Ariel Square Four 4G
Probably the world’s most experienced motorcycle journalist comes away impressed from his first ride on a motorcycle made for a certain type of riding.
It’s become a cliché to describe MV Agusta as the Ferrari of two wheels, with each marque dominant in its own form of Grand Prix racing, and presided over by an autocratic despot. Likewise its Benelli rival as the Maserati of motorcycles, each the product of the impecunious but passionate endeavour of a band of brothers. But in Britain there’s a couple of comparable analogies, with Triumph so very much motorcycling’s equivalent of its close neighbour Jaguar, thanks to its sporty Speed Twin and later Bonneville derivatives, while the fast, luxurious Ariel Square
Four – of which this year is the 90th anniversary of its showroom debut in 1931 – is perhaps a two-wheeled Aston Martin. Moreover, there’s a further connection between these two legendary models in that a single man was responsible for creating each of them:
Edward Turner.
Turner would later become the most powerful figure in the British motorcycle industry, but in 1927 during the peak of motorcycling’s post-First World War boom years, he was an impoverished 26-year old former merchant seaman who’d become a Velocette dealer in Peckham, South East London and, without any formal engineering training, had designed a 348cc singlecylinder OHC engine.
He went through various means of driving its camshaft, but ended up with a vertical shaft and bevel gears for an engine powering a motorcycle of his own construction, the Turner Special. Though Turner advertised it for sale through his small Chepstow Motors shop, the £75 asking price was pretty steep, and it’s unlikely he found any buyers – certainly, no such bike has survived the passage of time. This was despite several articles about the design having appeared in print, and it was as a result of one of these that in March 1927 the Birmingham-based Ariel marque’s dynamic sales and promotions manager, Vic Mole, visited Turner’s shop to discuss it with him. He left unimpressed by the 350cc single, but enthused by another quite different concept Turner had outlined to him, but which so far he hadn’t progressed beyond a rough outline – a 500cc OHC square-four motor.
Mole reported back to Ariel owner Jack Sangster, one of the most astute figures in the history of the British motorcycle industry, who invited Turner to visit the company’s Selly Oak factory. There, Turner duly convinced Sangster of the viability of his innovative square-four design in overcoming the disadvantages of a car-type inline four which, when mounted transversely, was unduly wide, and when disposed lengthways in the frame as in the contemporary AJS
630cc prototype, or an American Henderson or Ace four, resulted in an excessively long wheelbase, as well as handling issues caused by the inertia forces of the longitudinal crank. After some discussion, Sangster agreed to give Turner an office at Selly Oak to draw up the square-four engine properly, as well as an assistant to help him do so – none other than Bert Hopwood, who, 20 years later, post-Second World War would design the Norton Dominator, arguably Turner’s parallel-twin Triumph’s greatest rival.
The two began work in November 1928, and what emerged in public two years later was a unit-construction 500cc square-four design with a horizontally-split crankcase, and twin crankshafts geared together via helical teeth cut into the central flywheel of each crank assembly, in what essentially represented a pair of parallel-twin engines mounted in tandem.
Turner specified a chain-driven single overhead camshaft, with a single front-mounted Amal Type 74 carb, and just a three-speed gearbox in recognition of the engine’s broad spread of power peaking with 22bhp at 6000rpm, with the drive to said gearbox taken from the specially extended left-hand end of the rear crankshaft.
The prototype motor was so compact it could be mounted in the lightweight frame used for the company’s 250cc Colt single, but by the time the Ariel Square Four Model 4F was unveiled at London’s November 1930 Olympia Show, the engine had been transferred to the more robust chassis used by Ariel’s 500cc SG31 Sloper single, after being subtly redesigned by the firm’s chief engineer, Val Page, to be less costly to manufacture, as well as more rational in design. This included installing a separate hand-change four-speed Burman gearbox, with chain primary drive.
The Ariel Square Four caused a sensation at the Show, despite sharing the limelight with the Matchless Silver Hawk with its compact narrow-angle V-four engine, although at £75.10.0, the Ariel scored on price, and would remain in production far longer in various guises, until 1959.
