Smooth and steady all-rounder
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
An A65 As We Wanted It
Jim and Liz knew just how they wanted their A65 Lightning to be
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…
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!
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...
Behind The Scenes Heroes The CRMC Scrutineers
With a variety of machinery to check, can we learn from the CRMC scrutineers?
These Italian/American bikes have a lot to offer, and they don’t cost a fortune
Sporting sophistication for clubmen and commuters
Sure-Footed Shooting Star
Smooth and steady all-rounder
Utterly In Zane?
As a bargain-buy, high-performance classic, Laverda’s 750 superbike makes a strange kind of sense
It’s not a Nomad by name, but this Norton tourer has clocked up a quarter-million miles anyway
A Royal Enfield Indian disruptor from J. Shia’s Madhouse
BRITISH SPORTING ART TRUST
John Ferneley Senior in his Studio at Elgin Lodge, Melton Mowbray by Claude Lorraine Ferneley (1822-1892)
गलवान के नायक कर्नल संतोष बाबू को मरणोपरांत महावीर चक्र
झड़प में शहीद हुए चार अन्य सैनिकों को वीर चक्र से नवाजा गया
THE BIG TEST - ON THE FIRING LINE THIS MONTH:HATSAN SPEEDFIRE
Dave Barham tests the new 10-shot break-barrel repeater from Hatsan
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.
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.
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.
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
Hotter Rockets Launched For 2020
The world’s largest-capacity volume production motorcycle just got bigger.
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