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1956 Ariel Square 4 1000cc

A sought-after machine in superb condition all round

Frame number: GM421
Engine number: ML405
First registered 17th March 1956
V5C registration document (age-related reg)
Recently MOT'd and taxed

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SQUARE FOUR MODELS: 1931-1958

From 1931 to 1958 Ariel produced 15,639 Square Four motorcycles.

Ariel ran into financial trouble in the late 1920's and closed shop for a short period while the founder's son, Jack Sangster, took over and restructured the company. With his life savings he bought all of the tools, re-hired the best of Ariel's staff, and then moved 500 yards down the road to a new factory. In 1928 Edward Turner proposed a very interesting new engine design, sketched on the back of a pack of Wild Woodbine cigarettes. He had shown it to the motorcycle factories to find a buyer for the innovative design, but only Sangster at Ariel was interested. He offered Turner space at the new Ariel factory as well as the services of a junior draftsman, Bert Hopwood. After 18 months of intense development (mid-1930) the Ariel Square Four was unveiled internally.

Four cylinder engines had been built in a variety of configurations for 25 years previously, and included the in-line four, the v-four, and the transverse four. Turner decided they were inefficient and too large. He proposed the Ariel Square Four, the only motorcycle to have four cylinders arranged vertically and equidistant to form a square. The front two cylinders drove one crankshaft, and the rear two drove another. A helically toothed flywheel gear was in between. When these gears meshed, the crankpins of one shaft were at top AND bottom dead centers while the crankpins of the other were at half- stroke. This resulted in perfect balance and no vibration at any speed, all in a very compact unit.

At its public unveiling at the Olympia Motorcycle Show in late-1930 the 1931 Ariel Square-Four caused a huge sensation, even over the new Matchless Silver Hawk narrow-angle v-four OHC. The first Square Four production models were 497cc lightweight touring bikes but the public wanted more power so Ariel increased the capacity to 597cc in 1932 models. Since the four air-cooled cylinders were set in a square formation (two 180º parallel twins placed back to back) and the OHV gear was operated by a chain-driven camshaft, the early Square Fours experienced inadequate cooling and, therefore, overheating.

But in 1931 Ariel won the much coveted Maudes Trophy, a test of durability, reliability, and ease of use. It also averaged 60mph for 700 miles! The famous Ariel 7 test involved seven different Ariel models attempting tests related to the number 7. The test for the Square Four involved seven schoolboys where each one kick-started the Square Four 7 times each. The Square Four started on 48 of 49 kicks.

In November 1935 the Square Four went through a complete redesign, which replaced the camshafts with pushrods and the crank and crankcase were completely changed, now producing 997cc. The new 4G reduced the 4F "cammy" tendency to overheat around the cylinder head.

To prove the new design & gain publicity, Edward Turner had Freddie Clarke ride a 1936 Square Four 1000cc to Brooklands track and ran "ten mph to a hundred in top". By 1937 the British rearmament program put people back to work and motorcycle sales skyrocketed and the Square Four became "monarch of the multi's".

In 1949 the Mk I 1000cc was introduced (above), and the engine became an all alloy type (reduced weight by 33 lbs) with the overall handling and acceleration improved. This style was built through 1953. The popular Mk II 1000cc was built from 1953 to 1958 and featured the 4-pipe exhaust system. Its revised cylinder & head layout featured separate cylinders vs. the Mk I monobloc casting to promote more efficient cooling.

Over its 27 years of production, the Square Four evolved through progressive advancements: a chain tensioner, swinging arm rockers versus pushrods, and a special ducting system to transfer cooling air to the rear cylinders. It was so well-known for its reliability that law enforcement agencies used it as their vehicle of choice.

text thanks to the Ariel Motorcycle Club of North America (http://www.arielnorthamerica.org/squarefour.htm)

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This beautiful Ariel Square Four is owned by my friend Stuart. I've seen it and heard it run and it is probably one of the nicest Square Fours I have come across.

It is sold in good running order.

http://www.BuyVintage.co.uk