The only 3 bikes with radial engine Ever Built

Dave B An often overlooked important difference between a radial engine
and a rotary is the fuel and ignition systems. On a radial the carburetor feeds the cylinders as on any modern piston engine, with a intake ring, which is a manifold- and an intake valve.

This isn't possible with a rotary engine because the carburetor would be spinning along with the cylinders. So a rotary engine has a specialized fuel inlet at the bottom of the cylinder which feeds the fuel air mix through the crankcase. Some rotary engines have only an exhaust valve such as the gnome Monosoupape aircraft engine, where fuel enters through a bottom port. All radials use an intake valve and an exhaust valve, a stationary carburetor and can be throttled. A rotary also has no throttle and its speed is controlled by either the load itself or an ignition cut out.

  Non Sibi Sed Patriae Remember that rotary engines, i.e., engines that rotate ABOUT the crank shaft (NOT radial or inline engines that remain stationary while the crankshaft rotates as in modern engines), were the principal engine employed in many First World War military aircraft used by both sides.

So, in the years after the war, these engines were plentiful (and likely cheap) and well-understood. They were lighter and ran cooler that radial and inline engines. It's a wonderfully creative idea.

  Steve po You are correct. Stationary crankshaft radial engines were known as rotaries. No one of the era would have confused them with a Wankel rotary, since those wouldn't be invented for another 40 or so years, so they just called them rotaries back then. Besides, the Mazda rotary shouldn't have even been called a rotary since its more of a planetary action anyways.

Joseph Stalin The Megola has a rotary engine, not a radial. They're very similar, but in rotary engines the pistons rotate around a stationary crankshaft, while a radial engine has fixed pistons and a rotating crankshaft. And a Wankel Rotary is something else altogether, it has no pistons and is the one used in the Mazda RX series.  Wankel's original design was pure rotary motion (like a turbine) and he never really accepted the orbital/planetary design that became mass produced by many manufacturers years later.

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