Sure-Footed Shooting Star
Classic Bike Guide|June 2017

Smooth and steady all-rounder

Marion Thirsk

DEVELOPED DURING THE late 1930s, BSA’s first parallel twin was launched in 1946. Triumph’s 500 Speed Twin may have been faster but the A7 quickly gained a reputation for being quieter, dependable and significantly more oil tight. Proving popular, the A7 was given one significant revamp and then continuously tweaked and improved throughout a 16-year production run.

The early A7 twins featured a cast iron cylinder head and block with a bore and stroke of 62mm by 82mm to give 495cc, reaching 27bhp at 5800rpm. At a time when most manufacturers were using twin camshafts, BSA cut costs with a gear-driven single camshaft operating overhead valves via four pushrods. Two separate aluminium alloy rocker boxes were fitted with Edward Turner-influenced screw caps. A neat ‘semi-unit’ gearbox was bolted to the rear of the crankcase with primary chain tensioning achieved by means of a curved slipper tensioner. This was adjusted by a screw-in bolt with a lock nut. Both wheels were quickly detachable. The early, longer stroke single carb A7 engine lasted four years, with a sports variant, the higher compression twin carb A7 Special (soon renamed the Star Twin with plunger frame) enjoying a power increase to 31bhp at 6000rpm.

BSA introduced an all-new A10 650 twin late in 1950, designed by industry stalwart Bert Hopwood. A new version of the A7 followed shortly after and featured a redesigned engine based solidly on the A10. Outwardly the engine was similar to the earlier A7 but improvements had been made within. Changing the bore and stroke to 66 by 72.6mm increased the engine capacity to 497cc. There was no particular increase in outright power but the shorter stroke engine is considered smoother than both the A10 and the earlier long-stroke A7. The new A7 used the same single Type 6 Amal carb as its predecessor. The electrics were changed over to positive earth and a trough was added below the camshaft to retain oil, providing vital lubrication to the cams even if the engine was laid up for long periods. A one-piece rocker box was introduced, making reassembly fiddly and difficult. BSA provided a special ‘comb’ tool which is helpful when attempting to keep the pushrods in place in the rocker ends when refitting the rocker box but it is still very awkward.

Continue reading your story on the app

Continue reading your story in the magazine

MORE STORIES FROM CLASSIC BIKE GUIDEView All

An A65 As We Wanted It

Jim and Liz knew just how they wanted their A65 Lightning to be

10 mins read
Classic Bike Guide
December 2019

Norton Atlas 750

Hutch’s Norton Atlas 750 has been a good, solid workhorse – until some journalist had a little go on it and the clutch broke…

2 mins read
Classic Bike Guide
December 2019

National Motorcycle Museum Live 2019

Getting more people to come to a museum must sometimes seem like a tricky affair, but the National Motorcycle Museum does it brilliantly. They let you in, for one day only, for free!

1 min read
Classic Bike Guide
December 2019

Coventry Eagle Flying 8

The little-known range topper of everyman bikes manufacturer, Coventry Eagle, has been a larger influence on biking than you may have thought. Rachel Clegg investigates...

7 mins read
Classic Bike Guide
December 2019

Behind The Scenes Heroes The CRMC Scrutineers

With a variety of machinery to check, can we learn from the CRMC scrutineers?

4 mins read
Classic Bike Guide
December 2019

Aermacchi Harley-Davidson

These Italian/American bikes have a lot to offer, and they don’t cost a fortune

10+ mins read
Classic Bike Guide
December 2019

Verdant Velo

Sporting sophistication for clubmen and commuters

5 mins read
Classic Bike Guide
June 2017

Sure-Footed Shooting Star

Smooth and steady all-rounder

5 mins read
Classic Bike Guide
June 2017

Utterly In Zane?

As a bargain-buy, high-performance classic, Laverda’s 750 superbike makes a strange kind of sense

5 mins read
Classic Bike Guide
June 2017

Desert Stormer

It’s not a Nomad by name, but this Norton tourer has clocked up a quarter-million miles anyway

4 mins read
Classic Bike Guide
June 2017
RELATED STORIES

Devil's Advocate

A Royal Enfield Indian disruptor from J. Shia’s Madhouse

3 mins read
Cycle World
Issue 3 - 2020

BRITISH SPORTING ART TRUST

John Ferneley Senior in his Studio at Elgin Lodge, Melton Mowbray by Claude Lorraine Ferneley (1822-1892)

1 min read
The Field
May 2021

गलवान के नायक कर्नल संतोष बाबू को मरणोपरांत महावीर चक्र

झड़प में शहीद हुए चार अन्य सैनिकों को वीर चक्र से नवाजा गया

1 min read
Hindustan Times Hindi
January 26, 2021

THE BIG TEST - ON THE FIRING LINE THIS MONTH:HATSAN SPEEDFIRE

Dave Barham tests the new 10-shot break-barrel repeater from Hatsan

5 mins read
Air Gunner
October 2020

Cybercrime has risen during COVID-19: here's how to stop it

The ASEAN region has been living with the novel coronavirus that causes COVID-19 for several months now, and different countries are at different stages of crisis.

3 mins read
Gadgets
June 2020

Third Time Lucky

Will this third BSA side-valve single measure up to the first one? Should you ever go back? Yes, of course you should if it provides a spark of joy.

9 mins read
The Classic MotorCycle
August 2020

Gone But Not Forgotten

I intend this to be an infrequent series on a selection of the hundreds of motorcycle manufacturers that have long since disappeared, whether they had been in production a year or two or a few decades. Some possibly deserved to wither and die, while some were very successful but still went out of business; some have faded from memory but many are remembered. They are all part of the rich tapestry of the history motorcycling.

3 mins read
Bike SA
July 2020

Keeping Disaster at Bay

An emergency rescue team in Morecambe Bay have rescued scores of people and now have state of the art kit that could save even more lives

5 mins read
Lancashire Life
May 2020

Hotter Rockets Launched For 2020

The world’s largest-capacity volume production motorcycle just got bigger.

4 mins read
Triumph World
December 2019 - January 2020

TANGLED UP IN BLUE

There are some bikes which become inextricably linked with their owners to the point where it’s almost impossible to imagine them in the possession of anyone else and yet which also stick in people’s memories even though they might not be the most radical of custom bikes

3 mins read
100% Biker
Issue 254