Ariel Square Four

This article was first published in Real Classic Magazine, and has appeared the the AOMCC Magazine, Cheval de Fer

Square Four History

If you are interested in engineering and engines in particular, go and look up square four engines in Wikipedia. The arrangement is called U configuration engine, or a tandem twin. Suzuki made a 2 stroke water-cooled version for their RG500, the close angle V Four Matchless Silver Hawk was cheaper and lighter (contemporary with the Ariel, similar, but only one crankshaft) and Bugatti built a 16 cylinder engine as two coupled ‘straight 8s’ but the arrangement is rare in the motorcycle world. There is a reason for that, but this is a story of people & their ideas, events & opportunities…

When Jack Sangster was demobbed from the Royal Warwickshire Regiment in 1918, he joined ‘Components Ltd.’, a supplier to the bicycle, motorcycle & car industry and which owned Ariel Works Ltd., a company based in Selly Oak, Birmingham. Components Ltd was run by Jack’s father Charles Sangster and whilst there Jack designed a lightweight car powered by an air-cooled flat twin engine. It caught the attention of the Rover Company, who set up a factory to build the ‘Rover Eight’ and gave Jack a job as Assistant Works Manager. He was 23 years old. In a post war cash-strapped market, the cars were to prove popular and by 1922 Rover were selling 125 cars per week.

Jack returned to Components Ltd in 1923 and joined as assistant Managing Director to look after production of the Ariel Nine & Ariel Ten motor cars. Ariel was engaged in the manufacture of a successful range of single cylinder motorcycles designed by Valentine Page, who had moved to Ariel from JAP in 1925, and its fortunes were on the up after a difficult period in the early ‘20’s. These machines had been designed to be cheap & easy to manufacture, and they were to prove so successful that 1927 sales were up 10-fold on 1925 sales, and in turn profits in 1927 exceeded the figures for 1926 by 500%; In October 1929 Jack, now Joint Managing Director was able to announce that over 19,000 Ariel machines had been produced that year, to the end of August – almost 550 machines per week. We can perhaps sense that Sangster’s team, on a roll and with a full wallet, were looking for a flagship machine.

In 1925 Edward Turner, renowned of this industry was located in Peckham, London and was running a motorcycle shop. History and folk lore tells us of his reputation as an ambitious man and not content with running his shop he campaigned an OHC single cylinder engine of his own design in the London-Exeter trial. He also had a design for a compact four cylinder engine with its cylinders arranged as two parallel twins, arranged in a square and with a chain driven overhead camshaft.

Edward hadn’t had much success showing his ohc single design to the motorcycle industry despite some initial interest from BSA. But it was at a meeting with Vic Mole, Ariel’s Sales Manager that he brought out his ohc four design and this aroused interest. A second meeting was arranged and he was driven from his home by an Ariel director to meet Val Page & Jack Sangster, and it impressed Sangster enough for Edward to be given his chance.

In November 1928 Edward Turner was offered a job at Ariel, working as a designer under Val Page, and was given an assistant by the name of Bert Hopwood. After 18 months this tiny design team had produced their engine, which was of unit construction with an integral 3 speed gearbox. Each crankshaft had a helical gear cut on the central flywheel which coupled the crankshafts and drove the gearbox. The engine, with a 51 mm x 61 mm bore and stroke was compact enough to go in a 250 single frame due to the overhanging roller big ends which considerably reduced width by avoiding the use of main bearings outside the cylinders. The crankshafts were short and stiff, reducing the rocking couple and making the engine smoother than an inline four. The lubrication system was dry sump, with oil in a compartment behind the engine, I am not sure this is true for the prototype engine, given the drive to the gearbox from the central coupling gear, but photos of the prototype engine and few and far between and the engine had a chain drive magneto with a distributor on the end of the camshaft

This innovative engine was going to be expensive to produce, and Jack was showing the signs of the hugely successful businessman he was to become and, having experienced difficult times in his father’s business was not going to spend money frivolously. For production, the unit engine was changed to use a separate Burman hand change gearbox. The helical gear teeth on the flywheels were replaced with straight cut teeth after engine #200, which were cheaper to machine and would have avoided the need to deal with side thrust. These were contained in a central oil fed compartment, which allowed oil to overflow into troughs under the big ends, and these in turn were lubricated by fingers cast on the connecting rods dipping into the troughs to splash the oil around. The drive to the gearbox was changed – the near side rear crankshaft was extended outward to provide a shaft with sprocket to drive the clutch. The engine was larger and heavier but was still compact enough to fit in the 500 sloper single frame, whose splayed down tubes fitted the Square’s crankcases. The handsome 500cc machine was launched at the London Motorcycle Show in 1930, with the Silver Hawk on the Matchless stand.

The press loved it. It would pull from 7 to 75 mph in top gear, a performance which was to be a feature of the Square Four experience for evermore, and the lightweight crankshaft allowed the engine to rev & promise great performance that included placing ‘Gaffer’ Littledale first in the London to Land’s End Trial that year.

The engine had its cylinders spaced at a 4 ½” pitch to aid cooling, but the size of the front mudguard meant there was a low-pressure area behind the mudguard, and hence very little differential air pressure to force air from the front of the block to the low-pressure area behind the block. A reputation for overheating began. As designed, the cylinder head was intended to function as a single item and so was held to the cylinder by eight bolts around the edge. Unfortunately, the temperature differences between the hot central area between the cylinders and the cooler area around their edges led to the cylinder head tending to warp upwards in the centre. The original cylinder head gasket, a one piece item, encouraged this. The Works solution was to cut up the head gasket and fit only the four bits around the actual cylinders. As Service Bulletin 40 from 1932 shows, this meant that only two bolts then acted for each cylinder head gasket, a far from satisfactory arrangement with the rudimentary gaskets of the day.

Another issue with the OHC fours was the problem of them not getting hot enough in the winter. This lead to condensation forming in quantity within the cam chain cover which then found its way into the engine oil. Since oil floats on water and the oil pump intake is from the bottom of the oil reservoir, engine damage follows.

Development woes aside, the machine was a revelation to journalists used to the typical single cylinder machines of the day. Production of the 500cc four machines began in earnest in February 1931.

A feature of four cylinder machines is that as the inlet valve on a cylinder starting its inlet stroke starts to open, the inlet valve on the cylinder starting its power stroke starts to close; thus the inertia of the incoming charge, which tends to ram mixture into the cylinder beyond atmospheric pressure, is lost to the first cylinder, the first cylinder sucks gas from the second cylinder and cylinder filling is reduced as a result – the answer is to fit several carburetters & separate the inlet tracts. The Square Four was of course provided with a single carburettor and the common inlet manifold prevents use of this ram effect; furthermore, the cruciform manifold design restricted performance by its poor air flow. Examination of the inlet tract reveals a flow path as smooth as the casting process left it, with no access for grinding tools, coupled with right-angle bends and shrouded, vertical valves.

