We are proud to offer this 1954 Ariel Square Four MK II, Engine Number: PL269. This bike has been restored to original manufacturer specifications with no modifications. The 12,000 miles are original, and this excellent condition Square Four is completely functional.

The Square Four was produced between 1931 and 1959, designed by Edward Turner, who devised the Square Four engine in 1928. At this time he was looking for work, showing drawings of his engine design to motorcycle manufacturers. The early engine with “two transverse crankshafts” was essentially a pair of ‘across frame’ OHC parallel twins joined by their geared central flywheels, with a four-cylinder block (or Monobloc) and single head. The idea for the engine was rejected by BSA, but adopted by Ariel. Thus it became the Ariel Square Four.

In 1953, the ‘four pipe’ 997 cc Ariel Square Four Mk II was released, with separate barrels, a re-designed cylinder head with four separate exhaust pipes from two cast-aluminium manifolds and a rocker-box combined with the inlet manifold. A redesigned frame provided clearance for the high-mounted, tall, car-type, SU carburettor. This 40 hp (30 kW) Square Four was capable of 100 mph (160 km/h). It weighed425 lb (193 kg) and cost £336.16.

This particular Square Four has been part of a private collection collection for a several years. It was restored by Chuck Walton. Chuck has re-built over seventy-five Square Four engines and is considered to be one of the foremost experts on this model. The tank, side covers, and rear fender were recently restored to period correct trim and colors and look beautiful. The brakes work great and it shifts exactly the way it should.

Chuck also rebuilt the engine and transmission, and installed all the upgrades available. Besides new pistons, valves, and lower and bearings, the engine has a Morgo oil pump, Mark I rods, German head gasket, and the cylinder barrels have had Timeserts installed in the threaded holes to help prevent future head gasket problems. The transmission and primary case have also been machined by Homer Knapp to accept modern seals and prevent leakage.

The magneto and charging system are all OEM and working correctly. Also, it is very common on the Square Four for the crank oil passages to become plugged up. Square Fours will throw a connecting rod due to the cranks getting plugged up if this is not addressed! The oil passages and sludge traps on this bike were fully cleaned, and as stated before, a new high volume Morgo oil pump was installed, as well as an aftermarket oil filter kit to eliminate this issue.

The condition is exactly what it looks like in the photos and needs absolutely nothing to ride, show, and enjoy. This bike has a clear title.

For more information, contact Daniel at +1.917.890.4230 or at daniel@classicpromenade.com