Strange Motorcycle Engines

Stranger than Spagthorpe

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The Granville Bradshaw Omega

Late in 1955, came the Omega engine, which was of a rotary form, ingenious and most unusual. It was difficult to see how it worked at all, but the design was intended to reduce the inertial loadings of the conventional layout.

The design was based on an annular cylinder, formed from two light-alloy castings bolted together. Within these was formed a toroidal chamber, which can be likened to an inner tube or an O-ring, being a ring with a round cross- section.

For the Omega, the working surface was hard chrome plated and within it were four double- ended pistons with rings at each end and a shape to match the toroid. Each opposing pair was joined by a cross-link, and each of these was bolted to one of two concentric shafts. These each had a short arm at the other end, with a connecting rod to join that to a 180-degree, two- throw crankshaft.

As this turned, the links caused the pistons to move some 30 degrees back and forth, so the space between the opposing crowns varied. If this was not enough, the entire cylinder also rotated at half crankshaft speed and was driven from this by helical gears. In its sides were cut inlet and exhaust ports, and the single sparking plug was screwed into the side. Lubrication was by petroil, with a separate system for the crankshaft, and cooling was by fins on the toroid and enclosure to guide the air.

The Omega was the final fling of a man whose ideas were always clever and innovative, but who sadly failed to understand the commercial needs of the business. His designs were novel, but invariably costly and seldom trouble-free, so his long involvement with the industry made news and kept everyone intrigued, rather than pro- ducing machines for riding. Without such men, the world would be the poorer.

Roy Bacon 1989