Sunbeam 1932 Model 90 Road Racer 493 cc 1 cyl OHV 3607

Sunbeam 1932 Model 90 Road Racer 493 cc OHV frame # E13074 engine # NN6053 gearbox # BW1754F

The Model 90 first appeared in the firm’s catalogues for the 1927 season. Sunbeam had tried to develop an OHC racer but that proved to be unsuccessful: the camshaft Sunbeam that appeared in 1925 was seriously lacking in torque and power because of problems with valve timing. The much more direct ohc mechanism necessitated a totally different valve timing, of which there was very little knowledge at the time. Factories like Velocette and Norton decided to carry on experimenting and finally got the knack, but Sunbeam returned to the pushrods.
The factory turned to advice to Harry Weslake, who discovered the importance of the right shape of port and the optimum direction of gas flow. On this then new technology Harry Weslake built a career as an engine consultant- the splendid XK Jaguar engine was one result, the excellent reputation of the Model 90 another.
The engine was internally much different from the standard machines, with highly polished I-section conrod, 7.5 : 1 piston running in a special machined barrel. The head had enormous port finning and hairpin valve springs. The model 90 was very successful in racing for a number of years; in 1929 Charlie Dodson won the Isle of Man TT with an average speed of 73.5 mph. At Monza the Senior TT was won with a Model 90 that lapped the circuit at 94 mph. The last model 90 was made in 1933.
The machine we offer comes with an extensive history and information file. A set of photos, one of which was apparently taken in 1992, show the machine in as-found condition with reg nr JJ7747. A note records that this Model 90 was discovered when a long-established Northampton motorcycle dealer’s premises were being demolished. The machine had reportedly been hidden behind a false wall and was heavily coated in Castrol R, which had solidified and required extensive cleaning. The machine appeared to be composed of parts dating from around 1930-32. A letter from the Marston Sunbeam Register provides a detailed breakdown of the machine’s specification. The engine, carburettor and gearbox are described as 1932 Model 90, with the gearbox possibly being a Model 95 racing type featuring heel-and-toe change and no kickstart. The oil tank is described as a 1930 Model 90 (non-TT pattern), while the fuel tank is identified as a 1934-35 Model 95 type of enlarged capacity, as used to reduce pit stops. Other components are described as follows: front brake 1930 Sunbeam; front mudguards and stays Model 90 or 95; and rear mudguard likely Model 9. The correspondence also notes that many machines were progressively modified from Model 90 to Model 95 specification during the early 1930s, both by private owners and by the works, where such machines were used as practice and ‘hack’ machines for Manx riders before being sold on.
Sunbeam authority Robert Cordon Champ stated in a letter that in his opinion, the machine represents a fast road special constructed circa 1933.
Originally the machine ‘s frame was of 1930 pattern (no. E7430). The former owner, who acquired the M90 in May 1988, had a large collection of Sunbeam motorcycles and spares, and we think he restored and rebuilt the Model 90 around a genuine 1932 frame, to make the machine more period-correct.