ARIEL SLOPER 6
Is a sloper engine more than just a passing fashion? Alan Cathcart investigates a handsome Ariel…
Is a sloper engine more than just a passing fashion? Alan Cathcart investigates a handsome Ariel…
Few other Vintage-era British manufacturers offered as extensive or as varied a range of motorcycles in the late 1920s as Ariel, one of the pioneer brands in two-wheeled history, which was by then part of the Components Ltd group owned by the Sangster family. Charles Sangster had purchased Ariel back in 1902, but it wasn’t until his son Jack – who’d duly prove to be one of the most astute management figures ever in British motorcycle industry annals – took over running the company after WW1 that the Birmingham-based marque really began to flourish.
This especially came after Val Page joined it in 1925 from JAP as Chief Designer, then from 1926 onwards produced a flow of good-selling new models powered by Ariel’s own engines of his creation. Previously, Ariel had used proprietary motors from the likes of Blackburne, JAP and even Swiss concern MAG. This exciting array of ground-up new models prompted the company slogan ‘Ariel – The Modern Motor Cycle’, and resulted in Ariel selling 19,000 machines in the first eight months of 1929, before that September’s London Stock Exchange Crash changed what was then the world’s largest motorcycle industry for ever.
Sangster responded to the ensuing 1930 downturn in sales by swimming against the industry tide. Most of Ariel’s competitors which managed to survive did so by drastically pruning their ranges, and by concentrating on budget-priced bikes with limited performance. But Sangster on the other hand commissioned Page to develop an eight-model single-cylinder line-up for 1931, ranging from the three 250cc Colt models to the 557cc sidevalve sidecar tug, with a quartet of 500cc machines in between. This was unveiled in October 1930, just ahead of London’s Olympia Show, together with a
ninth range-topping model in the shape of the Square Four, which had been created by Page’s notional subordinate Edward Turner. He’d been recruited three years earlier by Sangster to do just that, and would later head up Triumph after Sangster acquired that bankrupt concern’s motorcycle division in 1936. Ironically, Page had left Ariel in 1932 after the company’s brush with bankruptcy – to become chief designer at Triumph!
Val Page’s 1931 quartet of half-litre dry sump OHV Ariel singles all employed the same bottom end and four-speed Burman BA-PDH hand-shift gearbox with an enclosed oil-bath chain primary, but with a choice of different top end configurations according to customer choice, and budget. The VB31 was a vertical cylinder single-port model with a two-valve cylinder head, while the VF31 was the same bike, but with a four-valve head.
These were essentially reworked versions of the existing 1930 models – but the two new Sloper 500cc variants (plus the SB31 557cc sidevalve) broke new ground for Ariel in somewhat belatedly seeking to climb onto the same slanted cylinder bandwagon that its near neighbour BSA – the Ariel Works, backing on to Cadbury’s Bourneville chocolate factory, lay just five miles away from BSA’S massive Small Heath plant – had set in motion by unveiling its own Sloper model in 1927, which would remain in production until 1935.
The new Ariel SF31 two-valve model selling for £55 and its SG31 four-valve counterpart priced at £60 were both twinport models, with graceful exhausts running back to a pair of Art Deco-style fishtail silencers. But the standout design feature on each bike was its steeply raked cylinder, inclined forwards at 60° from vertical – double that of the BSA which had evidently inspired it, and sufficiently pronounced for Ariel to justly claim this to be more than just a simple styling feature. The Sloper format delivered a notably lower centre of gravity, resulting in improved handling, especially over bumps, as well as better accessibility for maintenance and enhanced engine cooling, further aided by the longitudinal finning on the cylinder barrel, and radial finning on the cylinder heads.
