The Royal Ariel Square Four

In production for 28 years, the Ariel Square Four became a comfortable touring motorcycle in its later days.

| March/April 2013

  • Exhaust
    1953 was the first year for the Square Four to have separate exhaust pipes.
    Photo By Jeff Barger
  • Oil cooler
    Non-stock oil cooler (just visible above left exhaust header) keeps things cool.
    Photo By Jeff Barger
  • Ariel Square Four
    Like many touring bikes (Honda’s Gold Wing comes to mind), the original Square Four was designed with performance in mind.
    Photo By Jeff Barger
  • Side of Suare Four
    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.
    Photo By Jeff Barger
  • Royal Square: 1953 Ariel Square Four
    The 4G’s final upgrade came in 1953 with the introduction of the MkII, featuring a new cylinder head with four separate exhaust headers.
    Photo By Jeff Barger
  • Chain tension
    The Anstey link was intended to maintain constant chain tension by allowing the wheel to move through an arc.
    Photo By Jeff Barger
  • Ariel front end
    Square engine configuration keeps the Ariel looking almost svelte.
    Photo By Jeff Barger
  • Joe Block
    Owner Joe Block rides his Square Four regularly.
    Photo By Jeff Barger
  • Back
    "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.
    Photo By Jeff Barger

  • Exhaust
  • Oil cooler
  • Ariel Square Four
  • Side of Suare Four
  • Royal Square: 1953 Ariel Square Four
  • Chain tension
  • Ariel front end
  • Joe Block
  • Back

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.



In his attempts to find a manufacturer among Britain’s bike makers, Turner fetched up at the offices of Ariel Works Limited in Birmingham, where, instead of taking on Turner’s special, they offered him a job in the design department working under Valentine Page. What had impressed Ariel boss Jack Sangster was Turner’s second design, a unique 4-cylinder sketched out, goes the legend, on the back of a pack of cigarettes. (It’s likely Turner had already produced engineering drawings, but the smoke-pack story has stuck.)

Turner’s creation bristled with fresh ideas and ingenuity. The 4-cylinder 500cc engine used two crankshafts connected by helical gears with a chain-driven overhead camshaft. The cranks were transversely mounted, with one set in front of the other and each crankshaft driving a set of two pistons. The pistons were literally in a “Square Four” arrangement. The rear crankshaft’s helical gear also transferred power to the integral 3-speed transmission.



The sound and the fury: celebrate the machines that changed the world!

Motorcycle Classics JulAug 16Motorcycle Classics is America's premier magazine for collectors and enthusiasts, dreamers and restorers, newcomers and life long motorheads who love the sound and the beauty of classic bikes. Every issue  delivers exciting and evocative articles and photographs of the most brilliant, unusual and popular motorcycles ever made!

Save Even More Money with our RALLY-RATE plan!

Pay now with a credit card and take advantage of our RALLY-RATE automatic renewal savings plan. You save an additional $4.95 and get 6 issues of Motorcycle Classics for only $24.95 (USA only).

Or, Bill Me Later and I'll pay just $29.95 for a one year subscription!




Facebook Pinterest Instagram YouTube Twitter

Free Product Information Classifieds