Deliveries of the first of the 927 examples sold in the initial two years of production began in April 1931, and magazine testers gave the ‘Squariel’ – as it was inevitably christened! – favourable reviews in praising the smoothness and flexibility of the 498cc wet sump engine measuring 51x61mm, which from 0-30mph was shown to be only 0.4sec slower than an eight-litre Bentley saloon car. Furthermore, to underline how easy it was to start, Vic Mole arranged for seven schoolboys aged 12-14 to kick-start the new Square Four seven times each. Of the 49 attempts it started first kick 48 times, and only once took a second attempt to do so!
Turner had left space in the one-piece cast iron cylinder block to permit a 5mm overbore for 1932, which produced a 601cc Model 4F6 aimed at sidecar use delivering 24bhp, and now with straight-cut teeth for the coupling gears. Of this 600cc version, 2674 would be built, but later in 1932 Ariel’s Carbodies
Ltd parent company went bankrupt, mainly thanks to the insolvency of its Swift car division managed by Carbodies MD/CEO Charles Sangster, Jack’s father. But Sangster Junior was convinced of Ariel’s viability, and duly injected his own capital into the firm by purchasing its assets from the liquidator, re-establishing the company as Ariel Motors (JS) Ltd and installing Edward Turner as chief designer to replace the now departed
Val Page.
Workforce numbers were slashed, and the majority of the Selly Oak factory’s ground area leased out, as
motorcycle production shrank into one small section of the premises, and the range of models was reduced. But perhaps surprisingly, given the austerity of the times, the costly, range-topping Square Four survived the cull and remained in production, despite early examples suffering from insufficient cooling of the rear part of the cylinder head, resulting in frequent blown head gaskets. For 1933, a four-speed foot change gearbox was introduced.
To resolve the ‘cammy’ 4F6 engine’s overheating problems, and to deliver the missing torque needed to lug a well-laden sidecar, in 1936 the Square Four motor was completely redesigned, with the OHV 995cc Model 4G emerging as a smoothly tuned super tourer which Ariel claimed would accelerate from 10mph to 100mph in top gear – and just to prove it, paid Brooklands rider Freddie Clark to do so in 1936. Meanwhile, Jack Sangster had acquired the bankrupt Triumph concern’s motorcycle division 25 miles away in Coventry, installing Turner there as chief engineer, so although he’d been responsible for creating the heavily revised one-litre Square Four, it was his successor at Ariel, Frank Anstey, who saw it through to production.
The new OHV engine measured 65x75mm, with short pushrods replacing the camshaft in operating the valves sitting in pent roof combustion chambers delivering a low 5.8:1 compression ratio. The crankcase was now vertically split and the engine consequently dry-sumped, with the all-new crankshafts that were widened to run in timing side bushes and drive side roller bearings, carrying forged RR56 aluminium conrods via plain white metal big end bearings, with cast aluminium three-ring pistons. The two crankshafts were now coupled by spur gears on the left-hand drive side of the engine, with a single-strand primary chain leading to a dry clutch, and a four speed foot-change Burman gearbox.
The 601cc cammy was discontinued (although a 599cc OHV version was announced for 1939) while the larger OHV version, which put out 38bhp at 5500rpm, was immediately successful. A total of 4288 examples of the Model 4G were sold between 1937 and 1948, latterly with a unique form of rear suspension available as a 1939 option, albeit at a 22lb penalty in weight. The socalled Anstey link (named after its designer) was a form of plunger suspension, but with pivoted links which allowed the rear wheel to travel through an arc, giving constant chain tension for enhanced chain life as well as a more comfortable ride, despite the springs in the plunger boxes having no form of damping. Both 600cc and 1000cc versions dispensed with Amal carburettors in favour of a rear-mounted Solex 26FHDT unit.
When peace returned, motorcycle production at Selly Oak saw manufacture of the Square Four restart in 1946, but in 1000cc form only with an oil-damped telescopic fork replacing the Webb-type girder fork used hitherto, and the plunger rear end now included as standard. But under the British Government’s ‘Export or Die’ push production was primarily destined for the USA, where cube-conscious customers appreciated the Ariel four’s torquey nature and appetite for speed that was so smoothly delivered. Indeed, one of them, Pasadena, California dealer Bill Johnson, had examined a Square Four parked in the street one day in 1939 and was so intrigued by it he imported one for himself, followed by several more for other local enthusiasts. This in turn led to him establishing a long distance friendship by letter with Edward Turner, which at the end of hostilities resulted in Johnson Motors becoming the Western US importer for Ariel and Triumph, selling thousands of bikes through the 1940s-60s boomtime for British motorcycles in America.
