The Ariel Motorcycle Company was founded in 1902, borne out of the earlier bicycle business. The name Ariel originally comes from their ultra-light first penny-farthing bicycle. For its life as a motorcycle manufacturer, the company was based at Dawlish Road, Bournbrook, near Selly Oak, Birmingham. In 1944 the business was sold to BSA, who maintained production at Bournbrook until moving it to their Small Heath factory, the last true Ariel motorcycle being produced in 1967. Two Ariel engines are referenced in period.

The Ariel Red Hunter
Developed in 1932, the Red Hunter was the mainstay of the company – becoming famed for their reliability (every engine was tested for at least two hours before being used). It was a single cylinder engine produced in a range of sizes, topping out at the magical 500cc. The engine was very similar to others singles of the era, being pushrod-operated twin valve, air-cooled. A tell-tale is the polished steel cam covers. Power output on pump fuel was about 25bhp, somewhat low compared to a similar JAP. Like the JAP, output was to a separate gearbox.
A variant of the Red Hunter motorcycle would be a mainstay of the Army through the Second World War. It would also be popular with grasstrack racers and trials riders, but it never really made a mark in 500s.

Red Hunter mounted in the rear of the Wenz American special. Photo courtesy Bob Wenz

The Ariel Square Four
The Square Four (sometimes nicknamed the Squariel) was developed in 1928 as that rare beast for the time, a four-cylinder motorcycle engine. However, rather than the expected in-line layout, it was in fact more of a pair of twins, merged into a single unit, with a central flywheel and a single cylinder head. From above, the four cylinders formed a square (hence the name), with a small exhaust manifold (for the forward and rear cylinder) on each side of the cylinder head.

The original engine was a 500, with chain-driven overhead valves. But by 1937 a 996cc version was produced. The versions most likely used in competition were the 1949 redesign, which introduced alloy head and barrels, giving 35bhp on pump fuel in standard specification, or the 1953 Mk II (also known as the four-pipe as the exhaust manifolds were replaced with separate pipes) which increased power to 40bhp

Neither engine could really hold a candle to readily available and  JAP alternatives, and there was insufficient incentive to undertake the development work necessary to be competitive. Ken Neve used a modified engine in his KN II, Whitby had one in the GSW but changed to JAP and Bob Wenz used a Red Hunter to create the first American built car