Designed by the legendary Edward Turner, the Ariel Square Four was first shown at Olympia in 1930. Unique at the time of its introduction, the 'Squariel', as it was swiftly dubbed, featured a single block of four cylinders and twin geared-together crankshafts with pistons phased at 180 degrees. The crankcase was split horizontally, unusually for a motorcycle engine of the period, while the vertical valves were operated by a single overhead camshaft. A supercharged example was raced at the Isle of Man TT in 1931 without success, which was hardly surprising as its makers had envisaged the model as more of a luxury tourer than an out-and-out sports machine.
Although launched as a '500', the Squariel was soon enlarged to 601cc with an eye on the important sidecar market, this bigger version being made available for the 1932 model year. In 1937 a total redesign saw it re-emerge as the Model 4G, with 995cc overhead-valve engine, making the Squariel an even more enticing prospect for sidecarists. There was also a 599cc 4F version of this new pushrod Square Four, most of these smaller models being earmarked for export. It is estimated that some 400 examples of the 4F were made.
This restored example of the rare '600' Square Four benefits from recently installed new pistons and an overhauled magneto. Offered from a private collection comprised entirely of Ariel motorcycles, the machine was recently registered in France and comes with French Carte Grise.