In 1949, the Square Four engine was redesigned as an all-alloy power unit now fitted with a car-type SU variable choke Type MC2 carb which, being rather tall, the frame had to be modified to accept. The cast iron cylinder block and cylinder head were replaced by narrower and lighter aluminium parts, which resulted in a 33lb weight saving, while the head was redesigned internally to improve breathing, and now fitted with 20 fixing studs rather than 12 to combat its predecessor’s head gasket leaks. But at 434lb (197kg) dry the rechristened 4G Mk.I model with plunger rear end was no lightweight, making the 35bhp at 5500rpm delivered by the revised engine seem rather underwhelming.
With its rather small valves, a pretty constricted inlet tract, low 6:1 compression ratio to take account of lowoctane pool petrol, and those pent-roof combustion chambers, this was only to be expected, and the main thing as far as customers were concerned was the motor’s smooth delivery and lashings of torque, with a top speed of 95mph. It was a true gentlemen’s express, as evidenced by the succession of Ariel adverts for the bike all through the 1950s depicting chaps with tweed jackets and jodhpurs, or blazers, slacks and a cravat scarf, who presumably were Ariel’s target clientele. Well, maybe it was a two-wheeled Aston Martin, after all! But whatever the case, 3922 new owners were found for the Mk.I model in just four years, up to 1953 and the arrival of the 4G Mk.II version.
In 1951, Jack Sangster sold Ariel and Triumph to the BSA Group, whose board he also joined and from 1956 onwards headed as chairman, having defeated the egregious incumbent Sir Bernard Docker in a directors’ vote. Sangster promptly made Edward Turner head of the company’s automotive division, which then included Ariel, Triumph, and BSA motorcycles, as well as Daimler and Carbodies, builder of London Taxicabs. Under BSA Group ownership Ariel had, publicly at least, remained in charge of its own destiny, and the Square Four was again the subject of another major redesign in 1953 to produce the Mk.II version – the ultimate incarnation of Turner’s original design, now fitted with a bench-type dual seat replacing the previous sprung solo saddle and separate pillion pad.
The revised engine featured a new exhaust system, with four separate header pipes for the first time, two on each side, which emerged from handsome polished cast-aluminium manifolds and curved downwards to join a single silencer on each side. With higher quality fuel now becoming available, compression ratio was lifted to 7.2:1, and power raised to 42bhp at 5800rpm. The alloy rocker box was now combined with the inlet manifold, and carburation now came via a variable choke MC2 SU carburettor.
However, despite the mid-1950s creation of a prototype new frame with swinging arm rear suspension and a leading link fork, the Square Four soldiered on with the elderly plunger/link design, and would do so until
it reached the end of its production in 1959, by which time a total of 15,639 examples of all the different Square Four models had been built in the 28 years since 1931. With 600 or so examples still sold each year of a unique high end model with no direct competitors, which had had its development costs written off several times over, it was a curious decision which came about as a result of BSA Group management terminating manufacture of all Ariel four-stroke models, in favour of a new wave of two-strokes headed by the Val Page-designed twincylinder Leader and its ilk. And to demonstrate just how astute a decision that had been, Ariel motorcycles ceased production in 1967.
Sammy Miller had a particular reason for seeking out the second of the two Ariel Square Fours in his eponymous Museum www.sammymiller.co.uk in England’s South Coast, for alongside the 600cc example on display built in 1936, the former trials ace was eager to acquire one of the very last Mk.II 995cc models built from 1957 onwards. “That’s when I joined the Ariel factory’s Competition Department,” says Sammy. “I’d had to wait until after the Italian GP in September when my road racing contract with the works Mondial team would be over. After that I didn’t have many spare weekends, because I’d be competing in either trials or road racing practically all year round. But if I did have a weekend off I’d always try to arrange to borrow a Square Four from the factory test fleet – it was such a wonderful bike to ride, and I was really disappointed they stopped making them about a year after I joined. So when we started the museum, I was on the lookout for an original example of one of the last Mk.II models – and in 2012 we finally found this one.”
