Description
National Motorcycle Museum | Solihull, West Midlands
26th March 2025 - 9:00AM
1955 Ariel Square Four Mk2
1000cc '4-pipe' model
Estimate
£5, 000 - £7, 000
Registration No: 921 DTW
Frame No: GM660
MOT: Exempt
Authentically restored Mk2 1000cc model
Unique Square Four engine configuration
Supplied with receipts, green logbook and a V5C
Like many British motorcycle companies, Ariel began producing bicycles in the late 1800s eventually progressing onto motorcycles in 1902. After a typically rocky few years for manufacturers in the early part of the century, the company was bought by Jack Sangster from the receivers at a bargain price in the early 1930s. The company was renamed Ariel Motors (J. S.) Ltd, and promptly resumed production in a new factory in Selly Oak Birmingham. One of their first bikes produced was the Ariel Square Four designed by Edward Turner, who at the time was looking for work and showing drawings of his engine designs to various motorcycle manufacturers. The design was rejected by BSA but adopted by Ariel, becoming their prestige model for the next 30 years. In the days of predominately single-cylinder engines a square four layout was very advanced and the bike stayed in production until the late 1950s. The engine was initially a 500cc with overhead cams and was essentially a pair of across-frame parallel twins joined by their geared central flywheels before being bored out to 600cc in 1932. A very expensive engine to produce, it was given a major revamp in 1939 to become an easier to manufacture 1000cc motor with overhead valves in place of the OHC.
This authentically presented Square Four is the later Mk2 model with four separate exhaust pipes exiting from two aluminium manifolds and a rocker box combined with the inlet manifold. Part of an enthusiast's small private collection, it has been restored keeping a good degree of originality, starting and running whilst being photographed (see video). Noted for their smooth running and torquey power delivery, Square Fours still make good classic bikes for use on Vintage runs and rallies with enough power to keep up with modern day traffic. A unique chapter in British motorcycle history, it comes supplied with a few receipts, its original green logbook and a current V5C.