The 498cc Sloper OHV engines were described in Ariel’s brochures and advertising as ‘Specially tuned for high speed work’ with ‘Highly polished valve ports’ and ‘Inlet valve guides lubricated by suction from crankcase’. The use of an aluminium piston would have helped reduce inertia and make the engine spin more freely, while both two- and fourvalve versions were unfashionably oversquare for the times. Their dimensions of 86.4 x 85mm, while today apparently very modern, in fact represented a return to the bore and stroke measurements used on the immediate pre- and post-ww1 T-head sidevalve Ariels.
Their pushrods were enclosed in separate tubular cases with oil-tight rubber seals at their bottom ends, and were actuated by the single camshaft driven off a half-time pinion from the crank. The cams used the same profiles later fitted to Ariel’s longlived sporting Red Hunter model, which was Val Page’s farewell present to the firm, debuting in 1932 just before his departure. Twin exposed coil springs were fitted to each valve, while the rockers running on roller bearings were fully enclosed in a cast aluminium rocker box, and lubricated by grease gun.
All the Slopers had double roller big ends, and ball race main bearings on each side of the vertically-split crankcase. A doublegear oil pump driven at one-twelfth engine speed by a spiral gear off the mainshaft supplied lubricant, with a centrifugal filter system located within the timing side crank flywheel. The 1⅛ in Amal Type 29 carburettor had a long curved inlet tract to the laydown cylinder, while sparks came from a Lucas Magdyno incorporating an MS1 magneto, driven by a train of gears hidden behind the
tall, narrow, right-side timing case.
The sturdy – and heavy – tubular steel duplex cradle frame on the Sloper models was also used on the Square Four, and featured a double top rail and steel forgings for the bottom engine cradle, with further mounting lugs for potential sidecar attachment. The forked front downtubes were braced by a horizontal tube mounted a few inches below their junction with the steering head. The triangular engine plates were welded in unit with another horizontal cross-member connecting the bottom ends of these front down tubes.
The Webb-type girder fork was Ariel’s own design, with a single compression spring. Wheelbase was 56in and seat height a much reduced 26½in, taking full advantage of the low-slung motor’s architecture. Likewise, the 2½-gallon fuel tank, being lower than on other models, had special raised knee grips attached to its flanks. At the front of the tank top was a raised instrument panel incorporating the fuel filler cap on the left
matched by the Smith’s speedo on the right, driven off the gearbox via a cable passing through the rear of the petrol tank, with a clock at the top of the panel, and an oil pressure gauge at the bottom. Because the four-valve SG31 used higher revs than its two-valve counterpart, it was apparently fitted with slightly lower gear ratios. It appears that no weight for the complete bike was ever officially published, but it seems that 390lb dry is a reasonable estimate.
Production of the new models began in January 1931, with a total of 2880 Slopers of all types finding customers all over the world in that debut calendar year,
571 of them being the most costly SG31 four-valver. Under Jack Sangster’s shrewd management, Ariel had developed an extremely successful export division, resulting in approximately two-thirds of the Slopers built being sold abroad. These included 24 examples that year to Ireland, already a foreign country for the previous decade since the Irish Free State was created as a self-governing Dominion in December 1922. Eight of these were the top of the line SG31 four-valve versions, and more of these were sold to Italy (always a popular Ariel export market), Bulgaria, Germany, the Netherlands, France, and even Vietnam, then a French colony where two such SG31 models ended up.
In 1932 a further 1157 Slopers were built and sold up until September that year, when Ariel’s Carbodies Ltd parent company, into which Components Ltd. had been folded, went bankrupt, mainly thanks to the insolvency of its Swift car division managed by Carbodies MD / CEO Charles Sangster, Jack’s father.
Things briefly looked bleak for Ariel, but Sangster Junior was convinced of the firm’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. The Sloper singles did not survive the cull – though, perhaps surprisingly, given the austerity of the times, the costly range-topping Square Four remained in production, despite early examples frequently suffering from blown head gaskets, due to insufficient cooling of the rear part of the cylinder head.
This means that just 4037 examples of the Ariel Sloper were built altogether in just over 18 months of production, approximately 800 of them being the costliest and bestperforming SG31. Inevitably, this means that it’s the rarest such model today, with just 31 known survivors dotted around the world.