The machine was to prove popular with sidecarrists, and to offer more power it was enlarged for the 1932 season, which began in October 1931, at the same price to 601 cc by increasing the bore to 56 mm. This reduced stress on the engine for owners using the performance. At the same time the cylinder head was redesigned and there were now eight head bolts. The 600 cc machine, called the 4F/6.32 was ridden by Ben Bickell in an attempt on the Maudes trophy at Brooklands in 1932. The bike was fitted with a supercharger to improve performance and achieved several good results, notably covering 700 miles in 700 minutes. Bickell failed to achieve his aim though, which was to be the first to cover 100 miles in one hour due mainly, and unsurprisingly with a blower fitted, to head gasket issues.

Ariel Works, 1932 - Courtesy Jerry Mortimore
By 1932 the world was in the grip of the Great Depression and in September Components Ltd were forced to call in the receivers. Jack was by now a wealthy man and seeing that elements of the business could be profitable he bought the Ariel name and some of the machine tools from the receivers and set up a new business in the old Ariel ‘Fleet’ car manufacturing works, which he owned personally. The concern became Ariel Motors (JS) Ltd. With the liquidation of Components Ltd., Val Page moved to Triumph, from where he gave us the 6/1 twin in 1933, leaving Edward Turner at Ariel as Technical Director. Turner was 31, and Bert Hopwood was his Chief Designer.

For 1934, costs drove a program to standardise the range around one frame, that of the 500 single, for all models. This necessitated a redesign of the crankcases for the Four and the lubrication system was improved at the same time, becoming ‘wet sump’. This design resulted in a much shorter engine than the previous long case arrangement.

Late in 1935 Jack Sangster bought the motorcycle business from the Triumph Motor Company for £50,000, leaving Triumph to pursue their car manufacturing, eventually to be absorbed by the Standard Motor Company in 1939. Edward Turner was appointed General Manager at the Triumph Engineering Company and Bert Hopwood followed him in 1936. Val Page moved to BSA as Chief Designer, where he was to design the famous M series machines; his role at Ariel was taken by Frank Anstey, who had joined Triumph from Rudge, and who transferred to Ariel Motors as Chief Designer to start work on the lubrication system for the Square Four.

The engine for the Square Four was completely redesigned for 1937 with a simpler overhead valve configuration, with a single camshaft operating the valves through conventional pushrods & rockers and the engine was generally enlarged. It had a 995 cc capacity with a 65 mm bore x 75 mm stroke, with a 5.8:1 compression ratio and was called the 4G; it provided 38 bhp and 100 mph. The OHC engine had lacked flywheel effect and this was corrected for the 4G by moving the coupling gears outboard and adding flywheels and bob weights to the crankshaft. The flywheels were staggered and overlapped to keep the engine as short as possible. Making the engine wider and keeping the overhung big ends would have meant excessive bending moments in the crankshafts, so the new engine got conventional white metal bushes on the timing side and roller bearings on the drive side. Forged crankshafts meant split big ends with white metal bearings. The crank cases were redesigned too – the OHC four’s cases were horizontally split and had a separate carrier for the main bearings; the new design had vertically split cases which reduced machining costs considerably; it had an iron head and barrel with a separate alloy rocker housing and inlet tract and separate iron exhaust manifolds. There were now twelve cylinder head bolts, improving pressure retention and gasket life. The cylinder spacing had changed and the engine was now a rectangular four - only the OHC engines were true Square Fours.

An engine of this design was always going to to get hot, so the new arrangement was more spread out with more space between cylinders to assist cooling. The new design had a single central camshaft between the crankshafts, driven by chain from a crankshaft sprocket; the chain drove a Lucas magdyno behind the cylinder block and was tensioned with a Weller blade tensioner. The camshaft was relatively long and was stiffened in the centre to counter the prospect of any camshaft whip - there was said to be a problem when tuned motors were run at excessive rpm for sidecar racing, or for sprinting. The plunger oil pump was driven directly from the camshaft sprocket and drew oil through a strainer in the sump and passed it back to a separate oil tank. Oil was delivered from the pump to the rear crankshaft bearing, then to the front crankshaft bearing, then through an external line to the rocker box, to drain down the pushrod tunnels, over the camshaft and into the sump.

Issues were to emerge with the new engine layout relating to the connecting rods. The nearside connecting rods were fed using long 3/16” galleries through the crankshafts, fed from the offside main bearing. Unlike the twins and singles, the sludge traps in the SQ4 cranks shafts are very small and build up of sludge leads to blocked oil ways to the offside big ends, leading to connecting rod failure – not a pretty sight. The nearside rods are said to fare the worst, since they are furthest from the oil pump – experience tells us that these sludge traps are the first to block...

Woe betide the new owner who runs his engine without personal knowledge of the state of these traps.

Anstey introduced a spring frame version for 1939, with girder forks at the front and the tapered handlebars. It cost an additional £10 on price of rigid models, and offered a softer rear end with constant chain tension thanks to a pair of links that allowed the plunger-sprung rear wheel to move in an arc that matched the radius described by the chain. A clever lesson in geometry, discussed at length in Cheval de Fer, it had several bushes on each side that would wear rapidly if not kept religiously greased leading to wallowing at the rear.

Ariel produced a 599 cc version of the Four for 1939, called the 4F, alongside the ‘deluxe’ 1000 cc 4G and the ‘standard’ 1000 cc 4H. Where the 4G had fishtail silencers, chromed & lined rims, a QD rear wheel and a 3 7/8 gallon tank, the 4F and 4H shared cycle parts with plain silencers, painted rims, no QD rear wheel and a 3 ¼ gallon tank. The 4F & 4H models had a 20” front rim and a 3.25 section rear tyre; the 4G had a 19” front rim and a 4.00 section rear tyre.

Anstey left to take up a post at Villiers in April 1939, to be succeeded as Chief Designer by Val Page who returned to Ariel in May to develop the W/NG from the 1938 competition model.

Page designed the damped telescopic forks and a twin cylinder engine during the war. The fork design was simple & effective & would serve Ariel & BSA through to the 1950’s on A, B & M series twins & singles, though the fork did not appear on production bikes until late in the 1946 season, and then only on Square Four and Red Hunter machines. The twin engine went on to be used in the KG and KH models which were produced from 1948 until 1957.

