Ariel - SG 31 Sloper
 Back to brands list

Ariel D2-492-85-12
Photo ou archives : M. Woollett

Capacity : 500
Model : SG 31 Sloper
Production : 1931 -
Category : (R) Street Bike


500 SG31 – 1931

Four-valve sportster

They say that history repeats itself. That's certainly true as far as the technology of four valves per cylinder, so proudly proclaimed by auto makers in the 1990s, is concerned, since this configuration was commonplace on sports bikes 60 years ago!

Racing Success

Rudge of Coventry pioneered this trend, and the competition success enjoyed by its machines - notably the double victory of the 350 Junior and 500 Senior Isle of Man TTs in 1930 - did a great deal to popularize the four-valve head among enthusiasts.

Superb Single

Several British marques jumped on the four-valve bandwagon, including the proud old Ariel company. Its renowned chief engineer, Val Page, designed a 500cc single with its cylinder horizontally inclined at 30 degrees. It’s valves were actuated by pushrods and rockers, and - in keeping with the fashion of the day - it had twin exhaust downpipes terminating in fishtail mufflers. While Val Page worked on the SG31, his assistant, Edward Turner, was designing his Ariel Square Four, which was also launched in 1931. The first Square Four (named for the layout of the cylinders) designed by Turner was an overhead-cam 500. To minimize production costs, the same double-loop frame was used for both models. Very few SG31s were built - because of the slump, Ariel slashed its budgets and the model was abandoned. However, Turner's Square Four remained in production and was progressively uprated, first to 600, then to 1000cc.


Engine: 498cc (86.4x85mm) air-cooled single-cylinder four-stroke inclined at 30 degrees; magneto-ignition

Power Rating: 15 hp @ 5500 rpm

Valves: overhead; 4 valves

Fuel System: Amal carburettor

Transmission: 3-speed, chain primary and final drives

Suspension: girder forks (front); rigid (rear)

Brakes: drum (front & rear)

Wheels: 19 inch (front & rear)

Weight: 355 lb

Maximum Speed: 70 mph

With its four-valve head, steeply inclined cylinder, dual fishtail exhausts and instrument panel on the rear of the chromed tank, the Ariel SG31 was every inch a sports 500.

Motorcycle encyclopedia Moto Passion, realised by François-Marie Dumas, include almost 2000 photos presented with an exhaustive history of the motorcycles exhibited.

This unique collection has been realised with the participation of many specialists. With many thanks in particular to Yves Campion, Michael Dregni, Didier Ganneau, Jean Goyard, Helmut Krackowizer, Michel Montange, Christian Rey, Bernard Salvat, Mick Woollett, etc

One can order here

  • Original cards on paper (in french)
  • High resolution scans or original documents presented and signed with my name.

Please contact me at for conditions and copyright.

© Tous droits réservés
François-Marie Dumas

Accueil - Motos NOUGIER - Motos insolites - Motos japonaises - Unusual Motorcycles - Scooters du Monde - Motos Passion - Motos GILLET - Liens - Contact

Moto Collection - François-Marie Dumas

Valid XHTML 1.0 Transitional CSS Valide !

Mentions légales