Ariel Square Four
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Edward Turner conceived the Square Four engine in 1928. At this time he was looking for work, showing drawings of his engine design to motorcycle manufacturers. <ref name="mathews">[1] MathewsCollection 1955 Ariel (Retrieved 10 November 2006)</ref> The engine was essentially a pair of 'across frame' OHC parallel twins joined by their geared central flywheels, <ref name="bike">[2] MotorbikeSearchEngine 1932 Ariel (Retrieved 10 November 2006)</ref> with one fourcylinder block (or Monobloc) and one head. <ref name="real">[3] RealClassic Square Four (Retrieved 10 November 2006)</ref> The idea for the engine was rejected by BSA, but adopted by Ariel. Thus it became the Ariel Square Four.
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[edit] Ariel Square Four 4F (1931 - 1936)
The first Ariel Square Four 4F <ref name="north">[4] ArielNorthAmerica Ariel History (Retrieved 10 November 2006)</ref> was shown at the Olympia Motorcycle Show in 1930 in chain driven overhead-camshaft 500 cc form. <ref name="practical">[5] PracticalClassics Auction Lot 812286515 Ariel Square Four (Retrieved 10 November 2006)</ref> Early Square Fours used a hand-change, four-speed Burman gearbox. <ref name="real"/>
In 1932 the cylinder bores were enlarged by 5 mm to give a capacity of 601 cc. This model was used for the Maudes Trophy test, covering 700 miles in 700 minutes, followed by a timed lap of 87.4 mph. <ref name="bike"/> (In 1923 a Mr George Pettyt, of Maudes Motor Mart, had donated a "challenge trophy" for the ACU to award each year for the most meritorious, observed endurance test for motor cycles, known as the Maudes Trophy.)<ref>[6] KettleClub Maudes Trophy Run (Retrieved 10 November 2006)</ref>
[edit] Ariel Square Four 4G (1936 - 1949)
The “Cammy” engine gained a reputation for overheating the rear cylinder heads, so in 1936 the engine was completely redesigned, emerging as the 1937 OHV 995 cc model 4G. <ref name="mathews"/> In 1939 Ariel's patented Anstey-link plunger rear suspension became an option. <ref name="practical"/>
In 1946 the plunger rear was available again, and oil damped telescopic front forks replaced the previous girder type. <ref name="practical"/>
[edit] Ariel Square Four Mark I (1949 - 1953)
In 1949 the Ariel Square Four Mark I saw the cast-iron cylinder head and barrel replaced by alloy head and barrel. <ref name="practical"/> This saved about 30 lb in weight. The 1949 machine weighed around 435 lb dry, produced 35 bhp at 5500 rpm. <ref name="real"/> The Mark I was capable of 90 mph-plus.
[edit] Ariel Square Four Mark II (1953 - 1959)
In 1953, the ‘four pipe’ 997 cc Ariel Square Four Mk II was released, with a separate barrels and a re-designed cylinder head, with four separate exhaust pipes. <ref name="north"/> The Square Four was now a genuine 100 mph motorcycle. <ref name="practical"/>
In 1954 Ariel built prototypes of a Mk3 with Earles forks, but the model was never put into production. <ref name="real"/>
In 1959 Square Four production, and that of all other Ariel four-stroke models, ceased. <ref name="practical"/>
[edit] Figures
[edit] 1955 Square Four Specifications
- Make : Ariel
- Model : 4G MK II
- Year : 1955
- Engine : Square Four
- Capacity : 997 cc
- Power : 42 bhp
- Transmission : 4 speed
- Brakes : Drum
- ength : 82"
- Width : 32"
- Height : 44"
- Weight : 460 lb
<ref name="mathews"/>
[edit] Square Four Production
| Model | Years Produced | Production |
|---|---|---|
| 4F-500 | 1931-32 | 927 |
| 4F-600 | 1932-40 | 2674 |
| 4G-1000 | 1936-48 | 4288 |
| Mk I | 1949-53 | 3922 |
| Mk II | 1953-58 | 3828 |
| All Models | 1931-58 | 15,641 |
<ref name="north"/>
[edit] Ariel Square Four specifications (1958)
- Engine: Aircooled 8-valve OHV pushrod square four
- Capacity: 997 cc (65 x 75 mm)
- Power: 45 bhp @ 5500 rpm Weight: 211 kg(465 lb)
- Top speed: 105 mph (168 km/h) <ref>[7] Is-it-a-lemon Ariel Square Four (Retrieved 10 November 2006)</ref>
[edit] Pre-War Ariel Square Four Model Designations
- 1931-1932: 498 cc 4F/31 Square Four.
- 1932: 498 cc 4F Square Four.
- 1932-1936: 601 cc 4F/600 Square Four.
- 1937-1948: 995 cc 4G Square Four.
- 1939: 599 cc 4F/600 Square Four.
[edit] Sources
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