BSA B31 / 33

BSA B31 / 33

BSA B31 / 33, BSA stands for Birmingham Small Arms. And what does a weapons factory do if peace breaks out? As a weapon manufacturer, they first started to produce bicycles and bicycle parts and only then - from 1907 to 1939 - cars. From 1910, also motorcycles. BSA was once very large and leading worldwide.

A BSA with the Shell

A gentleman of standing, a photo while refueling. AMK reader Jan Eggink is a pure-bred technician. He loves old motorbikes and cars and lives directly opposite a gas station. And Jan photographs. He gladly sent the header photo with this text. And such a BSA B31 or B33? That was a lot at the time!

The BSA B models

The B models were made from 1945 to 1960. They were still 'pre unit' blocks, where the engine block and the box were separate units that were connected by a - often leaking - primary box. The shock absorber in that system was one of the Flintstone 1.0 type. Two spring-loaded cam bushes had to absorb the blows.

The BSA B31 appeared in 1945 with a rigid frame and for a telescopic fork. In 1946 came the BSA B32, a sporty version of the 31. The BSA B33 was launched in 1947, and in the same year there was also a sporty BSA B34. Plunger rear suspension was supplied from 1948. The rear suspension received a swing arm in 1954. Two years later in 1956, the factory fitted full hubs in the front and rear wheels.


Another two years later, in 1958, the DC alternator was replaced by an alternator, which sat directly on the crankshaft. The BSA B31 disappeared in 1959 and the B33 in 1960. The BSA B 33 was the big 500 cc brother of the 350'er B31. First they came just after WWII as pure classics with a rigid rear frame and they were quite lively, sporty. With the swingarm and telescope they had become quite meatier. From that time on, you could compare them with the Mercedes 220 and 240 diesels. Good but reliable and not without status. Think smaller entrepreneurs (BSA B31) and veterinarians (B33).

Looks like a Gold Star enough ...

A little later in life they looked like the legendary Goldstars to be pimped en masse. Just for the beautiful, or purely as a 'wannabbee' bike. Or as a replica or falsification. In the sixties, the pre-unit blocks were also appreciated in motocross. There they died in bushes. Because everything can break. All in all, therefore, few standard B 33s remain.

Pure quality, high-quality materials

But when you see such a machine now, it is a matter of pure enjoyment from the days when aluminum was not yet so heavily alloyed with zinc that it already starts to show crumbly cauliflower growth when you cough over it wet. Such a BSA has now become an industrial monument. And the time when every fat British one-person sat with an owner who cherished him? The time when these machines were almost untraceable on the market? It's a bit over. There are quite a few owners whose kickstart knee is no longer kick resistant. Or worse. So the supply is growing slowly ...

More articles about classic engines through this link.

Also read:
- BSA A65. A nice machine, a bad start
- The BSA B33. Scraping or getting rid of?
- BSA, 'More for men'
- BSA, also such a piece of lost glory
- The Yamaha XS1. The best engine that BSA has never built

BSA B31 / 33
BSA B31 / 33


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  1. I had a friend in the late sixties who had also got such a kickstarter foot from his BSA B33 and who later found the solution, he made a slightly thicker head gasket from copper and he checked (he told) with a feeler gauge around the space between the top of the cylinder and the bottom of the cylinder head and ensured that the space around the space was exactly the same, and no more kicking back, I tried it out and indeed did a good kick at once and plow plow plow and no dreaded blow back.

  2. Too bad nothing was reported about the BSA trikes and the BSA scout .. a revolutionary sports car front wheel drive which was built until 1940 .. by order of UK government in war only engines. Want to know more? I have one and have a lot of info. Ms. Harry Scheper

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