Big-Hearted Beezer: BSA/Ariel “Flash Four”

Nestling an Ariel Square Four engine into a BSA A10 Golden Flash frame creates the “Flash Four.”


1957/1949 BSA/Ariel "Flash Four"

Engine: 997cc OHV air-cooled Square Four MkI, 65mm x 78mm bore and stroke, 6:1 compression ratio, 35hp @ 5,500rpm
Top speed: 90mph
Carburetion: Single Solex 26 AHD
Transmission: Chain primary, BSA multiplate clutch, BSA 4-speed gearbox
Electrics: 12v, battery/coil with distributor
Frame: BSA A10 Golden Flash dual downtube full cradle, modified
Suspension: BSA Telescopic fork front, two coil spring/damper units rear
Brakes: BSA/Triumph 8in (203mm) TLS drum front, 7in (178mm) SLS drum rear
Tires: 100/90 x 18in front, 110/90 x 18in rear
Weight (wet): 400lb (182kg)
Seat height: 32in (813mm)
Fuel capacity/MPG: 4.2gal/55mpg (est.)

It’s a situation familiar to many motorcycle wrenchers: In one corner of the garage is a frame left over from a previous project, and hiding under the proverbial workbench is a similarly orphaned engine.

In Lyle Whitter’s case, the engine was a 1949 alloy two-pipe Ariel Square Four Mk1, and the frame was a 1957 BSA A10 Golden Flash. And the question uppermost in Whitter’s mind: would the two go together?

The eventual answer was … yes — but not without some considerable workshop skill and patience.

The engine

The engine that Whitter used for his BSA-framed custom bore little resemblance to Edward Turner’s original design — except for the “Square Four” cylinder layout.

1/14/2021 8:16:43 PM

Unlimited admiration for Lyle's work - the bike that BSA/Ariel could have built at the time.....except the later front brake. Great to see such cooperative craftmanship in action. I hope they had some 'young blokes' looking on and helping, it would be a huge loss if these abilities just disappear, as seems highly likely.

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