The 4hp Douglas was introduced in 1915 in response to a demand for larger machines to haul sidecars. The 596cc side-valve, flat-twin drivetrain resulted in a versatile and reliable motorcycle that had plenty of power for arduous and demanding environments. It was for this reason many 4hps were used to aid troops in WWI.
The mechanics were ‘state of the art’ for the time – the bike carried the oil in the sump (which had a small inspection window) which was then recirculated into the bearings and cylinders. The majority of bikes up to the era had a tank that shared fuel and oil; however the novel Douglas design allowed for a standalone fuel tank, with more capacity and an enhanced range. Genius!
A respected amateur rider and diarist of the era, the Rev Basil Davies (a.k.a Ixion to his followers) wrote about the 4hp:-
“I bought my machine for solo work,” Ixion reported, “and have been charmed by the ease with which it responds to its kick-starter, in which respect it easily excels and single-cylinder I have owned.”
Photo Credit: Andrew Butler
Ixion seemed impressed with the lubrication system:
“The oil is carried in a sump which is an extension of the crank case, no oil being carried in the tank, which is reserved for petrol only. The method of lubrication is very simple and effective, as well as being practically fool proof. When the oil is placed in the sump beneath the crank case the rider can dismiss the question of lubrication from his mind until he has travelled 500 miles or so, but it is better to add a little oil at more frequent intervals…The oil is raised from the sump by an elevator on the Archimedean screw principle to troughs into which the big ends dip. These throw the oil into the cylinders, whence channels convey it to the other bearings. The surplus drains back through a filter composed of two gauzes into the reservoir for future use…”
Ixion described the ride and comparison to the smaller, popular 2¾hp model as follows:
“Acceleration is quite a unique feature; the engine is much better silenced than the 2¾hp of the same make, whilst retaining its balance—in fact, I think its balance is better, and, excluding very low rates of revolution, for which I have not yet tuned it up to my satisfaction, the running is more reminiscent of a steam turbine than any motor cycle engine I have yet handled. Increasing wind pressure on the cheeks is the most pronounced sensation as the throttle is opened…”
The 4hp continued to be produced post-WWI and its achievement in the war helped boost sales. At the 1921 Olympia Show, Douglas advertised the model using the wartime success as a footstool:
“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”.
an article by The Girder Club
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