One of these may frequently be seen standing in the forecourt of the Sammy Miller Museum on England’s South Coast – but this time it’s not one of Mr. Miller’s 400-plus exhibits, but the ride-to-work transportation belonging to his part-time restoration assistant, Jim Devereux. Jim, 59, is a self-employed motor engineer with a fine collection of Ariels totalling 16 in all, from a 1924 500cc Tourer with a White and Poppe motor, to a genuine matching numbers HT-5 trials bike, like the one his employer won so many trials with in the 1950s and ’60s.
Jim’s Sloper was in a very different state to its current immaculate condition when he purchased it from a Southern Irish-based vendor at the 1989 Kempton Autojumble, then spent the next 20 years sourcing the parts needed to make it restorable. ‘It was one of the first of the 24 bikes dispatched to Ireland in 1931, to Ariel’s agents Lindsay & Sons of Dublin,’ says Jim.
‘The condition I bought it in was very poor, although somebody at one stage had sandblasted the whole thing, and sprayed it with red oxide primer, which probably acted as a preservative! The top end of the engine was missing, as were most of the original rear mudguard and stays – somebody had grafted on the remains of a Royal Enfield mudguard instead. But most of the tricky bits to get today were there, like the cast aluminium primary case, which is just gold dust to find.’
Without the top half of the motor Jim Devereux had no idea whether he’d purchased a two-valve or four-valve Sloper model, but fortunately the Ariel factory despatch records have been preserved, which show that Model SG31 bearing chassis no. S1433 and engine no. S1335 (there’s an imbalance because the same frame was used for the Square Four, remember) was shipped to Dublin on February 7, 1931. OK, but now he was on the lookout for a four-valve top end, scarcely the most plentiful of period Ariel parts.
‘Friends in the Ariel community just put the word around that I needed a cylinder, a cylinder head and all the rocker gear, and eventually, not by using the internet, but just by phone calls and speaking to people over a 20-year period, I accumulated the parts that were missing,’ says Jim.
‘An elderly gentleman local to me who’s a genius sheet metal worker made a new valanced front mudguard for it, because I had the remains of the original, but it was beyond restoration, so it got used as a pattern. Luckily the fuel tank was salvageable, because again, you just never see them, and I made a lot of other parts that were missing myself. Finally I could begin to start work on restoring it, and I completed doing so in 2013, just in time to go on display at that year’s Bristol Classic Show, 24 years after I’d bought it!’
But Jim Devereux’s 1931 Ariel SG31 is far from being a show-boating trailer queen, and it was only after thousands of miles of regular use that it won top honours as Best in Show at the 2020 Bristol Motorcycle Show at Shepton Mallet on the first weekend of February, just as Covid struck Britain. Before that, it had come away with the Best Overall award in major events like the Sunbeam Club’s annual Graham Walker Run in the New Forest.
Once lockdown started to ease later last year I could take advantage of Jim’s kind offer to let me ride a bike I’ll admit I hadn’t heard of before I saw it for the first time parked outside the Miller Museum’s workshop door with 5985 miles on the Smith’s speedo since restoration ended. An Ariel Sloper? Never! But yes, and now I could ride one…
Fitted with 19-inch wheels with chromed rims (standard on the SG31, but optional on other Ariel singles) wearing 3.50-section Barum tyres, the low slung Devereux Sloper’s 26.5-inch seat height makes it an extremely easy bike to sling a leg over, to ensconce yourself on the broad, well-sprung Lycett seat, which Jim has fitted with a comfortable soft leather cover. Despite the low seat the riding position isn’t cramped, with the footrests quite low and slightly rear set for extra room. The Sloper engine can be tricky to fire up from cold via the right-side kickstart, but after Jim showed me how to do it I found it easier when warm – apparently Ariel recognised that some owners had trouble with this because of the downdraught carb intake, hence the flange-mounted curved die-cast aluminium
induction tract on the OHV Slopers.
