The Royal Ariel Square Four

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1953 was the first year for the Square Four to have separate exhaust pipes.
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Non-stock oil cooler (just visible above left exhaust header) keeps things cool.
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Like many touring bikes (Honda’s Gold Wing comes to mind), the original Square Four was designed with performance in mind.
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By the time the Square Four was due for production, the financial collapse of 1929 had initiated the Great Depression, and Sangster demanded changes to make the Square Four easier and cheaper to produce.
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The 4G’s final upgrade came in 1953 with the introduction of the MkII, featuring a new cylinder head with four separate exhaust headers.
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The Anstey link was intended to maintain constant chain tension by allowing the wheel to move through an arc.
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Square engine configuration keeps the Ariel looking almost svelte.
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Owner Joe Block rides his Square Four regularly.
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"It has great low-down torque, so you don’t really need to shift the gears. You can be down to 10-15mph in top and pull away," Joe Block says.

1953 Ariel 4G MKII Square Four
Claimed power: 45 hp @ 5,500 rpm
Top speed: 100 mph
Engine: 997cc air-cooled OHV “square” four, 65mm x 75mm bore and stroke, 7.2:1 compression ratio
Weight: 425 lb.
Fuel Capacity/MPG: 6 ga. (22.7 ltr.)
Price then/now: $950 (est.)/$15,000-$25,000 

Ariel Square Four owners are used to being quizzed about the unique cylinder arrangement enjoyed by their air-cooled engines, the question most often posed being, “Don’t the rear cylinders overheat?” Savvy “Squariel” owners are ready with the answer. “Yes, but when they do that, we put them on the front …”

Although the limitations of Edward Turner’s compact power unit were recognized fairly early on in its life, it was still good enough to remain in production for 28 years, longer than many more famous designs. When Ariel owner BSA Group pulled the plug in 1959, the Square Four had become a rather portly touring machine that, though still capable of relatively high speeds, was being outclassed in the performance and handling stakes by newer British 650cc twins. But it wasn’t always that way. Like many touring bikes (Honda’s Gold Wing comes to mind), the original Square Four was designed with performance in mind.

Page and Turner

In 1928, Edward Turner was a motorcycle dealer in Peckham, London, with a dream of manufacturing bikes of his own. He had already designed and built two versions of the 500cc single-cylinder “Turner Special,” the first with a gear-driven overhead camshaft and the second using a vertical bevel-drive shaft and face cam to operate the valves.

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