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This 398cc motorcycle
had a smooth transverse flat-twin engine. In production from 1920-1923,
the ABC has overhead valves, wet-sump lubrication, a four-speed gearbox,
drum brakes and full suspension.
Granville Bradshaw designed the motorcycle for the All British (Engine)
Company, including in his design stable-handling, a superb wide-duplex
frame and tubes that acted as crash bars for the cylinder heads.
Unfortunately, the engine design needed more development.
Valve gear was weak, the kickstart was prone to jamming, and the long
induction tracts iced up until they were modified.
The makers of the bike, Sopwith Engineering went bust in 1920 and
production was taken over by Jarvis and Co. after
2,200 had been sold. French Engine Manufacturer Gnome et Rhone made
the ABC under license and enclosed the valvegear, redesigned the crank,
improved lubrication, fixed the kickstart and built a 493cc version.
They continued to produce the ABC until 1925.
The ABC used laminate leaf springs to control the movement of a girder
front fork. Granville Bradshaw did break the boundaries when he applied
a spring type normally used only on cars. Bradshaw was inspired by
the Indian cradle spring frame rear suspension, introduced in 1913.
Bradshaw anchored both ends of the springs firmly, rather than allowing
one end to pivot. This meant that under deflection, the springs were
forced into a flattened 'S' shape, which brought about a self-damping
effect. Combined with the low weight it produced a very supple ride.
The braking system on the ABC consisted of a 152mm drum on the front,
and a 178mm at the rear. Although this wouldn't impress today's riders,
for it's time it was quite advanced.
Technical
Production : 1920-1923
Engine Type : Transverse
flat twin, air cooled, pushrod, 2 valve, 4 stroke.
Capacity : 398cc
Bore and Stroke : 68.5
x 54mm
Compression Ratio : 5.5:1
Fuel System : 25mm
Claudel Hobson carburettor
Power : 9PS
Dry Weight :
80kg
Top Speed : 60mph
| Comments |
| Hugh 5th March 01 | Thank you for the wonderful article on the ABC. It is very informative and interesting, it has helped a great deal with my university project.
| | herman eric u. segovia 28th July 02 | what's the difference between a flat-twin engine and an axially aligned opposed piston engine
| | amy bradshaw 2nd March 03 | thank you for this article...it helped me to understand more about the motorbike that my great grandad helped to create.
| | Jochen Kraus 16th April 03 | Thank you for this Article,
I´have got a question my neighbour has this ABC with the number 1 on the engine. How much should i pay for this bike? How many were built
| | Howard Burrows 2nd June 03 | Thanks for the info. I have not been able to find much on ABC on the web. I have a 1920 French model and 2 UK built machines. I have enough spares to build another French model if I had a frame.
Always interested in talking ABC's......please email flattank@bigpond.com
Thanks.
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