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BSA B50T

"B50SS"

Make Model	BSA B50T
Year	1971 - 73
Production	5700 units
Engine	Four stroke, single cylinder, OHV, 2 valve
Capacity	499 cc / 30.5 cub in.
Bore x Stroke	84 x 90 mm
Carburettors	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
Ignition	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
Transmission	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	3.00 x 20 in. Trials
Rear Tyre	4.00 x 19 in. Trials
Dimensions	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	191 mm / 7.5 in.
Seat Height	813 mm / 32 in.
Dry Weight	135.0 kg / 298 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

Of the 5,700 or so that were built, survival rates are low. Which is partly why today the B50 is as rare as a priest with a clean conscience. It’s not the easiest bike to live with. And it needs a good dose of retro-engineering to get the very best from it. But you can be sure that ownership of one will, at least, never be dull.

But was it ever worth the hallowed Gold Star name that was bestowed upon it? It’s a debate that still rages.

Overall, these are great little BSA singles. You wouldn’t want to ride two-up on one—unless most of your journeys were shorter rather than longer. But as a solo mount, it’s a stylish thumper with a hidden chunk of lead in its glove.

Remember to duck.

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.