| MODEL | BSA B31 350 1945 - 1959 |
| Year | 1945 - 1959 |
| Engine Type | Four-stroke, single cylinder, OHV |
| Displacement / Capacity | 348 cc / 21.2 cu in |
| Bore X Stroke | 71 x 88 mm |
| Compression Ratio | 6.5:1 |
| Cooling System | Air cooled |
| Max Power | 16.2 kW / 22 hp @ 6000 rpm |
| Max Torque | — |
| Ignition | Lucas MO1L magneto |
| Induction | Single Amal type 76 |
| Start System | Kick start |
| TRANSMISSION SPECS | |
| Lubrication | Dry sump |
| Gear Box | 4-speed manual |
| Clutch | Multi-plate |
| Final Drive | Chain |
| CHASSIS SPECS | |
| Frame | — |
| Front Suspension | Hydraulic telescopic fork |
| Rear Suspension | Swinging arm with shock absorbers |
| Front Brakes | 8 in drum |
| Rear Brakes | 7 in drum |
| DIMENSION SPECS | |
| Overall Length | — |
| Overall Width | — |
| Overall Height | — |
| Seat Height | — |
| Wheelbase | — |
| Ground Clearance | — |
| Dry Weight | — |
| Wet Weight | 175 kg / 385 lb |
| WHEEL SPECS | |
| Front Tyre | 3.25 x 19 |
| Rear Tyre | 3.50 x 19 |
| FUEL SYSTEM | |
| Fuel Capacity | 19 Litres / 5 US gal |
| Fuel Consumption | — |
| Top Speed | 110 km/h / 70 mph |
BSA's workhorse 350 cc overhead-valve single and its first new post-war model, built on pre-war designs and the basis for the Gold Star. It began with a rigid frame and telescopic forks, gained plunger and then swinging-arm rear suspension, and ended in 1959 when the magdyno gave way to alternator and coil ignition.
