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.[1] The engine was essentially a pair of 'across frame' OHC parallel twins joined by their geared central flywheels,[2] with one four cylinder block (or Monobloc) and one head.[3] 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[4] was shown at the Olympia Motorcycle Show in 1930 in chain driven overhead-camshaft 500 cc form.[5] Early Square Fours used a hand-change, four-speed Burman gearbox.[3]
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.[2] (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.)[6]
[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.[1] In 1939 Ariel's patented Anstey-link plunger rear suspension became an option.[5]
In 1946 the plunger rear was available again, and oil damped telescopic front forks replaced the previous girder type.[5]
[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.[5] This saved about 30 lb in weight. The 1949 machine weighed around 435 lb dry, produced 35 bhp at 5500 rpm.[3] 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.[4] The Square Four was now a genuine 100 mph motorcycle.[5]
In 1954 Ariel built prototypes of a Mk3 with Earles forks, but the model was never put into production.[3]
In 1959 Square Four production, and that of all other Ariel four-stroke models, ceased.[5]
[edit] Figures
[edit] 1958 4G Mk II Square Four Specifications
| Engine | 997 cc, 4-stroke, square four, air-cooled, OHV, 8-valve | ||
|---|---|---|---|
| Bore/Stroke | 65.0 mm x 75.0 mm | ||
| Compression Ratio | 7.2:1 | ||
| Max Power | 45 bhp @ 5500 rpm | ||
| Max Torque | |||
| Fuel System | Single SU carburettor | ||
| Lubrication | Double gear pump | ||
| Ignition | 6V 20A/h battery, coil ignition | ||
| Transmission | 4-speed | ||
| Final Drive | Chain | ||
| Overall Length | 82 inch | ||
| Overall Width | 32 inch | ||
| Seat Height | 30 inches (787 mm) | ||
| Wheelbase | 56 inches (1422 mm) | ||
| Dry Weight | 425 lb / (197 kg) | ||
| Suspension Front | Telescopic Forks | ||
| Suspension Rear | Twin link-and-plunger units | ||
| Brakes Front | 8-inch (203 mm) sls drum | ||
| Brakes Rear | 8-inch (203 mm) sls drum | ||
| Tires Front | 3.25 x 19 inches | ||
| Tires Rear | 4.00 x 18 inches | ||
| Fuel Tank Capacity | 5 imp gallons (23 litres) | ||
[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 |
[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
- ^ a b c [1] MathewsCollection 1955 Ariel (Retrieved 10 November 2006)
- ^ a b [2] MotorbikeSearchEngine 1932 Ariel (Retrieved 10 November 2006)
- ^ a b c d [3] RealClassic Square Four (Retrieved 10 November 2006)
- ^ a b c [4] ArielNorthAmerica Ariel History (Retrieved 10 November 2006)
- ^ a b c d e f [5] PracticalClassics Auction Lot 812286515 Ariel Square Four (Retrieved 10 November 2006)
- ^ [6] KettleClub Maudes Trophy Run (Retrieved 10 November 2006)
- ^ [7] Is-it-a-lemon Ariel Square Four (Retrieved 10 November 2006)
