Edward Turner would go on to fame and acclaim as designer of one of the world's great motorcycles, the 1938 Triumph Speed Twin, but 10 years earlier he was a frustrated young man. Tucked under his arm were blueprints for a unique engine, yet no British factory would give him the time of day. Ariel, just coming out of bankruptcy and looking to make a splash, listened to Turner. So was born the Ariel Square Four, a landmark design that would remain in production for the next three decades.

After 18 months of intense R&D, the first Square Four rolled off the production line in 1931. That original 500cc engine was in essence two parallel-twins situated one behind the other to form a square configuration. Each pair of pistons had its own counter-rotating crankshaft geared to the other. Valve actuation was by chain-driven overhead camshaft, a very advanced feature in those days of pushrod valvetrains. In response to sidecar owners, displacement grew to 600cc in 1932, but even at that the rear two cylinders often ran hot. The answer in 1936 was the iron-barrel G-model, a complete redesign with the motor growing both physically and on the spec page to 997cc. Gone was the overhead cam, replaced by pushrods.

The result was "The Monarch of Multi's," a very handsome motorcycle, as illustrated by this restored 1950 example from the Capt. Eddie Rickenbacker bar.