | G4/, G7/ (multi-plate) | Introduction of dry multi-plate clutch on gearbox. Model B20. |
| 1921 | 13051-13600 | 13051-13600 | G4/, G7/ (multi-plate), G11/ | Model B21. |
| 1922 | 13601-14280 | 13601-14280 | G4/, G7/ (multi-plate), G11/ | Detachable cylinder heads with valve ports integral. Telescopic filler neck for oil sump. All lug brazed front fork. All chain drive version offered with sidecar outfit. |
| 1923 | 14281-14713 | 14281-14713 | G4/, G7/ (multi-plate), G11/ | Heated muff on intake manifold. Model B, solo, still belt drive. Model 4HC (sidecar), all chain drive. Model discontinued in favor of big OHV twins with sidecar the following year. |
Credit: Thanks to Doug “K” for his kind permission to reproduce this hard work that he and Doug “C’ compiled many years back. It is reproduced on this page with his permission and the acknowledgement of The Douglas Forum.
Looking for dating information for the Douglas 2-3/4 HP models? Go to the Prewar Douglas 2-3/4 motorcycles – Dating information Engine, Frame, Gearbox numbers
If you have a prewar Douglas motorcycle, please join the London Douglas Motorcycle Club. It is available to everyone; owners and non-owners in any Country.
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Disclaimer: The information supplied here is a guide. It’s pretty accurate, but should be used as a guide only.
