CarBrandLogos archive · BSA · 1946

BSAA7

BSA's answer to the Speed Twin, and the foundation of its post-war twin-cylinder range.

Photo: Yesterdays Antique Motorcycles · CC BY-SA 4.0

The story

A defining chapter in BSA history.

Explore the ideas, engineering and context that shaped the BSA A7, then continue into its specifications and place in the marque's lineage.

Origins

Triumph's Speed Twin of 1937 had changed what British buyers expected, and every rival needed a parallel twin of its own. BSA's arrived in 1946, a 495 cc unit designed under Herbert Perkins with input from Val Page, built at Small Heath and aimed at riders who wanted more smoothness and speed than a big single without the maintenance burden of a complicated engine.

BSA A7SS Shooting Star · SG2012 · CC BY 2.0

Design and engineering

The early bikes used a duplex primary chain to a four-speed gearbox bolted to the rear of the crankcase, a semi-unit arrangement that made the engine compact. When swinging-arm frames arrived the layout changed to a single-row primary chain and a separate gearbox. The A7 was redesigned by Bert Hopwood at the end of the 1940s, becoming the basis of the larger A10 that followed.

BSA A7 Star Twin · SG2012 · CC BY 2.0

In production

Its reputation was built on reliability rather than outright pace. A team of A7 Star Twins completed a long-distance European endurance run and an ISDT campaign that BSA advertised heavily, and the model sold steadily in Britain and America until 1962, when the unit-construction A50 replaced it.

At a glance

The facts that define it.

Produced

1946–1962

Engine

495 and straight twin

Technical specification

The A7, in detail.

Production: 1946–1962
Engine: 495 and straight twin
Transmission: Duplex primary chain to 4-speed gearbox, bolted to rear of crankcase; Single-row primary chain to separate 4-speed gearbox (swinging arm models)
Assembly: Small Heath, Birmingham England
Manufacturer: BSA

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