Bearing engine no. CNML 2063 in chassis no. CCM 2032, and with an almost certainly authentic 18,479 miles from new on the Smiths Chronometric speedo, 709 AFD was first registered on April 21, 1960, having been sold new by Frank Cope Motorcycles in Birmingham to a Mr J K RiceJones in Moseley, less than three miles as the crow flies from Ariel’s Selly Oak factory. It may possibly have been a display model which Ariel kept in the factory foyer until the model was discontinued, and therefore needed to be sold via a friendly local dealer – but that’s just conjecture. Rice-Jones kept the bike for almost two years before selling it to a Mr Joseph Gregory in Hitchin, Herts, who kept it until he passed away in 2011, whereupon Sammy bought it from his family. “They were eager to tell me that the bike had never been ridden in the rain, which in Britain would be an amazing achievement!” he says. “But it’s completely original and has that lovely patina of use, so though I ride it quite often, I try to make sure it’s still kept dry!”
Having been almost ashamed to admit that I’d never previously ridden a Square Four, with the sun beating down on the New Forest lanes around the museum and rain not in the forecast, Mr Miller sent me off for an afternoon ride around the Hampshire countryside on a bike that, who knows, he might very well have ridden in 1959.
During my ride, I became even more convinced what a strategic mistake the BSA Group management had made in discontinuing this model when they did. It’s easy to start even with the slightly higher
6.7:1 compression of the Mk.II version, and settles to a slightly fast idle, with the 180° cranks delivering a slightly buzzy engine note that sounds rather like a syncopated version of two BMW Boxer twins slightly out of kilt with one another.
The one-up right-foot gearchange is smooth and quite precise, same as the light-action dry clutch which makes the Squariel very easy to ride in traffic. But you honestly don’t need to change gear very much because of the smooth – that word again! – and syrupy power delivery, which isn’t so much muscular as understatedly insistent. It almost doesn’t matter what gear you throw at it, unless you’re really in a hurry, and even then, revving the vibration-free engine to something approaching the redline – there’s no rev-counter fitted – doesn’t really get you places any faster than just riding the torque curve, and going with the flow. I didn’t try to copy Freddie Clark and go from 10mph to the ton in top gear, but I did get to 60mph from that low, without a hint of transmission snatch.
What a revelation sampling a Squariel must have
been to riders accustomed to riding shaky singles or tingling twins – for all the clichés about a magic carpet ride apply here in spades.
However, that’s just the engine, which over a decade after BSA terminated it could have provided a perfectly valid British answer to the Honda CB750 four. The one-litre Square Four motor has significant reserves of performance just waiting to be unlocked, and failing to do so was a massive lost opportunity by the BSA Group.
But they’d have had to do something about the chassis to harness that performance, because the behaviour of the Miller Museum’s original example over bumps and broken road surfaces wasn’t the greatest, with what felt like minimal wheel travel from the plunger rear end. It also understeered slightly on faster bends, though that was probably down to the combination of wheel sizes and tyres, with the 19-inch front shod by a ribbed Avon Speedmaster against the 18-inch rear’s block-treaded Avon SM.
Even so, I was occasionally able to discover the limitations in ground clearance of what is quite a low-slung motorcycle. The full width seven-inch front drum brake had a nice bite from what was probably still the original brake shoes. The riding position was quite spacious, with the 30in seat height and slightly rearset footrests giving a comfy stance that makes you feel at one with the bike. Nice.
After finally losing my Squariel virginity, I remain convinced that this largely unsung motorcycle is a great British success story that for one reason or another has never had the due recognition it deserves. Maybe it’s because Ariel didn’t go road racing, so wasn’t considered an illustrious marque in the same way as
BSA or Triumph was. But this lovely motor – which by the way, nobody ever succeeded in copying, or more likely never even bothered trying, in which case, more fool them – has so many advantages compared to the inline fours which became ubiquitous, not least its compact build and complete lack of vibration, with only the overheating issue to resolve, which liquid-cooling it would easily do. Edward Turner was a very clever man, and this motorcycle is further definite proof of that.