Home ENGINEERING Triumph Model SD 1920 550cc One Cylinder

Triumph Model SD 1920 550cc One Cylinder


This older restoration SD in the 550cc class with its 3 speed gearbox runs very well and smooth. Its full equipped with a Triumph carburetor, Acethelene lighting set, Smiths speedo, hand operated horn and a front brake to makes it more road suitable.

source.image: classic-motorcycle.com

The first Triumph motorcycle of 1902 used a Belgian Minerva engine but within a few years the Coventry firm – originally a bicycle manufacturer founded by German immigrants Siegfried Bettman and Maurice Schulte – was building its own power units. The company was soon involved in racing and the publicity generated by competition success – Jack Marshall won the 1908 Isle of Man TT’s single-cylinder class for Triumph having finished second the previous year – greatly stimulated sales.

By the outbreak of The Great War the marque’s reputation for quality and reliability was well established, leading to substantial orders for ‘Trusty Triumphs’ for military use. Triumph’s 3½hp model had first appeared in 1907. Originally of 453cc, its sidevalve engine was enlarged to 476cc in 1908 and finally to 499cc in 1910 before being superseded by the 550cc 4hp model in 1914.


Equipped with three-speed Sturmey-Archer gearbox, it was this revised 4hp – the Model H – that did such sterling service in WWI, some 30,000 ‘Trusty Triumphs’ seeing action with British and Allied forces. Updated with chain final drive for 1920, it became known as the ‘SD’ (Spring Drive) because of its clutch-mounted, coil-spring shock absorber and formed the basis of the later four-valve Ricardo model.