| MODEL | BSA 5.57 HP SIDE-VALVE 557 1928 |
| Year | 1928 |
| Engine Type | Single-cylinder four-stroke side-valve |
| Displacement / Capacity | 557 cc |
| Bore X Stroke | 85 mm x 98 mm |
| Compression Ratio | — |
| Cooling System | — |
| Max Power | — |
| Max Torque | — |
| Ignition | Chain-driven magneto |
| Induction | Amac carburettor |
| Start System | — |
| TRANSMISSION SPECS | |
| Lubrication | Gravity feed to a mechanical pump with sight feed to the crankcase, hand pump for emergencies |
| Gear Box | BSA three-speed, constant mesh, widened for strength, enclosed kick-starter |
| Clutch | Floating dry-plate, left-hand lever |
| Final Drive | Chain: front 1/2 x 0.305 in, rear 5/8 x 3/8 in |
| CHASSIS SPECS | |
| Frame | Weldless steel tube with forged lugs, sidecar lugs, steering damper |
| Front Suspension | BSA spring fork with barrel spring and shock absorbers |
| Rear Suspension | — |
| Front Brakes | Internal expanding, 7 in, right-hand lever |
| Rear Brakes | Internal expanding, 7 in, heel pedal |
| DIMENSION SPECS | |
| Overall Length | — |
| Overall Width | — |
| Overall Height | — |
| Seat Height | — |
| Wheelbase | — |
| Ground Clearance | — |
| Dry Weight | — |
| Wet Weight | — |
| WHEEL SPECS | |
| Front Tyre | 26 x 3.25 in Dunlop cord wired-on |
| Rear Tyre | 26 x 3.25 in Dunlop cord wired-on |
| FUEL SYSTEM | |
| Fuel Capacity | 1 7/8 Imperial gal (oil 3 pints) |
| Fuel Consumption | — |
| Top Speed | — |
The 557 cc side-valve was the big touring single, known for strong pulling power, economy and simplicity. It was built with sidecar work in mind, with sidecar lugs and a steering damper on the frame.
