ARIEL

600 Type 4F I Square Four – 1932

Edward Turner, who began his career at Ariel in 1928, was a young engineer who dreamed of sweeping the obsolete single-cylinder motorcycle off the streets once and for all.

Forming a Square

Scorning the inline four-cylinder engine as too long, whether installed longitudinally or transversely, he had the original idea of placing four cylinders in a square formation.

A Good-but Complex-Idea

The result was an engine that, despite its complexity, was compact and well-balanced. Two V-twins were joined together by helical gearing on their flywheels (their crankshafts were overhung, except for the left rear shaft, which carried the primary drive sprocket). They revolved in opposite directions, firing diagonally to give excellent balance with minimal vibration. The Ariel 500 Four's technological skills made it the star of the 1930 London Show. But the costly 500 suffered from over-hasty development and a poor power-to-weight ratio. It was bored out to 600cc in 1932. But the rear cylinders overheated, the cylinder head joint failed and the engine leaked oil and was noisy. In 1935, Ariel revised its design and created the Four cylinders in tandem 1000cc Square Four, which developed 10 hp more than the 600 Type 4F and attempted to correct its failings. The crankshaft gearing was moved to the side and pushrods and rockers between the cylinders replaced the overhead-camshaft. The horizontal crankcase joint became vertical and the forward-mounted Amal carburetor was replaced by an automobile-type Solex at the rear.

SPECIFICATIONS

Engine: 597cc (56x61mm) air-cooled square-four four-stroke; two crankshafts geared together in tandem at 180-degree offset

Power Rating: 24 hp @ 6000 rpm

Valves: single chain-driven overhead-camshaft; two vertical valves per cylinder

Fuel System: Amal carburettor

Transmission: 4-speed, chain final drive

Suspension: girder forks (front); rigid (rear)

Brakes: drum (front & rear)

Wheels: 19 inch (front & rear)

Weight: 370 lb (subsequently 409 lb)

Maximum Speed: 100 mph

The 1932 version used the double-cradle frame of the 500 Sloper, while the 1936 model had a single front downtube.