350 cc Single Overhead Cam and Twin opposed rotary valve 750 cc valve

I was working in my workshop one friday afternoon and this young man came in, in boardshorts and t-shirt…. his name was Steve Cohen.  In the 70’s and 80’s his father and himself were manufacturing hang-gliders …. pioneers at the time.

At the time I was building a 125 watercooled twin cammed, 4 valve engine ….. Steve asked me would I be able to help him by building an engine, he wanted to build an Ultralight Aeroplane, at that time he was a fresh entrepreneur.  I agreed and started building an engine, the engine had to be very light, rev no faster than 2000 revs with 120 pounds of thrust.

So I built this little 350cc single overhead cam… basic … made a test jig in the yard, a 3 wheeler with a stand for the engine with a spring balance, by now Steve had this Bi-plane built, he had another gentleman from Dehavilland helping who was an aircraft builder.  The engine was ready… and bloody hell…. I watched it take off and fly around the sky… the plane was far to heavy for the engine, but it put Steve on the journey he is on today with Ultralight.

I started off to build a more powerful engine, smaller and lighter, which was the 665 cc rotary valve, the valve serviced both cylinders and also held the prop, so that the prop run half engine speed cause it was bolted to the rotary valve in the centre which enabled the motor to rev at half speed.  The prop was bolted to the crankshaft.