Ariel Square Four 1000
Few motorcycle models are as unusual as Ariel's 4-cylinder Square Four, the motorcycle that was a curiosity in its time, and the result of Edward Turner's brilliant engineering brain.
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Rumor has it that the Square Four engine was conceived over a pint in a pub basement in London in the 1920s on a drawing pad, signed by Edward Turner himself, one of the most prominent figures in the English motorcycle industry. Turner achieved the title of Sir, for his efforts in a motorcycle industry that was a world leader until the 1960s. The four-cylinder four actually resembled an engine where two parallel twins were mounted one behind the other. The closest thing that posterity has come to this strange construction is Suzuki's street racer RG500Gamma, where the pistons are also placed in a square.
Rejected by BSA , realized by Ariel
The first Square Four model was shown to the press in the autumn of 1930. It had a displacement of 500 cc and was called the 4F. The man behind the design was the then young and unknown engineer Edward Turner. Turner's sketch was one of several ideas the young man was working on, and it was first shown BSA . They rejected the project after a brief review of Turner's sketches. However, this did not mean that the idea of a “square four” was dead. Barely two years later, young Mr. Edward's idea materialized thanks to Jack Sangster and Val Page taking an interest in the design. Both were key figures in the management of Ariel , and they were convinced by the young man's undeniable talent, and employed Turner in 1928. The first model, the 4F, went on sale in 1931, and was produced until 1936. The 4F changed little, with the exception of the engine, which was upgraded to 600 cc in 1932. The Square Four engine was a tough affair, and often preferred by sidecar riders because of its solid torque. The weakness, however, was overheating of the two rear cylinders.
997 cc
This led to the development of a new 997cc four-cylinder, the 4G model, in 1936. A number of improvements now helped to cope with the heat build-up. For Ariel , the Square Four remained the top model in the sales brochures right up until the last model in 1959. By then, the Birmingham factory had produced a total of 15,639 units of the three versions, which were 500cc, 600cc and 1,000cc.
Technical data Ariel Square Four 1000 MKII, 1953 model:
Engine: 4-cylinder 4-stroke, OHV
Displacement: 997 cc
Compression: 7.2:1
Power: 45 hp at 5500 rpm.
No. of gears: 4
Front tires: 3.25x19
Rear tires: 4.00x18
Tank: 23 liters
Weight: 197 kg (dry)
Top speed: 160 km/h