Towards the end of hostilities, it was becoming clear that the availability and price of raw materials, the new purchase tax and the state of the economy were going to depress the market and as a result Jack Sangster decided to sell the Ariel business to the BSA Group, to concentrate on Triumph. The deal went through in December 1944 – the Ariel workforce promptly went on strike, until it was confirmed that Ariel would stay at Selly Oak. BSA also acquired Sunbeam from AMC at this time. Jack remained a director at Ariel, and the deal included an option for BSA to purchase Triumph should Sangster wish to sell it. This eventually happened in 1951, a deal worth £2.5m which included a seat on the BSA board, and resulted in one of the world’s largest motorcycle manufacturing groups marketing similar machines from different factories, all competing against each other; the ingredients for a disastrous bake-off were assembled.

After the war, the 4G became available again in 1945, but the 600 cc 4F version and the 1000 cc 4H were gone. The iron engine 4G got new connecting rods with shell bearings in 1947, but Val Page was looking at more extensive modifications to the Square Four engine with draughtsman Harold Hill. Prototypes were ready early in 1948. Development problems with stripped spark plug threads lead to the adoption of bronze inserts, and the selection of poor quality alloy by the procurement department meant the head stud design was changed twice following persistent head gasket problems. This would have been exacerbated by the fact that access to the twenty head bolts was poor. Considering that the alloy head would have better heat conductivity than the previous iron head, they reverted to integral exhaust manifolds. The team initially looked at reworking the Square as a Vee four to improve cooling, but of course this would mean an extensive rework of the crankcases, barrels and frame and was not pursued. The block did receive some attention however and was also changed to an alloy casting, with iron liners. The casting featured a ramp, formed in the area in the centre of the cylinders and designed to direct incoming air up into the cylinder head.
Mk1 Engine
The alloy engine yielded a weight saving of 33 lb. We’ll probably never know what initiated the move to an alloy top end, but it’s interesting to note that after WW2 aluminium was more cheaply available than steel and that a world famous aluminium bodied 4x4 made its debut at the 1948 Motor Show

Mk1 Square Four
The new bike was tested to 92 mph by Motor Cycling in 1949. I don't intend to repeat that performance!

The new engine was provided with coil ignition, which was more reliable in heat & cheaper than 4F's magneto. A larger battery was fitted for the 1951 season, no doubt to extend the period that the bike could be driven at low speed without exhausting the battery.

The Square Four, and other Ariel models built for the 1951 season were victim to one of the consequences of the Korean War – that the Nickel suppliers, considering the need for materials for military uses, withheld nickel from the open market. This mean that the tanks were no longer offered with chrome plating & painted panels, but with solid Damask Red or black paintwork with gold lining.
The MkII Engine

The heating issues persisted, necessitating further design changes which led to the four pipe version offered for 1953. It had separate alloy inlet and exhaust manifolds which allowed more to flow around the valves by giving an increased cooling surface and it had a gear type oil pump. The Mk2 offered 42 bhp, which equates to 0.091 bhp/lb, the best yet. The new engine had a duplex timing chain and revised gearing, allowing the dynamo to run at a higher speed.

The 2 pipe version was now christened the Mk1 and although nominally still available for the 1953 season, ceased production in December 1952. The MKII took over from January 1953 with minimal overlap between the two. This year end change was unusual for Ariel who usually changed models at the beginning of September or October, in time for the autumn motorcycle shows.

Earles Fork Ariels, courtesy Gary Jolly
During 1953, Ariel were engaged in the development of a Mk111 Square Four with Earle’s leading link forks dubbed the ‘Royal Hunter’, whose development must have gone on to an advanced level since a description of the fork appears in the sales literature and the Owner’s Guide. The forks, with a new twin leading shoe front brake, were applied to the KH twin and VH single as well. It was never produced, supposedly because the Earle’s forks fitted to Les Graham’s MV contributed to his fatal accident in the 1953 Senior TT. Ken Whistance, Ariel’s new General Manager, instructed Val Page to drop the design and pursue a swinging arm frame for the whole range instead.

1954 brought a change away from the Solex carburetter, to a small SU which needed changes to the frame to clear its dashpot. In the same year, the oil tank volume was increased marginally, but it also had a very different shape which increased its surface area significantly in an attempt to cool the oil. The tool box moved to the nearside to allow space for the new oil tank.
Last of the Line - MkII Square Four
During its 23 years, the Square Four had grown from a sprightly 330 lb (the 600 cc ohc) to a rather more portly 460lb (Mk2) via the middle-aged Mk1 at 435 lb. The 600 cc OHC model gave 24 bhp at 6000 rpm, making a power to weight ratio of 0.072 bhp/lb; the iron 4G, which weighed in at 476 lb, gave a power to weight ratio of 0.073 bhp/lb while the 35 bhp Mk1 gave 0.08 bhp/lb., which doesn't sound much but is a 10% difference, in the right direction. The 40 bhp Mk2 gave a power to weight ratio of 0.087 bhp/lb

Val Page was still continuing to produce new designs towards the very end of the 1950’s, notably the 350 cc ohv Leader twin and the 700 cc Leader Four. This was an in-line four, an original engine design coupled to a commercially-available gearbox in a Leader style machine. The engine was intended to fulfil potential military contracts for generators sets, rather as Triumph’s GP engine had done 15 years earlier but the contract was cancelled. It’s perhaps safe to assume that this reduction in production volume was sufficient to cancel the project.

Reproduction swinging arm Square Four

A further development, for the 1960 model year was the application of the proven swinging arm frame to the Square Four. Two prototypes were produced of this MkIV and there was also an experimental model with trailing link front forks designed in a similar style to those used on the contemporary prototype Leader 4.

1959 was to prove an eventful year. Edward Turner (who was by now in charge of the motorcycle business of the whole BSA group) stopped all development at Ariel. Val Page retired in January 1959, at the age of 67 and earlier than he had intended, after one of the most illustrious engineering careers in the British motorcycle industry. He was succeeded by his deputy, Bernard Knight. We can guess that he may have been discouraged by the cancellation of the 350 cc ohv twin and the 700 cc Inline Four projects.

The end came in April, when the last 3 Mk 11s were despatched from the Selly Oak works on April 30th. All the other four stroke Ariel’s were discontinued, to allow the company to concentrate on continuing the success of the two-stroke Leader and to trim out competing models from the group’s catalogue (the BSA A10 & Ariel Huntmaster, for example) & thereby reduce group costs.

So finally, 1861 Square Fours had been built in the last 3 years. It still had inherent cooling issues & poor breathing to limit its performance, but it stands testament to the engineering innovation so beloved of the classic vehicle movement today. Its legacy is perhaps a technical blind alley, but without such machines our hobby would be considerably less varied and considerably less interesting.

In the beginning

Following the Square Four history I thought I’d share some of the trials, tribulations and triumphs of the three years I have spent dragging my own Mk1 Square Four from its early decimation in Essex and back to the roads of Norfolk.

