Ariel Motorcycles Square four MkII (1956)
Vehicle descriptionClassic British motorcycle. The Square Four is a motorcycle produced by Ariel between 1931 and 1959. The early engine with "two transverse crankshafts" was essentially a pair of 'across frame' OHC parallel twins joined by their geared central flywheels, with a four-cylinder block (or Monobloc) and single head. The idea for the engine was rejected by BSA, but adopted by Ariel. Thus it became the Ariel Square Four. In 1953, the 'four pipe' 997 cc Ariel Square Four Mk II was released, with separate barrels, a re-designed cylinder head with four separate exhaust pipes from two cast-aluminium manifolds and a rocker-box combined with the inlet manifold. A redesigned frame provided clearance for the high-mounted, tall, car-type, SU carburettor. This 40 hp (30 kW) Square Four was capable of 100 mph (160 km/h). It weighed425 lb (193 kg) and cost £336.16.6. In 1954, Ariel built prototypes of a Mk3 with Earles forks, but the model was never put into production. In 1959, Square Four production, along with that of all other Ariel four-stroke models, ceased.
|Engine:||997 cc, 4-stroke, square four, air-cooled, OHV, 8-valve|