ARIEL SQUARE FOUR
Ariel’s sophisticated Square Four turns 90 this year
A celebration of the veteran superbike on its 90th birthday
Honda’s CB750 four was loudly celebrated on its 50th birthday last year. But, while the Honda might be able to claim that it brought four-cylinder motorcycling to the masses, it was more than 40 years behind Ariel’s Square Four, which enjoys its 90th anniversary this year.
It was Edward Turner, whose name would later become synonymous with Triumph, who designed the original Square Four. In the late 1920s, having run Chepstow Motors in Peckham Road, south London for some time, Turner was on the lookout for opportunities within the motorcycle industry. He had already built a machine featuring his own design of 350cc overhead-cam engine when he drew up an ohc 500cc four-cylinder engine in 1928. Offering the design to BSA, he was rejected – but Ariel were considerably keener on the idea and took on Turner to help bring his brainchild to production.
Effectively, the design comprised two parallel twins with the crankshafts geared together and running in a common crankcase. There was chain drive to an overhead camshaft and fully enclosed valve gear – a thoroughly modern unit for its time. A four-speed Burman gearbox with hand change was fitted (despite Turner’s original design featuring a gearbox in unit with the engine) and by 1930 the first Ariel Square Four was ready to astound the public at the Earls Court Show.
The first model, the 498cc 4F with its rigid, duplex frame and girder forks, ran for just a year before being joined by a 600cc version in 1932. Two years later, both models benefitted from a new single-down tube frame and a switch to foot gear change – but in 1936 there was a much more significant evolutionary step with an all-new ohv 995cc engine replacing Turner’s original unit. A 600cc 4F ohv model joined the line-up in 1939, too, before the outbreak of World War II temporarily halted production.
After the war, manufacture of the larger four (the 4G) resumed, but the 600 was dropped. The 4G, which had undergone only relatively minor revisions since 1936, gave way to the 4G MKI in 1949. The new model featured an all-alloy engine with two exhaust pipes and would prove to be the penultimate development of Ariel’s four. The final version was the 1953 MKII, with a redesigned cylinder head and four exhaust pipes. Production of the Square Four finally ended in 1959, when Ariel abandoned
production of all their four-stroke machines to concentrate on the two-stroke Leader and Arrow models.
With a total of just 15,639 Square Fours (of all types) manufactured over a 19 year production run (with six years out for the war), the ‘Squariel’ can hardly claim to be a machine for the masses like the Honda four. But, as an innovation, it surely merits equal attention. And a Square Four would certainly have been a thing of wonder back in 1930. That alone makes it a bike worth celebrating. The bare specification – the four cylinders in a world of singles, the overhead camshaft in an ocean of ohv and side-valves – the Square Four was simply a revelation.
Despite its advanced specification, though, the Square Four was never intended as a sporting mount. Turner’s design was intended as a sophisticated tourer. And the promotional fanfare surrounding the bike’s launch reflected that. First, there was the almost obligatory tilt at winning the Maudes Trophy for 1931, awarded for feats of endurance by production machines. The number seven was the theme of the challenge and the Square Four romped all seven of the tests thrown at it, which were:
• A seven-hour endurance run at Brooklands – 368 miles covered in total.
• Fuel and oil consumption test: approximately 700 miles on seven shillings’ worth of petrol and oil.
• Cylinder head decarbonised in four minutes 19 seconds using only spanners from the motorcycle’s tool kit – target time: under seven minutes.
• A one-hour speed run at Brooklands. More than 80 miles covered – target 70 miles.
• Being run for 70 minutes in each of its four gears on public roads.
• Seven non-stop ascents and descents of each of seven famous test hills: Porlock, Lynton, Beggar’s Roost,
Countisbury, Bwlch y Groes, Dinas Hill and Alt y Bady.
• Covering 700 miles in less than 670 minutes – target time: 700 minutes.
It was an impressive showing by the new four and, if that wasn’t enough, Ariel dreamed up another stunt – getting seven schoolboys to each try to kickstart a Square Four seven times in succession. Out of 49 attempts, the Ariel started first kick 48 times. Try that with a Velocette Venom.
Although the Square Four was never intended as a racer, its performance potential was amply demonstrated in 1933, by racer Ben Bickell. On his (modified and supercharged) machine he recorded a 110mph lap at Brooklands.
Over the last 90 years, the Square Four has retained it popularity – and mystique. These days, the Square Four – in any of its various incarnations – has become a very desirable classic machine. You’d need to pay anywhere between £12,000 and £18,000 for a MKI or MKII model and more for a an early example. There’s an unrestored 1931 4F 500 that’s been in one family ownership since new being advertised for £29,500 currently, for example. And the enduring popularity of the Square Four – together with an excellent owners club and specialist parts supplier Draganfly – mean that the spares situation is pretty good, too.
By post-war standards, the first 500 and 600cc models lack a little power. They do run rather hot, too, giving their magnetos a torrid time. But they are compact, reasonably agile and delightfully smooth. The ohv 600s feel a little under-gunned, too – perhaps unsurprisingly as they are in essence a sleeved-down 1000. For practicality, the late, alloy-engined 1000s – especially the MKII – are the best bet. They offer 65mph cruising, suffer far less than the earlier iron-head models from overheating issues and boast all the strut and swagger of a four.
And that’s really what the Square Four was all about from the start – sophistication, smoothness and effortless power, rather than out and out performance. Ninety years on, a good one will still deliver just that.
‘SEVEN SCHOOLBOYS TRIED TO KICKSTART A SQUARE FOUR SEVEN TIMES. OUT OF 49 TRIES, IT STARTED FIRST KICK 48 TIMES’