I’d been looking around for a bike to buy for my 50th birthday, thinking mainly Velocette – intrigued by their reputation as an ‘engineer’s bike’. I’d started reading all the Velo articles I could find, re-read my old Haynes manual and scoured the internet for information. I’d even joined the VOC and bought all the books. Engineering has been a passion and a pastime since school – I’ve done over 25 years in the oil & gas industry now, designing equipment for deepwater environments. The niggle was, I’ve had a thing for Harley WLs for years, attracted by that ‘30’s ‘wasp waist’ look that you get from a plain rear mudguard and a single saddle, so a late Velo just didn’t cut it aesthetically. Shallow I know, but looks are important!

EBay is such a well-used auction site these days that the prices are going through the roof, unless someone has had the misfortune to put their Pride & Joy in the wrong category. Gumtree however is a different kettle of fish… Some searching around put me in touch with a very nice lady from the Essex VMCC who had 85% of an original-numbers 1951 Square Four in her shed. We made a deal, and said lady arrived one Saturday in October 2011, in a van with husband, two Norton 500Ts and a big pile of Square Four parts.

Amelia had arrived. I’m slightly amazed that I am writing this the day after I rode her for the first time, and almost three years after she arrived, but she has certainly kept me fully distracted for that time. Old bikes are uniquely and usefully diverting from the modern world, a welcome relief from the mundane repetitivety of the workplace and the emotional ups and downs of family life, especially so if they are a little different in their engineering and perhaps from a marque that you are not familiar with.

Finding, fixing, finishing

The Ariel would be my fourth bike restoration, after an AJS, Matchless and most recently a D1 Bantam, but the first one I would have built from a van load of parts. Most of the steel parts of the bike were already black, but it appeared to be very thin and rust was coming through so it would have to be done again. The thing was, at this point I wasn’t at all sure what fitted where and I had no mudguards, seat or battery carrier. Other more expensive things were missing too – like the speedometer; the proper oil pressure gauge and the red-spot ammeter were missing too. Red-spots are the PA speedos of the ammeter world and cost an arm and a leg. I decided, inspired by an article in another bike magazine where a professional had restored two SQ4s, initially building them in bare metal to assemble the bike, register and ride it before I did any finishing work. That way I could rework any parts I messed up during fitting without worrying about having to redo the paint or plating. That worked up to a rather embarrassing point, but you will have to wait until the later in the story for that...

Getting started

I made a list of all the parts that I would need, or that needed attention, adding suppliers, prices, part numbers and descriptions. This was partly to keep track of all the bits, but also was useful in proving to my dear wife that I knew exactly what I was spending each time an ‘un-birthday’ present dropped through the letter box, usually bearing the giveaway Draganfly logo on the packet, and how at any point in time I knew what the total spend was, what the forecast spend was, and how much the bike would be worth at the end. This had proved very useful with the Bantam – even though she always tells me that my labour rates are unreasonable at £0.00 per hour.

So I started working through all the boxes of parts, cataloguing and restoring as I went, starting with easy things like the ignition coil, switch, distributor and lights while I read everything I could find on Square Fours and Ariel’s in general. There were some quite significant other bits missing too – there were no mudguards or rear stand, though I had all the stays, the chainguard, both tanks and the diminutive side stand.

I started documenting the rebuild through a blog, though I guess if you are reading this you probably know that already...

Speedo, Ammeter & oil gauge

One or two of the parts that are typically missing from old bike projects and basket cases in particular are the instruments. Intricate and expensive they were often the parts that were first sold as spares or robbed when the machine was laid up, and today that intricacy often results in an expensive professional repair that exacerbates their reputation as expensive items to have in your list of missing parts. You can spend £1500 on a Smiths PA speedometer these days – more than my Bantam is worth as a running, restored machine.

Mk1 Square Fours use the more recent, common and cheaper chronometric speedometer: fortunate, since mine was missing…

My understanding wife had, at some point in the past, bought me a £5 wrist watch from eBay – broken of course – thinking I’d enjoy tinkering with it. This blossomed into a bit of a hobby – the £5 wrist watch grew into a small collection of Omegas, bought broken, fixed & sold or consigned to the jewellery box – so the chance to get inside a Smiths Chronometric was an in interesting challenge, if only to figure out how it worked. The Bantam’s D shaped speedo was the first to suffer the treatment, and is still working fine years later. Like most watches all they often need is a clean and the spiders chasing out; this one had a main drive pinion that was ground to dust and had to be replaced with a spare, but with a freshly painted case it’s almost as good as new.

The oil pressure gauge was a lucky find in almost-as-new condition…

But chicken dentures come in other forms too. One or two coil ignition bikes used the white faced Lucas ‘Red Spot’ ammeter, which is little more than an ordinary Lucas ammeter with an MES bulb holder attached to it.

Mine, like all the expensive bits in all my projects (or so it seems) was missing. eBay came to the rescue with a bedraggled looking ammeter which had once been a red-spot type, but aside from the white face with the window was in a terrible state. At least it was cheap.

I stripped it down and repaired the cracked case, replacing the bezel with a better example. Internet research should me what the bulb mounting arrangement should look like.

So, armed with some Tufnol, a piercing saw and a pencil I made a new lamp mounting, using some brass sheet to mount the lamp holder just as Lucas had intended. Finishing off with some knurled 2 BA thumb nuts, it looks the part and works perfectly.


The front and rear mudguards came from eBay along with a lower chain guard. To say they were moth eaten is an understatement, but at least the local welding supplies shop got some business. I put a lot of sheet metal into the rear one particularly, which had clearly had a pillion seat at one time and was full of holes and almost in four pieces – there was a lot of fatigue cracking as well.

The front mudguard came with a nice little brass badge indicating that the bike they belonged to had been supplied to Hallet’s of Canterbury. Writing this in my blog, I was contacted by Marcel Hallet who kindly gave me some lovely scanned copies of the shop in its heyday, complete with Ariels on display. It’s amazing who you come across.

I spent many hours in the workshop beating steel sheet into curved shapes to repair the mudguards, and welding them in place until they were stronger than they had ever been. I had a similar experience with the oil tank, which while not rusty had an enormous dent on the panel behind the battery box – the consensus of the AOMCC forum was that the battery must have exploded… a little joke. Anyhow, I attached various steel rods to the centre of the dent in an attempt to pull it out, only to create a Grand Canyon of cracks – I did what I should have done at the beginning and cut the dent out replacing the gap with a fresh piece of sheet, MIG’d into place. Three pressure tests and three re-welding sessions had it water tight.

