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Ariel Square Four Gallery

The Square Four, introduced in 500cc form during 1931 was the work of Edward Turner. Conceived as a luxury tourer it utilised a chain driven over camshaft and four cranks with the gearbox being driven by the rear left hand example. The new model was joined by a 601cc variant the following year which eventually replaced the smaller machine. Unfortunately for Ariel, the introduction of complex, luxury model into an already crowded market place at the height of a recession resulted in limited sales, many admired the machine but those that could afford a luxury mount tended to opt for the known qualities of one of the large capacity vee twins, consequently examples of either over head cam model are rare. More Ariel Square Four information.

Bike Image Description
Ariel Square Four Ariel Square Four
  • Engine - 997cc, OHV, square four
  • Top Speed - 100mph
  • Horsepower - 42bhp @ 5800rpm
  • Transmission - 4-speed
  • Frame - tubular single loop
  • Brakes - drum/drum
  • 1932 Ariel 600cc Square Four 1932 Ariel 600cc Square Four One of Ariel's most notable engines was the Square Four, the first prototype emerging in 1930. As the name suggests, the cylinders were configured with two cylinders directly behind the front two cylinders. Starting as a 500cc engine, then increased to 600cc and finally the 1000cc configuration. The 'Squariel' was plagued with heat problems as one might imagine having two cylinders directly behind the front pair. Despite the heat issues it remained in production until 1954.
    1933 Ariel Square Four Race, 500cc 1933 Ariel Square Four Race, 500cc  
    1934 Ariel Square Four
    Ariel Square Four

    1934 601cc version, has been in the same family ownership for over fifty years. The machine was purchased by the present owners father for £15 and she recollects being a pillion on the machine during the 1950's. A comprehensive restoration was carried out during 1996 at which time new main roller bearings, big ends and pistons were fitted. The mag/dyno was rewound and the wheels were rebuilt with new tyres being fitted. Items such as the chains, cables and battery were replaced as a matter of course and new wiring was installed. The chrome tank and black and gold paintwork are described as being in "as new" condition as are the cycle parts and electrics. The engine is described as having had a "total rebuild" and the transmission is described as being in good working order.

    Won the "Best Pre-war Bike award" in the 1996 Festival of 1000 Bikes concours competition following her restoration and was subsequently placed on display at RAF Manston, nestling under the wing of a Hawker Hurricane, as an example of an RAF pilots wartime transport. Image provided by

    1939 Ariel Square Four 1939 Ariel Square Four  
    1952 Ariel Square Four Combination
    Ariel Square Four

    When "The Motor Cycle" tested an example of the Ariel Square Four Mark II in April 1953 they found that the machine was capable of just shy of 100 mph describing it as being "a unique high-performance mount with gentle manners and outstanding acceleration" resulting from twenty years of development. The Square Four had been conceived by Edward Turner during his time at Selly Oak and was introduced as a 500cc, soon to be increased to 600cc over head cam design in 1931.

    However the early engine suffered from a weak and insufficiently cooled cylinder head prone to blowing its head gasket. Edward Turner consequently developed a new 997cc over head valve engine retaining the name and layout, but little else for the 1936 season. The new engine, typed the 4G provided the basis for all Square Four production until 1948 when it was joined by the Mark II "alloy engine", which featured an alloy barrel and head in place of the iron units previously employed. Equipped with telescopic forks and "Anstey" link rear suspension, the Square Four provided the discerning rider with a luxurious mount capable of covering long distances at high speed in comfort in either solo form, or as with this example, attached to a sidecar, surpassed only by the twins emanating from Stevenage.

    1952 Ariel Square Four
    1952 Ariel Square Four

    Ariel replaced the cammy 600cc Square Four with an overhead valve design displacing 997cc during 1936. The redesigned engine retained the geared twin crankshafts first seen in the overhead cam engine, although the gears had moved to the left hand side of the engine, but little else, other than the name, remained unchanged from the cammy Square Four. 1939 saw the introduction of a compensated-link, plunger equipped frame which continued in use, complimented at the front by Ariel telescopic forks, when production of the 4G Mark 1 resumed in 1946. The model continued with very little change for the next two years, until in late1948 a redesign took place, resulting in a new version equipped with an all alloy engine. The redesign was well timed as the Square Four had been putting on weight as a result of the increased specification, the alloy engine and other measures resulting in a saving of approximately 100lbs over the iron engined version.

    Image provided by

    1953 Ariel Square Four Mark II 1953 Ariel Square Four Mark II Introduced in 1953, the 'four-pipe' MkII with re-designed cylinder head was a genuine 100mph machine. With its limitless reserves of pulling power and innate smoothness, the model was always a favourite of the sidecar brigade.
    1953 Ariel Square Four 1953 Ariel Square Four Ariel Square 4 Mk 2 - four pipe. This is the first year of the Mk 2, with dual seat.
    1957 Ariel Square Four Mark 4 Prototype 1957 Ariel Square Four Mark 4 Prototype
    1958 Ariel Square 4 Ariel Square 4
    1959 Ariel Square Four 1000cc 1959 Ariel Square Four Image supplied by

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