Blown SW Douglas Motorcycle

[Dave]

Brian sent in this photo and note about a supercharged Douglas.

Herewith a real flyer, I would suggest. In my researches for the Aero Engine Book, I came across this supercharged Douglas which had been supposed to be "a Rotary Valve experiment on a vee-twin".

Clearly, the drive to the "rear cylinder" is the standard primary-drive and the other chain drive, to a mirror-image position above the front cylinder, is to a ??? supercharger. I have disabused the photo-provider about the vee-twin notion. There appears to be something like a boost gauge on the steering damper link also. No other info but thought it would be of interest. Any info from our membership would be interesting.

I had hoped it was going to be the engine that I have William Douglas Ltd drawings of, which was 1934 500cc water-cooled rotary valve with bevel gear drive. I intend to produce a readable drawing from the faint G.A. sketches and proper manufacturing detail drawings of the gears etc.
I have had to do this for the Book in the case of the Elf 1.5 litre twin V-4/V-6 and V-8.
Meantime I will endeavour to trace more info on this blown projectile.

Best Wishes

Brian Thorby

[Doug]

The bike was built by Mr Reid of Birmingham circa 1937. The blower is a Centric, Type 125A, fed by a TT Amal on the RH side between the gearbox and magneto. You can see the pipe leading from it to the blower, where it crosses in front of the magneto. Boost was limited to 8lb*in^2. The pale color of the heads is due to an 'aluminized' finish to both them and the cylinders. Details via Oct 28th issue of The Motor Cycle.

-Doug