Make Model



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


(71-72) Amal R932/18, (73) Amal R932/28

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

3.5 x 18 in.


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

178 mm / 7 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

145 km/h / 90 mph


Introduced in 1971, the B50MX (Motocross) was the last competition motorcycle announced by BSA, just as the company’s efforts came to a close. Developed through the great success of the BSA ‘works’ machines in motocross, and using bikes based on the B44 Victor, the B50MX offered a strong and powerful 500cc engine. A new chassis design which saw the introduction of an oilbearing frame and its extreme slimline aesthetic that was enhanced by a beautiful tucked-in exhaust system ensured this machine’s place in history as it was one of the rarest and most successful BSA MX designs of the period.


The BSA B50 MX was the final competition motorcycle ever built by BSA, a proud British motorcycle manufacturer who had built a staggering number of race winning motorcycles over its decades long history.

As the name suggests, the B50 MX was the motocross version of the standard B50. It was designed exclusively for off road competition with as much weight saving as possible, the final production motorcycle tipped the scales at approximately 300 lbs or 136 kgs.

The B50 is powered by a single-cylinder, four-stroke, air-cooled 499cc OHV unit-construction engine producing 34 hp and sending power to the rear wheel via a 4-speed transmission. The model uses a tubular steel duplex cradle frame with oil stored in the top tube, and it has standard drum brakes front and back.

BSA produced the B50 in three distinct model variations, the BSA B50SS (Street Scrambler), the BSA B50T (Trail), and the BSA B50MX (Motocross). Production lasted from 1971 until 1973, after which time BSA ceased to function but a small number of B50s were still sold rebadged as the Triumph TR5T Trophy.

Despite the relatively low production numbers the B50 did still enjoy some successes on the race track thanks to specially modified bikes built by Mead & Tomkinson in England. These bikes would win the Zolder 24 Hour race outright and take class wins in the 1971 Thruxton 500 Miler and the Barcelona 24 Hours, they also set a class lap record in the Production Isle of Man TT.

By the time BSA released the B50 series of motorcycles in 1971 the British had enjoyed decades of dominance as one of the world’s leading motorcycle producers, and one of the most successful builders of four-stroke, off-road racing motorcycles.

It would be the late 1960s and early 1970s that would see this period of success come to an end for the Brits, two stroke motorcycles from the likes of Husqvarna and other European manufacturers had been chipping away at their lead but it would be the arrival of fast, inexpensive motorcycles from Japan that would mark the end of the British motorcycle industry.

Sadly for the B50 it wasn’t able to compete with the inexpensive, lightweight, and very quick two-stroke motorcycles that had come to dominate off-road motorcycle racing. The downfall of BSA and many other marques was directly attributable to poor company management and product planning, whereas the actual motorcycles themselves were often great.

The BSA B50 has now become a popular lightweight vintage scrambler with plenty of torque and a much lighter, more manageable construction that makes it easier to ride off road than other British off roaders of the era like the Triumph TR6 and the Norton P11.

Source silodrome.com