Top fours: 4. Ariel Square Four-News & Reviews-Motorcycle Trader

25 Apr 2015 | Author: | Comments Off on Top fours: 4. Ariel Square Four-News & Reviews-Motorcycle Trader
Kawasaki Square Four 2 Stroke Prototype

20 Feb 2013 | Ian Falloon nominates the greratest of all time

Before World War II, in-line fours with the engine lengthwise were considered unwieldy, and across-the-frame fours too wide. Then one day in late 1928, a London motorcycle dealer, Edward Turner, sketched on the back of a cigarette packet the idea of two parallel-twins, two by two. Turner made a trip to the Midlands trying to sell the idea and it was Ariel that provided Turner with the resources to see his idea to fruition.

The first square-four (popularly called the ‘Squariel’) appeared in 1931 and was a single overhead camshaft 500. The basic layout of cylinders at the corners of a square with two 180-degree crankshafts geared together and contra-rotating, set the pattern for the future.

To make the engine more suitable for sidecar use, a 600cc version was added in 1932 but, as there were so many problems with the initial design, the engine was completely updated for 1936.

Although the new engine retained the two-by-two cylinder format, in most other respects it was totally revised. The valves were now pushrod operated, the capacity increased to 1000cc and the weight was reduced. The square-four continued until the outbreak of war largely unchanged and was resurrected after hostilities ended.

The post-war square-four initially retained the 997cc engine of the pre-war Squariel, but the addition of telescopic front forks and plunger rear springing saw the first post-war models weighing over 225kg. Ariel figured it was time to shed some weight and, for the 1949 MkI, the old cast-iron cylinder block and head were scrapped and substituted with alloy castings. The claimed weight saving was an optimistic 25kg but the real weight saving was 15kg.

The alloy castings also improved cooling and with a 6:1 compression ratio (to cope with the 72-octane ‘pool’ petrol) the engine produced 25.4kW (34.5hp) at 5400rpm.

With production spanning 27 years, Ariel’s square-four was never a mainstream motorcycle. Revered for its smoothness, comfort and acceleration, the Squariel was always expensive and appealed as a status symbol rather than regular transportation.

Ultimately a lack of development resulted in its demise but now the square-four is acknowledged as one of Britain’s finest classic motorcycles.

Early square-fours didn’t take to tuning and although Ben Bickell managed to lap Brooklands at over 175km/h, his supercharged 500 kept blowing cylinder-head gaskets and he never finished a race.

The four-pipe Mark II Square Four appeared in 1954, lasting until 1958. All Square Fours had plunger rear springing although two prototype pivoted-fork models were constructed but not put into production.

Ariel Square Four engines were produced under licence in Canada and used in pairs to power helicopters.


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