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Bike Review - Posted 20th March 2013
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Square Four Featherbed Special

Folk have been trying to fix the Ariel Square Four's flaws for donkey's years. One solution was to insert the engine into Norton's featherbed frame. An Arton special along those lines goes under the hammer at the Stafford Show...

Ariel's four-cylinder superbike was an astonishing machine in the pre-war era, and little less remarkable in its revised 4G format from 1948. Ariel boasted that the 997cc OHV machine was 'generally accepted as the world's most outstanding motorcycle' and they weren't too far from the truth. In every incarnation the Square struggled to master its mass and suffered from overheating (on the rear pair of cylinders in particular), but there were few motorcycles which could effortlessly ooze up to 90mph in 1950...

The postwar Square engine was extensively redesigned for 1948. It swapped to coil ignition and the cast iron block and cylinder head were replaced by alloy items which trimmed the machine's mass by around 35lb. This reduced its weight to 'only' 435lb which was still rather more than the plunger-style rear suspension could cope with.

Astonishing indeed, in its day... Ariel's original take on the Square Four

The engine ran at 6:1 compression as standard, although 6.8:1 pistons were offered if owners could find petrol of a suitable quality to match. This gave around 35bhp at a relaxed 5500rpm, transmitted to the rear wheel via a three-plate dry clutch and four-speed gearbox to the drive chain.

Braking was a little less confidence inspiring: the rear 8-inch brake was considered 'powerful' for its time but the front full-width alloy stopper was useful mainly for carefully considered slowing rather than outright emergency stops.

The roadtesters of the time reported finding the Square's 'combination of zestful performance and the roly-poly handling diverting and, on the whole, congenial.' My own experience of riding a plunger Square was rather less enjoyable: it honestly felt as if the rear end of the machine had a mind of its own, squirming around even when we were travelling in as straight a line as proved possible, and I couldn't give it back to the owner fast enough. However, in the 1950s most riders used the Square for sidecar duties or long distance touring, where its top quality detailing, specification and comfortable ride were rather more important than razor-sharp steering or stopping.

Yet it was obvious that the Square really needed its suspension sorting out. Ariel themselves experimented with Earles forks but didn't get beyond prototype phase. The company then swapped to two-stroke production, and so the task of perfecting the Square fell to owners, enthusiasts and engineers.

Colour was rationed in the 1970s, due to the three day week... Healy 1000/4

In the 1970s the Healey brothers created a short run of swinging arm, twin-shock Squares, initially using an Egli rolling chassis. Their 1000/4 used a spine frame with taper-roller head bearings and needle rollers for the rear, with two-way damped Ceriani forks at the front and adjustable Girling shocks at the back.

See what they did with the logo?...
Ariels on

The Healey brochure claimed that it offered the 'electric response necessary for fast line chopping… precise steering… and unwavering line during the accelerating keel into speed' and cornered 'faster than most… safer than most.'

Looks like it's meant to fit there... Graham Horne's Square Huntmaster

More recently, marque specialist Graham Horne used his experience from working at the Ariel factory to develop his own swinging arm version of the Square. This employed Ariel's own swinging arm chassis as seen on the 650 Huntmaster twin. A four-pipe example of one of Graham's SwingSquares sold a couple of years back at Bonhams for a whopping £11,500 - mind you, it was in very tidy condition, as you can see from the photo hereabouts, and had only travelled a few hundred miles since its build.

Requires a double-take.. Arton: 1952 Ariel square Four in a 1960 Dommi 99 featherbed chassis

There was, of course, another option open to Square Four enthusiasts back in the day. Norton's featherbed frame can be adapted to suit all manner of weird and wonderful projects, and not just the usual Triton specials. In this instance, a 1960 Dommi 99 featherbed chassis was matched - with some accomplishment - to a 1952 Square engine, to create (if you must) an Arton.

Shoe-horn not required..

The owner, now deceased, collected parts for his special throughout the 1960s, and the finished article took to the tarmac for the first time in the 1980s. It was then used through to the end of the 1990s but has been stored for the last 15 years or so. It comes with its old MoTs, V5C and such, but would obviously need a once-over with the spanners before being ridden any distance.

Marvellous detailing..

The price for such an unusual beast? Bonhams reckon between £7000 and £9000, but I wouldn't be surprised to see it sneak into five figures. After all, while you can buy a new featherbed fame these days, Square Four engines are rather harder to come by. This isn't the most sought-after four-pipe motor, but it is a nifty little creation blessed with decent brakes. It'd be very interesting to see how well it steers (so if you buy the thing, do let me have a spin!)

Words: Rowena Hoseason
Photos: RC RChive,


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