The Beaulieu Autojumble always will cough up a few mysteries. This time best of show in that respect was the engine Yesterdays (antique Motorcycles) put up for display. An extremely well engineered one cylinder, approximately two and a half feet high. The Yesterday people think it was created around 1910 yet the machine is ultimately modern in many respects so anything is possible. Let's start with the basics. The single cylinder for breathing has four desmodromic valves and a compressing unit getting the umpf from sub-piston pressure, and regulated by the bevel axle which also drives valvetrain and ignition. The twin ignition feeds four sparkplugs. You can find more pictures HERE and a video of the engine being turned HERE.
Ok, now where would one need a set-up like this car (Voiturette racing machine? Racing boat?) Except for a few below 10 digits the engine has no markings at all. Possibly it is a prototype or demonstration machine. The machine is showing strong family resemblances with the 1910 Lion-Peugeot Evolution long stroke vertical twin as shown in Kent Karslakes's book Racing Voiturettes. Maybe a one cylinder study on the same theme?
Over to you...