Once fired up the Sloper motor settles to a quiet, lazy idle. The amount of mechanical noise is really minimal, either because of the inherent design and reduced clearances, or Jim Devereux’s careful assembly – or both! There are no undue rattles or shakes, and engine vibration on the move is really negligible – this engine is a delight to use. Despite the extra potential for higher revs from the four-valve design, it’s still very torquey, which coupled with the extremely well set up hand gearchange – I never thought I’d ever write those words! – makes riding the Ariel a pleasure, not a chore. That’s not to say it’s a fast change – rush things, and you’ll miss a gear, or hit a false neutral. But with the pretty low first gear at the bottom of the gate on the right of the fuel tank, neutral easy to find when you want it and not unduly available when you don’t, and the evenly spaced top three ratios allowing you to make the most of the lusty engine’s enticing acceleration as you pull the hand lever upwards for higher gears, this is a vintage bike with modern manners.
You can even use the gearbox for engine braking, modern-style, because the way Jim has it set up, it takes very little movement of the lever to swap ratios, and each gearchange is precise and clean. I really enjoyed using it – again, words
I never thought I’d write about a hand-shifter!
Using engine braking isn’t an absolute necessity because the seven-inch SLS drums fitted front and rear to the Sloper are no good, because in fact they stop what is certainly a heavy piece of metal pretty well. The right-foot rear brake pedal next to the timing case is in fact pretty fierce – it’s very much either on or off, but it will stop you well from reasonably high speed. I had the Ariel loping along at 50-60mph very happily, with a great long-legged feel to it. It would have been a handsome long distance mile-eater in its day.
The Ariel Sloper’s good mechanical manners are matched by its handling, with the low cee of gee occasioned by the steeply raked cylinder an undoubted key factor in the ease with which it steers. After spending a good part of my 25 years in road
The Sammy Miller Museum in New Milton, Hampshire, UK is crammed full of interesting machines – including one of the biggest collections of exotic racing bikes in the world, and all are runners! These include the V8 Moto Guzzi, AJS Porcupine, Mondial 250 with dustbin fairing, Nortons, Ducatis, Suzukis, Hondas, Velocettes and many more! The Road Bike Hall includes a huge collection of factory prototypes and exotic designs from all over the world, and of course there are plenty of dirtbikes and trials icons, too – over 400 bikes in total.
The Museum is open to visitors daily from 10am every day.
Contact: Sammy Miller Museum, Bashley, New Milton, Hampshire B25 5SZ, U.K.
For further information and details tel. 01425 620777 or 616644 or visit www. sammymiller.co.uk racing aboard motorcycles with comparable architecture, like an Aermacchi classic racer or a modern Ducati Supermono, each with near horizontal cylinders, I know only too well what a key factor this is in endowing such a motorcycle with nimble handling, coupled with high speed stability and, above all, the ability to ride bumps well.
Though the Ariel Sloper’s rigid frame with its Webb-type girder fork doesn’t deliver the same suspension benefits as an Öhlinsequipped modern racer, it’s easier to shake off the effects of hitting a bump when leaned over in a turn on a bike like the Sloper with its low-slung motor than it would be with a more conventional vintage bike with a vertical cylinder, and that’s the way it turned out. Indeed, I found the Ariel-made girder fork ate up the bumps better than most other comparable period front suspensions I’ve sampled. This would have been an ideal ride along winding country roads – as most of them were – in 1930s Britain, with the glorious klaxon horn Jim has fitted alongside the imposing Lucas King of the Road headlamp to clear yourself a way.
Indeed, Jim Devereux’s Ariel Sloper is a wonderful example of a bygone breed of bike, which finds itself to be in fine fettle as it celebrates its 90th birthday this year. This is a lovely practical vintage motorcycle, which Jim deserves great credit for restoring so well – and then using regularly. It’s a living testament to the truth of the old slogan: Ride ’em, Don’t Hide ’em!