Sunbeam motor cycles 1931

1931
SUNBEAMS

Model Range
The model range from 1930 was severely pared down for 1931. Sunbeam was attempting to weather the Great Depression in the world's economy. The catalogue emphasised 'Sunbeam value' with lower cost machines (the Lion and new Model 10) replacing longstanding designs. It even provided details of a Sunbeam hire purchase agreement through the factory or recognised dealers.

Other than the 596cc 'Model 7' flat-tank machine (unaltered since 1928 and still available to order) the side-valve range was reduced to one machine: the cut-price 'Lion' introduced mid-season the previous year. Gone were the longstanding Marston side-valves: the 347cc 'Model 1' and 'Model 2' plus the 'Model 5' and 'Model 6' versions of the 492cc Longstroke.

The 347cc OHV 'Model 8' was also lost. However, it was replaced by a new introduction to the range; a John Greenwood and George Stephenson designed 344cc OHV machine named the 'Model 10'. This machine had a distinctive crankcase, holding a wet sump - a design only previously seen in the 1925 OHC racing machines. Its design did not allow for the use of Sunbeam's trademark enclosed rear chaincase. Roy Bacon also refers to Sunbeam offering a tuned version of the 'Model 10' for the mid-season in July 1931.

Mid-season, in July 1931, a 599cc version of the side-valve Lion was also added to the range. Designated the 'Model 7A', it introduced a side-valve engine with a detachable head and 'boxed-in' valve springs which became the standard side-valve design for 1932 and thereafter.

The 493cc OHV Model 9 in its standard and 'Model 90' sporting varieties continued to be available but it was now provided with the chrome tank and Webb-style forks of the newer models. 'Model 9' was available with both single and twin-port cylinder options; 'Model 90' only as a twin-port. The 'Model 90' was offered in both road racing and 'fast touring' trim.

Cycle parts
Druid forks are replaced by centrally sprung Webb-style front forks, made at Sunbeamland.

Chrome-plated, welded tanks were introduced - the petrol tank finished in chrome plate with black panels. Needless to say, it did not go down well and an all-black colour scheme returned in 1932.

Engine and gearbox
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Sources:
* John Marston Ltd, 1931, 'Sunbeam Motor Cycles 1931'.
* Robert Cordon Champ, 1980, 'The Sunbeam Motorcycle'. Haynes Publishing.
*Robert Cordon Champ, 1989, 'The Illustrated History of Sunbeam Bicycles and Motorcycles'. Haynes Publishing.
* Roy Bacon, 1986, 'British Motorcycles of the 30s'. Osprey Publishing

1931 catalogue cover

T H E Y E A R ' S M O D E L S
Model 10	Engine Cylinder capacity: 344cc Bore x stroke: 74mm x 80mm Compression ratio: 6 to 1 Gearbox Three-speed - medium ratio Gear ratios: 5.5, 9.1 and 15.2 (options: 5.15, 8.6 and 14.3 or 5.8, 9.7 and 16.5) Tyres Dunlop 25in x 3.00in (wired on) Pressure: front 17 lb; rear 23 lb Cycle Weight: 231 lb Overall length: 79in Wheelbase: 50.5in Width across handlebars: 32in Saddle: Terry (Lycett optional) Saddle height: 28in (minimum) Petrol capacity: 2 gallons Oil capacity: 2 pints Frame numbers: R1001 up Engine numbers: SS1001 up
Lion 'Longstroke'	Engine Cylinder capacity: 492cc Bore x stroke: 77mm x 105.5mm Compression ratio: 5 to 1 Gearbox Three-speed - wide ratio (AT prefix) Gear ratios: 4.9, 8.2 and 13.7 (side car: 5.25, 8.7 and 14.6 or 5.6, 9.3 and 15.5) Tyres Dunlop 26in x 3.25in (wired on) - 3.50in optional Pressure: front 16 lb; rear 19 lb Cycle Weight: 300 lb Overall length: 82in Wheelbase: 53.5in Width across handlebars: 32in Saddle: Lycett (Terry optional) Saddle height: 28in (minimum) Petrol capacity: 2.5 gallons Oil capacity: 4 pints Frame numbers: B9001 up Engine numbers: J5001 up
Model 9	Engine Cylinder capacity: 493cc Bore x stroke: 80mm x 98mm Compression ratio: 6.5 to 1 Gearbox Three-speed - medium ratio (BT prefix) Gear ratios: 4.6, 6.9 and 10.3 (optional: 4.3, 6.5 and 9.7 or 4.9, 7.4 and 11.0) (side car: 5.25, 7.9 and 11.8 or 5.6, 8.4 and 12.6) Tyres Dunlop 26in x 3.25in (wired on) - 3.50in optional Pressure: front 16 lb; rear 19 lb Cycle Weight: single-port 308 lb; twin-port 319 lb Overall length: 82in Wheelbase: 53.5in Width across handlebars: 32in Saddle: Terry (Lycett optional) Saddle height: 28in (minimum) Petrol capacity: 2.5 gallons Oil capacity: 4 pints Frame numbers: D9001 up Engine numbers: L5001 up (LL for twin-port)
Model 90	Engine Cylinder capacity: 493cc Bore x stroke: 80mm x 98mm Compression ratio: 7 to 1 (optional 7.5 or 9 to 1) Gearbox Three-speed - medium ratio (BT) or close ratio (CT) Gear ratios BT 'box: 4.6, 6.9 and 10.3 (optional: 4.3, 6.5 and 9.7 or 4.9, 7.4 and 11.0) (side car: 5.25, 7.9 and 11.8 or 5.6, 8.4 and 12.6) Gear ratios CT 'box: 4.6, 6.2 and 8.4 (optional: 4.3, 5.8 and 7.9 or 4.9, 6.6 and 9.0) (side car: 5.25, 7.1 and 9.6 or 5.6, 7.6 and 10.2) Racing option: foot gear change / no kickstarter Tyres Front: Dunlop 26in x 3.25 (wired on) Front - racing option: 27in x 2.75in (wired on) Rear: Dunlop 26in x 3.25 (wired on) Pressure: front 16 lb (27in tyre - 23 lb); rear 19 lb Cycle Weight: racing 312 lb; 'fast touring' 315 lb Overall length: 82in Wheelbase: 53.5in Width across handlebars: 35in Saddle: Terry (Lycett optional) Saddle height: 28in (minimum) Petrol capacity: 2.5 gallons Oil capacity: 5 pints Frame numbers: E9000 up Engine numbers: NN5001 up
Model 7 (flat-tank) - see flat-tank machines
Model 7A Note: introduced mid-season (July 1931) the earliest Model 7A inserts the new detachable-head engine design into the cycle parts of the 1930-31 Lion, including its three-speed gearbox. The new engine design was to become standard for both 500cc and 600cc side-valves from 1932 whilst cycle parts and gearbox were both subject to change.	Engine Cylinder capacity: 598cc Bore x stroke: 85mm x 105.5mm Compression ratio: 5 to 1 Gearbox Three-speed - wide ratio (AT prefix) Gear ratios: 4.9, 8.2 and 13.7 (side car: 5.25, 8.7 and 14.6 or 5.6, 9.3 and 15.5) Tyres Dunlop 26in x 3.25in (wired on) - 3.50in optional Cycle Weight: ? Overall length: 82in Wheelbase: 53.5in Width across handlebars: 32in Saddle: Lycett (Terry optional) Saddle height: 28in (minimum) Petrol capacity: 2.5 gallons Oil capacity: 4 pints Frame numbers: ? Engine numbers: ?
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