1957 BSA B31

Description

UNSOLD AT AUCTION February 2024
Please contact Evoke for more information / to arrange a viewing : team@evoke-classics.com
350cc
Matching numbers
Dual seat

We live in a world where anything from a mobile phone to a motorbike comes with mind numbing complexity. Birmingham Small Arms Company ie BSA, knew how to build a motorbike; simple, solid, reliable. This 350cc BSA B31 proves their strategy was spot-on. The B series of course went on to produce the likes of the legendary BSA Gold Star.

First registered 14 January 1957
Engine number BB311225
Frame number EB 316292
348cc, OHV, air-cooled 4-stroke single
Single 1-inch Amal carburettor
17bhp @ 5,500rpm
4-speed gearbox
3.25 x 19-inch front & rear tyre
Telescopic forks hydraulically damped
Rear swinging arm with twin rear shocks/dampers
3-gallon fuel tank
Full width 7-inch brake hubs
Lucas magneto
6-volt
Weight: 374lbs (170kg)
Top speed of 70mph (allegedly)

Our vendor tells us:

“It is an unmodified, never messed with, totally standard B31. The previous vendor fitted a handy ‘tap’ to stop it ‘sumping’. It runs well and nine times out ten starts first time. The owner before the guy I bought it from did all the work that makes it look the way it does today. I’ve done very little except potter around on it.”

BSA’s B31 is a star in the classic world. It seamlessly morphed from being ordinary day-to-day transport to becoming a classic. It is a testament to BSA’s approach that so many B31s rumble on still.

BSA’s first postwar model was the B31 A 350cc OHV single. It was based on designer Val Page’s 1940 B29 model.

Using the bottom end of the M-series side valve, it came with a cast iron barrel and an OHV head. The crank and roller bearing big end was lubricated by a dual gear oil pump.

The B31 clutch has a space within the primary chain-case to allow it to run dry. The case holds a small amount of oil. This is to lubricate the primary chain rather than the clutch itself.

The mid-50s saw real innovation on the B31, BSA introduced its own version of the new-fangled telescopic forks. These systems were transforming motorcycling.

External springs were fitted under the shrouds, plus hydraulic bump stops in compression. However, having no dampers on the rebound sometimes produced a disconcerting clang over sharp bumps. It was all part of the fun back then.

Versions of the innovative new system, without the accompanying clang, stayed on BSA machines for almost two decades.

The engine was robust enough to be turned into the B33 500cc by simply enlarging the bore. It went on to power B32 and B34 and, ultimately, the iconic Gold Star.

The B31 got the much-improved gearbox from the A-series twins too.

The Motor Cycle tested a rear sprung B31 in 1956.

“The bike started first kick and managed 73mph. The tester described the 105mpg at 40mph fuel consumption as remarkably good. You could tour on it at 60-65mph at half throttle, at which point vibration was perceptible through the dual seat”.

They finished by saying;

“The B31 is an attractive model for the rider who wants an easy-to-handle all-rounder but who is not insistent on a high maximum speed.”

The BSA B31 ran for 15 years. The later sprung models handle well, relative to the period of course, have better brakes and electrics, and are more reliable.

Summary

In the last five years, prices for BSAs have been trending upwards. This has something to do with scarcity of good ones as more classic riders want something easy to start and easy to live with.

A good one today will cost anything between £4,000-£6,000, depending on condition. Five years ago, you could buy one for half that.

Usable on modern roads and with more than a touch of class, the BSA takes life at a slower pace, However, it does have a large grin-inducing enjoyability factor.

If you are searching for a classic bike that is easy to work on, solid and fun, the B31 is a great option.

Vehicle Location: Hull, East Yorkshire HU9– it’s the responsibility of the winning bidder to make collection / transportation arrangements directly with the vendor

Have a question about this BSA B31? Please contact the Evoke team at team@evoke-classics.com and we will speak to the vendor on your behalf.