BSA B50SS Goldatar

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.