Gearbox alignment

I was a bit concerned by the gearbox, whose number G107J51 denoted that it belonged to a KH from 1951. This was a worry, since I had learned from my research that due to the extra width of the coupling gears the Square Four engine was offset to the right and the primary drive to the left to accommodate the 4.00-18 rear tyre. This means that the gearbox mainshaft is longer and the gearbox case is different, to put the gearbox sprocket in the right place and all this was confirmed by looking at parts list for Square fours and KHs of the period, fortunately available from the AOMCC archive. This is the danger of buying bikes in bits, and it wasn’t the last KH part I didn’t know I’d bought either…

All I could do at this stage was put the rear wheel in the frame and try and convince myself the gearbox sprocket was correctly aligned…

Carb, plating and the dynamo

The Mk1 uses a Solex 26AHD carburettor, which has multiple jets and a butterfly throttle valve and which was used in pre-war Peugeot and Citro├źn cars. Conventional wisdom suggests that the constant suction from the multi-cylinder engine causes conventional throttle slides to stick open, and since the OHC Square Four used a slide-type carburettor maybe this had been a problem in earlier years. It’s unlikely that Ariel would have chosen the Solex unless they had to, since, according to the spare parts books a spare Solex 26AHD cost £6. 10s in 1951, while a spare Amal Monobloc cost only £4 7s some 7 years later.

My carburettor was all present and correct in the tea chests Amelia had arrived in but as usual was covered in primordial ooze. My current favourite carburettor cleaner is a kitchen/bathroom descaler (not to be used on aluminium, says the label, in an inviting fashion) which cleans off old fuel and alloy oxides beautifully. The steel parts were originally cadmium plated, and have been re-plated with bright zinc.

The Bi-starter knob and the air bell, both unnecessary for shaking down, will be added later.

For the Mk1, Ariel chose to change the iron 4G’s Lucas magneto to coil ignition, probably because they don’t respond to the heat well in their sheltered position behind the block. For this they needed a larger dynamo to cope with the load and eventually fitted a larger battery as well: Lucas offered the C35SD dynamo with on-board distributor, also used on the Royal Enfield twins apparently – it delivered 70 W at about 1700 rpm. It’s driven at engine speed. Stripping the dynamo was one of those ancillary jobs you do whilst working up to the real stuff – mine was full of oil from a failed seal. Happily the field coils and armature checked out ok and with a clean, paint, new bearings, seals and brushes it was good to go. The original Lucas regulator was stripped of its innards and provided with a V Reg 2A electronic controller running the charging system at 6V.

Engine Work

At some point I was going to have to start on the engine rebuild, though this got substantially delayed by the fact that my Bantam decided that it didn’t like its timing side mainshaft out in the North Norfolk countryside one day, so it got a second engine rebuild a couple of years after the first.

When the Bantam was back on the road, I returned my attention to the Ariel. I stripped & cleaned the engine and set to with the micrometers and bore gauges. The bores were +0.020” but hadn’t seen much service since, so they would just need a hone.

The block however had a fin missing and the head was worse – nothing mission-critical, but two rocker shafts with duff threads and about six damaged fins. Fairy Godmother came to the rescue though – in the form of a reconditioned head from Drags that appeared on eBay at just the right time. Clean, no fin damage, new valves, guides, all threads Heli-coiled and both top and bottom surfaces skimmed. Luvvly Jubbly!

I spent the next few weeks worrying about the gearbox until I could get the wheels, frame and forks together to look at the chain alignment. It wasn’t until April 2012 that I had bolted up the Anstey Link parts, built up the forks and mounted them and I was able to fit the wheels and move the bike around. While the bottom end was still together, I put it in the frame and built the primary case up. It appeared to line up with the clutch chain wheel. With a large piece of bar stock across the route the primary chain would one day take, I could see the chains would all align. It looked like I was out of the woods at last.

Encouraged by the alignment situation, I moved on to the bottom end strip.

This was pretty straightforward. There were no damaged threads in the cases or the coupling gear cover, though the outrigger bearing on the rear crankshaft was badly pitted. Its oil seal fell out in 7 pieces, held together only by its spring – and it had only seen 60 years’ service. Shocking! You have to use a special puller for the coupling gears which came from eBay, and following that I dismantled the timing side which revealed no horrors other than the fact that the dynamo sprocket had no retaining nut, and then we were ready to split the cases.

This didn’t reveal much drama either, apart from a mysterious chunk of cast iron, which I never did find a home for. Several days of cleaning and measuring followed. I prepared a chart showing all the wearable dimensions in the engine, with the manufacturers tolerances and the actual dimensions so that I could see what was worn out, what was likely to wear out soon and what was safe to leave.

With the bottom end apart, I learned that dire warnings about blocked sludge traps in those engines are to be heeded – number 3 big end oil way was almost closed off, a fact that was witnessed by the state of the big end shells on that cylinder. Not dreadful, but much worse than the others.

Blocked Sludge Trap
The big end and main bearing journals were OK though, but the camshaft bearings were not happy.

Looking around the magazines & the internet, I found Bernard Ashpole’s of Bishop’s Stortford advertising that they could repair white metal bearings and indeed whole engines. I called Bernard one day and he was confident he could help & so was I when I learned that coincidentally he was working on what turned out to be an OHC Square Four.

So one day on the way to work I carted most of the engine down to Ashpole’s. They replaced the mains & line bored the timing side bushes, and lightly ground the journals. They ground the camshaft journal as well, and made a new bush to suit.

A nice man with a TIG set built up a new fin on my barrel, and they honed the bores.

Wheels, paint & Aerographics tank paintwork

A big step in a bike rebuild, I think one of the major turning points is the wheel rebuild. Shiny rims and spokes, especially rims with painted centres are a focal point almost as significant as the tank. I like to retain my rims if I can, mostly because they have been with the bike since it was built and I don’t think I have the right to throw them away. So, with the engine away out came the camera, ruler and plywood wheel jig.

It’s vital to record wheel offsets and spoke patterns, and to get a sample of each of the original spokes. Half width hub bikes typically have four types – in the Ariel’s case two plain lengths on the front and two butted lengths on the rear, in a heavier gauge. Central Wheel provided their usual excellent service, with stainless spokes and plated brass nipples. I used plated steel nipples on the Bantam – 4 years on these are rusty. JD Wyatt Polishing did the plating, and I painted the hubs myself.

I was a little paranoid, probably needlessly, about matching the tank colour to the wheel centres. I went to Aerographics in Horsford, where John Spurgeon mixed the damask red paint to match a sample from the inside of one of the wheel rims, which had been hidden in the dark under a tyre for many years.

When the rims had been plated, John painted them and the tank in two-pack and together we agreed how the lining would fit around the rubbers and badges, using data from the Danish Ariel club website. The result was first class.

I built the wheels myself as usual, with Avon Speedmaster & SM Mk11 tyres.


