BSA B50SS Goldatar


Make Model

BSA B50SS Goldstar


1971 - 73
Production 5700 units


Four stroke, single cylinder, OHV, 2 valve


499 cc / 30.5 cub in.
Bore x Stroke 84 x 90 mm


B50 SS & T Amal R930/62

Cooling System Air cooled
Compression Ratio 10.0:1
Lubrication Wet sump
Engine Oil SAE 20W/50
Oil Capacity 3.4 L / 6 pints / 0.9 US gal
Exhaust Single, chrome plated


Lucas RM21
Spark Plug Champion N4
Battery 12V
Starting Kick

Max Power

25 kW / 34 hp @ 6200 rpm

Max Torque

37.9 Nm / 3.86 kgf-m / 28 ft/lb @ 5000 rpm
Clutch Multi-plate, wet, cable operated


4 Speed
Final Drive Chain
Frame Welded frame with larger diameter top tube for strength

Front Suspension

Telescopic forks

Rear Suspension

Swing arm, 2 shocks wiith dampers

Front Brakes

8 in. drum, leading shoewith snail cam shoe adjustment

Rear Brakes

7 in. drum with floating cams
Wheels Steel, spokes

Front Tyre

 3.25 x 18 in.

Rear Tyre

SS & MX: 3.5 x 18 in.

T: 4.00 x 19 in. Trials


Length: 2159 mm / 85.0 in.
Width: 737 mm / 29.0 in.
Height: 1105 mm / 43.5 in
Wheelbase 1372 mm / 54 in.

Ground Clearance

SS & MX: 178 mm / 7 in.

T: 191 mm / 7.5 in.

Seat Height 813 mm / 32 in.

Dry Weight

140.6 kg / 310 lbs

Wet Weight 184 kg / 406 lbs

Fuel Capacity 

UK: 18.2 L / 4.8 US gal

US:   9.1 L / 2.4 US gal

Standing 0 - 100 km/h / 62 mph 7.4 sec (B50SS model)

Top Speed

160 km/h / 99 mph


The "SS" stands for "Street Scrambler", and was intended as the full street version of the 500cc single-cylinder B50 line. BSA dipped into its parts bin, borrowing from the 1971-and-later BSA A65 for the front forks, triple clamps, brakes and lighting. All of this was added to the B50's sturdy frame, which utilized a large-diameter backbone for both strength and to hold the engine oil, in lieu of a separate oil tank. A very shapely 2.4-gallon tank with a top-notch paint job topped of what was a very handsome machine. Some other things were done right too, like all the electrics being contained in one removable pod. The B50 in factory-racing form and bearing the hallowed name of "Gold Star", earned some racing cred in the early 70s by winning the Thruxton 500, the Barcelona 24-hour, the Zolder 24-hour, and set a class lap record at the Isle of Man TT.

BSA B50 tips

1. The unit single crankcases were originally designed for a 250cc engine. Accordingly, the B50 pressures beneath the piston are considerable and put a huge load on gaskets and seals. A timed breather is vital to keep the crankcase at negative, or at least neutral, pressure. Well-fitting mating surfaces are essential if you want to keep the oil in rather than out.

2. Poor handling is often attributed to the swinging arm bearings. These pivot on needle rollers and need plenty of grease to avoid seizure. Raise the bike and check for play. Replacement is straightforward.

3. The extra torque of the B50 means that clutches are prone to slippage and so need need to be kept in tip-top shape. Solutions include an extra friction plate, an extra steel plate, stronger clutch springs, and an alloy pressure plate.

4. The bore can be opened up to 90mm giving 572cc for extra stomp. You’ll also need to gas flow and fit a larger (32mm) carb.

5. Ignition coils were always weak leading to poor starting, irregular tickover, and misfires. Fit the best quality replacements you can afford along with a new condenser and quality plug lead.

6. Whilst good enough for general use, high performance B50s will require an upgraded crankpin such as Alpha. A Carillo conrod is also highly recommended.

7. Rocker boxes are prone to leakage which can be sorted by careful linishing.

8. Poor crankcase scavenging seems to affect some bikes more than others, and is said to be due sometimes to mismatched sump covers blocking oil pick-up holes.