General data
Engine: Single port, 496cc OHV single cylinder.
Bore 82mm, Stroke 94mm.
Compression ratio 7.75:1
(Option of 12.5:1 with High Compression Piston)
Power output 29-30bhp @ 5,800rpm
Alloy cylinder head with cast-in bronze thread inserts, and
screwed-in steel valve seats.
Alloy cylinder barrel with pressed-in steel liner
Valves: Inlet: length 4.21875in Head Dia 1.65625in Stem Dia 0.34375in
Exh: length 4.21875in Head Dia 1.59375in Stem Dia 0.375in
Ignition: Lucas MO1 Magdyno with manual advance.
Carburettor: 1938: Amal 10TT36 1 & 5/32” bore, Main Jet 370,
Throttle valve 5, needle groove 4 1939: Amal 10TT38 1 & 5/32” bore, Main Jet 350,
Throttlevalve 6, needle groove 4
Transmission:
Gearbox: 4-speed, enclosed footchange, external clutch release lever
Magnesium Alloy (Elektron) gearbox cases for 1938 only
Close-ratio gears for 1939, with option of standard wider ratios Ratios: 1938 & 1939 standard:
1st 14.3:1 2nd 9.9:1 3rd 6.3:1 4th 4.8:1
1939 Close ratio:
1st 11.85:1 2nd 8.3:1 3rd 5.25:1 4th 4.8:1
Clutch: 6-spring multiplate with 43 tooth chain wheel,
driven by ½ x .305in single row primary chain from 21 tooth
cush-drive engine sprocket. 18 tooth gearbox sprocket,
driving 42 tooth rear wheel sprocket via 5/8 x 1/4in. final drive chain.
Frame: Reynold 531 high-tensile tube. Single front down tube, rigid rear,
BSA girder front forks.
Wheels: 20in WM1front, (21in WM1 on Competition Model), 19in WM2 rear.
Tyres Front 3.00 x 20in, Rear 3.25 x 19 (1938), 3.50 x 19 (1939)
Brakes: 7in Single LS drum brakes front & rear.
Petrol Tank Capacity: 3 Gal. (1938) 3.5 Gal. (1939)
Oil Tank Capacity: 4 pints (1938) 5 pints (1939)
Wheelbase: 54in
Saddle Height: 28.5in
Ground clearance: 4 .625in
Dry weight: 345lb 1938 & 1939