Another job while the engine was away was to have a look inside the gearbox. The gearbox Ariel used on the SQ4 and the KH twins until 1952 is the Burman BA, which had been used on various Ariel machines since 1931.

Having established that the gearbox was the right one, I stripped it on the bench to clean and inspect it. I didn’t find anything untoward; it got new bearings a new sleeve gear oil seal, new gear indicator parts and a new inner case as the clutch cable boss was broken. This new case was missing its kickstart bump stop, so I had to make a new one. The case was also devoid of any marking, so that KH gearbox number is now consigned to the spares box.

Building up the bottom end

Getting the engine home again, I set about the cases, fins and barrel flange with the polishing machine. I needed a new tappet block from Drags, as one of them had come out in pieces and I needed to make sure everything was clean enough to go back together.

The pistons measured up OK, but needed a lot of carbon cleaning out of the grooves. The small end bushes were very tired and needed replacing; the big ends got new shells since they were on the edge of acceptability but the journals were in tolerance.

I polished the rods and replaced the big end nuts.

Ashpole’s had fitted the main and cam bearings so I built the bottom end on the bench after all the polishing was done, sealing with ThreeBond.

Once I had the bottom end together I could put the engine back in the bike. It was clear that I wouldn’t be able to lift it in complete and I’m not sure how you can get them in fully built but I know Ariel bench ran the engines before they went in the bikes.

So with the bottom end in and the gearbox built and fitted, I could fit the coupling gears, the primary case and the clutch and finally lay to rest the old bogey – the gearbox mainshaft length. I’d collected all the parts – good plates, new springs, screws & needle rollers and I had painted the clutch basket. In the end, all the worry was for nothing – it went together easily and the chains aligned perfectly.

So in theory I could set about the top end – but I had a problem. No piston rings were available from the usual sources in the sizes I needed, so I needed to get the measuring tools out again and find some. Three options came up – one involved machining the grooves to take thicker rings, which I wasn’t going to risk anytime soon; the other options were rings that would fit straight in from JP in Australia (thanks to an AOMCC contact again) and from FW Thornton in the UK. Delivered to my door, they would be about the same price. Duncan at Thornton’s had been very helpful, and they got the job.

It took quite a while to sort the rings out. I wanted to learn how they were specified and how the grooves were designed and with the help of Phil Irving’s ‘Tuning for speed’ I was able to come up with the ring dimensions I needed to fit my pistons and bores.

The only problem was that the stock levels of my chosen compression rings were pretty low and I would have to wait. I needed something else to do.

More tin bashing

A couple of things that were missing were the battery carrier and something to mount the coil on, and while I was waiting for rings I got on with these. I like making stuff, it’s the part of a rebuild that makes me feel I have contributed something, rather than bolting together a collection of parts.

Soon to become a battery carrier

The battery carrier was easy – sheet steel fabrication against drawings provided by the ever-helpful Brenton Roy of the AOMCC, and the stainless parts came from Acme Stainless in Lincoln, along with countless fasteners. Brenton has a 1951 Square Four and is based in Adelaide, South Australia. So, the intercontinental Ariel network operates through the excellent AOMCC forum, which is populated by a lot of clever people who are happy to help you from all corners of the world!

The coil mount was confusing – you see them mounted under the seat, but you also see original barn-find bikes where the HT lead disappears behind the battery. I looked at all the bikes I could find, especially the un-restored barn finds that appear occasionally. Sometimes you can see the top of a bracket appearing behind the battery as well –but there is nothing in the parts list, which probably means the original bracket was bought in from Lucas and not manufactured by Ariel at all. I came up with my own design, styled in the flavour of Ariel bracketry from the period based on shapes from the oil tank and battery brackets.

Battery & Coil Mounting
I guess that Mk1s, the first Square Fours with coil ignition had the coils initially mounted vertically behind the battery but that Ariel moved the coils to a horizontal position under the seat where it was less likely to accumulate rainwater in the HT connection.

Engine top end build

Getting the rings back meant I could start assembling the top end. I began by gapping all the rings on the bench, fitting them to their pistons and into their newly-honed bores to prove them before I tried to fit all four simultaneously with a heavy cylinder block teetering about in space.

I fitted the pistons in their original positions with my trusty old heat gun and gave them new circlips; then with the base gasket in place I compressed the rings using strips of tinplate and tie-wraps.

It took 6 hours over two days to get the block down. I'd get the block over all the compression rings, and it would persistently get stuck on cylinder number 1. After five attempts, which included checking ring radial thickness again, I realized that the 2nd ring on No. 1 had no shiny filed surface on the end - it was straight out of the box and had not been gapped at all.

That's what comes from working sporadically over several weeks. You need military precision on your record keeping, and to meticulously check & recheck what you did yesterday...

Once that was fixed, I was pleased to lubricate the bores with WD40 and to turn the engine over a few times.

Cylinder Head

So we were all set. The sun was shining, I had a day free (after cutting the grass and making the family dinner) and I had all the parts, including a very nice text from Bruce Longman via Draganfly with explicit instructions. I had some high temperature silicone gasket as recommended by Bruce. Loctite say this is suitable for operating temperatures up to 275 degrees C (sustained) with excursions to 300 C

I placed all the head nuts in position between the cylinder block fins, under their holes, with the flanges upward. Next, I manoeuvred the head under the frame tube and dropped it into place over the studs, making sure the extended, rounded ends of the studs dropped into the nuts. Adding the sleeve nuts inside the rocker boxes, and the 5/16" CEI reduced hex nuts outside the rocker boxes I was able to hand screw these down finger tight.

And as an AOMCC member from Holland pointed out in a comment to one of my blog posts, this would have been easier without the rockers! You cannot fit the pushrods with the rockers in place either (they don't slide sideways far enough) so I may as well have left them off... although I do like to trial fit everything at least once.

Very peculiar valve timing. #3 is correct; #1 exhaust is in someone else’s tappet…
Next, with my thinnest 5/16" CEI open spanner, I engaged all the nuts on the downward facing head studs and turned them as far as they would go without using and force. I realised now that if you leave one undone, and tighten the others, you will crack a fin by virtue of the loose nut pushing downward onto the fin below.

Once I had all the nuts finger tight I could see the head finally come down onto the gaskets. I continued going around all the nuts inside & outside the rocker boxes until they were all snugged down finger tight.

Push rods, oil pump and timing disc.

I spent two weeks setting up the valve timing on number one cylinder. I set up the timing correctly on the inlet valve, but when I went to check the exhaust valve it opened just after TDC on the power stroke… After messing about with chains and sprockets for ages, I checked number four cylinder and it was perfect. Since they all run off the same camshaft, I was flummoxed.

