Description
Sunbeam 1922 “3½ h.p. T.T. Sporting Model“ 492cc side valve frame # 05594 engine # 169/17211
After the Great War, Sunbeam’s first new design was a side valve of 77mm bore and 105.5mm stroke, known at the works as the ‘Longstroke’ to differentiate it from its short-stroke predecessor. The new engine made a fantastic impression at the 1921 French Grand Prix on July, 24 at the Circuit de la Sarthe near Le Mans. The circuit length was about 17 km and the machines in the 250, 350 and 500cc classes, more than 40 in all, started at the same time. The 500cc class had 26 competitors who had to do 18 laps and from lap three Sunbeam riders Alec Bennett and Tommy de la Hay were firmly in the lead. Bennet won with an average speed of 59.9 mph (more than 95 km/h), 2 minutes in front of de la Haye. For the 1922 model year a sports machine based on this successful racer was available to the public. A quote from the description in The Motor Cycle’s issue of November 10th, 1921: “One’s first impression of the new T.T. model conjures up the simile of the thoroughbred racehorse, as compared with the more robust hunter, to which the 1920 sports model approximates. There is something of that “slimness” which suggests speed in the slightly lengthened frame. The saddle position is lower, and the handle-bar, instead of being fixed at the head of the steering post, is carried on two brackets extending rearwards and downwards from the head clip. Thus the handle-bar is actually lower than the top of the head tube, which is fitted with a cap. The shape of the bar is particularly graceful, and the average rider will find on assuming a natural riding position that his hands drop on to the grips. As before mentioned, the T.T. engine is a new design of the long-stroke type, the bore and stroke being 77mm and 105,5mm respectively (492c.c), and the compression ratio rather higher than is usually the case. The ports are designed to give an exceptionally big sweep, which brings both the induction and exhaust pipes lower down the cylinder than in the other models. An aluminium single-ring piston is adopted, and this, in conjunction with the other light reciprocating parts, gives the engine remarkable acceleration.“ The Longstroke, in its various guises, was in production for 17 years – the longest of any Sunbeam model.
This early specimen is basically a 1922 model as demonstrated by the engine and frame numbers, but it has been updated a bit to make it a more rideable and safer machine. The dummy-rim front and rear brakes have been replaced by Sunbeam’s internal expanding brakes, that became available a few years later. An external Best & Lloyd oil pump has been fitted for more reliable lubrication – Sunbeam started using these pumps in 1925 – and a kick-starter has been adopted to do away with push-starts. Magneto is ML, carburettor is Amac. The wheels are shod with 26 x 2½ Dunlops. This restored Longstroke comes with bulb horn and is an excellent runner.