I had left the pushrods out of numbers two and three, to make the engine easier to turn over. I decided to put them all in, to check the other cylinders. Number three was all ok, but I could not get the pushrods in to the number two tappets.

More messing about went on, until the penny dropped. I had number 1 inlet pushrod in the number 1 inlet tappet, all well and good but number 1’s exhaust pushrod was in number 2’s tappet, crossing over in the pushrod tunnel!

Mighty Morgo
So in the end, two weeks of head scratching & stiffening knees later, the problem was easily fixed by the same idiot that caused it in the first place. We could now complete the fitting of the pushrods and rockers, and fit the Morgo oil pump.

The Morgo needs to be bled of air before you close the timing cover, since it is a gear type pump & due to running clearances between the pinions it will not pump air, so I had to complete the hookup of the lines before I could bleed the pump. This was tricky, because the rocker oil feed union was missing, out of stock everywhere and I didn’t know what it looked like. Clay at Acme Stainless to the rescue, who found one in a drawer and made some up in stainless – they are now available on his website.

Fuel tank

Another worry was my lovely shiny fuel tank. All the period & recent pictures of Square Four I had seen showed a balance pipe across the front of the tank and a single tap at the rear.

Mine had no balance pipe and two taps. One day, RC105 dropped through the letter box with a lovely 1952 KH on the front cover – with my tank on it. No balance pipe and two Ewarts petrol taps right behind the rocker boxes. Oh dear…

Still, it fits of course, and makes the bike usable and still looks lovely. It has only one tap now – I plugged the other one – so the capacity is a bit limited. I have an example of the correct tank as well, but it needs a kilo of MIG wire, some sealer and £250 worth of paint. That will be a job for retirement I think…

Finishing Off

Since I sorted that little mystery out, it has all been plain sailing pretty much. Finishing the wiring, making cables, hooking up the oil lines & commissioning the electrics… There comes a time when you realise that you are tinkering with stuff in an effort to delay some job that is worrying you, so one day I took the 850W power drill out to the shed and with oil in the tank and the plugs out I ‘span’ the engine over on the crankshaft nut… after I had almost burned the drill out getting it moving. When I had achieved the first few turns it eased up considerably and I was able to get pressure on the oil gauge and oil returning to the tank. Using the bleed port on the Morgo pump I was able to improve the situation still further. The timing cover finally went on.

The next day the bike went outside and with a couple of pints in the tank I pulled out the Bi-Starter for the first time and kicked. After creating an enormous bruise hitting my calf on the oil tank cap I kicked again and off she went – running, second kick!

Shaking Down

The first few rides were plagued by fuel level or air lock problems in the fuel lines. The bike would run for a while, enough to ride around the block a couple of times and then conk out just as you were passing a crowded pub on a sunny afternoon. I'd fitted a filter in the fuel line, complete with a sight glass like the one shown in the picture. Every time it stopped, you could see that there was no fuel getting through so I congratulated myself on fitting an effective filter with a sight glass. I convinced myself the poor flow was down to fuel level & the high position of the float chamber until I realised that my filter trapped air bubbles and required a lot of pressure to allow the fuel to pass… It came out, replaced by a shorter piece of plain pipe and a simple gauze strainer in the carburetter banjo – the standard Ariel arrangement in fact. You have to be careful with these filters - there does not seem to be much resistance to flow but really they are better suited to pressurized fuel systems.

Whilst fuel supply had resulted in several unscheduled stops, the carburettor itself had been fine. On the advice of various club members I had fitted a coil spring to return the throttle, replacing the Ariel volute spring design with something with less friction. Since I installed this spring, I have added a small plate to allow me to adjust the torque exerted on the spindle and head the tension in the cable – and the pain in my wrist. The bike idled quite smoothly from the start, but the mixture always appeared a little rich – I’ve adjusted this since and all seems fine, though on very hot days I believe I develop a misfire.

The first few trips had me adjusting the brakes every day. It’s important to realise that you use the square wedge brake adjustor first, then the cable or brake rod; then the brakes bed in nicely. The rear has a lot of feel, a long lever and is quite effective; The front, at least initially took a lot of lever effort and felt quite dead. A long trip into the country gathered something in the brake drum: a chunk of grit hard enough to write off the linings and seize the brake on. It was a shame that I didn’t notice the smoking drum until the grease had melted and flowed out of the hub…

Charging looked good on the ammeter from the first day. All the lights worked perfectly, apart from one indicator which persistently rotated around to face the floor, but the running in routine, short trips around town & a few longer trips into the country were to prove the need for a larger generator output. The Lucas C35SD gives 70 W at about 1700 rpm which equates to 32 mph in top gear, but when you are running around town the ignition, brake light and frequently used indicator loads soon drain the battery, which appears as a fuel-starvation-like misfire until it stops altogether. I cursed that fuel line again until I realised what was going on. Actually, you need about 20 W for the ignition alone, or about 3 Amps; in top gear, you get 3 Amps from the generator at an average of 23 mph – these bikes are really not for town use. You can understand why they fitted a bigger battery for 1951.

I had a couple of issues with the speedo: the first was a complete lack of function after one trip. A quick look at the cable had me wondering where the inner wire had gone – it had dropped just out of sight into the outer but was still turning. A look at the other end revealed that you can fit the cable into the BA gearbox in two positions, one maybe 3/8” higher than the other, resulting in a cable disengaging from the drive pinion in the speedo head. The second was less easily fixed, and manifested itself as a needle which would sweep around to 120 mph and stay there. This was down to poor lubrication in the main spindle, which I fixed and promptly caused another problem – over lubrication causing the speed movement clutch to slip. Result? Speedo sweeps around to 120 mph and stays there…

I’d read about the difficulty of getting the BA into neutral at a standstill, but I wasn’t prepared for difficulty changing gear as well, accompanied by a suspicious drop in revs – there was something amiss with the clutch. After the first few miles I stripped the clutch down again, and made a better job of dressing the splines on the clutch centre, making sure I had every last trace of damage removed. The result was a silky smooth clutch with a very progressive take up, which I am told is the norm for cork lined clutches. Apart from selecting first from a standing start, the gearbox is quiet and the change is very smooth.

It’s still hard to engage neutral at a standstill.

Which leaves the engine. Initially very stiff, even with the 20W/50 oil I was using, the engine eased off quickly. The bottom end is quiet and the whole experience is very smooth. She started beautifully, coming off the bi-starter after a few minutes and settled at about 25 psi oil pressure at idle, which I was very happy with. At the time, I was gaining confidence doing little 3-4 mile trips around the local streets, just to get some confidence.

That’s the end of the good part.

After about 50 miles, it was time for some engine maintenance – the tappets were noisy and I needed to re torque the head. There were a few small oil leaks around the head gasket, so I pulled the nuts down a little more, maybe a 1/4 turn on each - except the little reduced-hex guys between the rocker boxes. These guys are only hand tight. Now I know I made a better job of that when I pulled them down the first time...

So I worked around the head and the base gasket, pulling everything down. I also replaced the rocker cover studs, one of which was badly stripped (at the nut, not the head, fortunately!). Since all the plugs were out I bent the HT lead terminals a little more to improve the HT cable routing. I also sealed the exhausts at the cylinder head with high temperature silicone sealant, so hopefully we won't have any more exhaust or oil leaks.

I then started extending these trips into 8-10 mile country routes, getting up to 40 mph; returning after one of these I was aghast to find all my oil pressure gone! I rode the last 250 yards home very gingerly.

The first step was to look at the oil pressure relief valve spring, which I replaced with a new one. This resulted in cold idle oil pressure leaping up to about 55 psi; at idle, you could see the oil coming from the relief valve by removing the front crankshaft inspection cover. After a 5 mile run, the oil pressure was down to 25 psi, and the relief valve was holding pressure.

I changed the oil. I knew that after about 5 miles the oil temperature was around 75°C, and I knew that whilst 20W/50 and SAE 50 have a similar viscosity at 100°C, at 75°C the SAE 50 oil should be much more viscous, resulting in higher oil pressure. Changing to SAE 50, I could now travel about 8 miles before the oil pressure dropped to 15 psi or so. Still not good enough.

During the build, I had replaced one of the rocker shafts due to a damaged thread. I knew that the others were worn, but not very badly – looking for ‘low hanging fruit’ I replaced these too. This didn’t make an obvious difference, probably because the flowing area of the rocker oil feed pipe is smaller than the flowing area of three worn rocker shafts, so it is the pipe that restricts the flow and generates the oil pressure and that parameter had not changed.

My fear was that the big ends, which I had not reground (afraid of generating stress raising corners in the journals) and which were on the low side of acceptable were causing a loss of pressure, and they probably are.

However, a couple of things: one, that folk tell me that Square Fours run very hot especially during running in, and two, that getting heat energy into the oil is difficult. An 8 mile run showed me oil at 95°C – so it was surely getting hot. Maybe my loss of pressure was caused not so much by excess wear, but by low oil viscosity derived from excess temperature?

I started to look at overheating issues in air-cooled engines (the VW owners have a lot to say about this) and discovered that retarded ignition timing is a common cause of overheating. I readjusted the timing, advancing it quite considerably and found a lot more urge and cooler running. I could now get to about 17 miles before the oil pressure gauge became too uncomfortable to look at, and this is still the distance i need to ride to get it fully warm today.

Next stop was the valve timing. It is known that Square Fours will run with valve timing around 25 degrees out, so I checked mine once again. Its relatively simple to adjust the valve timing since if you remove the dynamo sprocket, you can adjust the position of the engine sprocket without removing the oil pump, which was a good thing because mine was more retarded than it should have been.

The result was quite encouraging. Since I had been in the timing chest and disturbed the dynamo sprocket I had to reset the ignition timing again, but the engine was much smoother and the idle much better. Throughout the running in period, I monitored the cylinder head temperatures along with ambient temperatures and the time spent on the road, and I found that contrary to popular belief, the rear cylinders don’t in fact get much hotter than the front. I’m now using Penrite Shelsley Heavy 40W/70 which keeps the oil pressure at a comfortable level at all times – but I have to ask my pet Gorilla, Nigel, to start it for me in the winter. Either that or roll it down the hill.

More recently, I have found that the cylinder head/pressure gauge oil line assembly which I bought was in fact incorrectly though logically manufactured. Correcting this problem, which involved swapping the two lines (the large line feeds the gauge; the small line acts as a flow restrictor and feeds the rockers) results in a more responsive gauge, less leakage at the top end and more oil pressure at the bottom end. With the next change I will probably go to Penrite Shelsley Medium 25W/70, which should make it easier to start in the cold.


As you will have realised from the first part of this article, these bikes are prone to getting quite hot. We have air cooling, but for various reasons this is implemented in a questionable way so we need to think about how we can improve that. The obvious way is to improve the cooling using the lubrication system, so to start with I have fitted a Morgo oil pump and an oil filter. The idea is this will allow more oil to circulate around the engine, splashing out of the big ends and hopefully picking up heat from the pistons and cylinders. The oil then passes into an oil reservoir and filtration system that has increased volume and a small increase in surface area.

Leaks have certainly been an issue, from the cylinder head gasket mainly, but also from the base gasket and rocker spindles. This has not been helped by a casting fault around the cylinder head nuts in front of the carburetter, which means you cannot get a ring spanner on those nuts.

The oil filter is hidden under the gearbox, between the frame rails and is lifted up as high as possible to keep it out of harm’s way. It's plumbed into the return line from the engine, so that I can fit an oil cooling radiator if I need it. Another option would be to fit the oil spray bar from Iron Horse Spares, but I'm not sure that I need that yet, since I seem to be getting heat into the oil quite successfully. On the two occasions I have measured oil temperature, I have had tank temperatures of 73°C after about 5 miles of town riding and 95°C after 17 miles of rural riding – enough to shake off any condensation.

I made a lot of changes to the electrical system, as I usually do with my restorations. I tried to keep the wiring and harness coverings in period, using black rubber covered wire (it's used in solar panel installations) with short coloured sleeves to identify the wires. The idea was to make everything look as though it could have been there in 1951, but the indicators are a bit obvious and I'm not sure I'm happy with them. I find myself using may arms as well, fairly convinced that a dayglo yellow arm is more obvious than a blinking light, though not much use at night of course.

Another important electrical modification is the Lucas 529 rear light. The 529 was introduced to replace the Lucas 480 originally fitted in 1951, and fits in the same holes. It's a lot larger, and safer, than the 480 which has about as much light output as a penniless students bicycle. Mine has a LED stop tail lamp in it from Paul Goff, which reduces the load on the battery. I have LEDs in the speedo and parking lamp as well.

The charging system uses the standard Lucas generator, running at 6V into a 2-Reg regulator/rectifier (again from Paul Goff), charging two gel batteries in a replica Lucas GU11 battery box from Draganfly. Also crammed into this box is a 6 way fuse box from VWP, which is wired to protect all the major circuits.

Rightly or wrongly, I’ve used stainless fasteners throughout the restoration – mainly due to the fact that I had virtually no fasteners in the boxes of bits. I know these add a lot more ‘bling’ than would have been seen in 1951, but my machines are for using and they live near the sea a lot of the time.

Riding impressions

Make no mistake, I love this bike. It’s brought a few challenges but it has been a big part of my life for quite a few years.

It’s easy to start, with quite low compression and coil ignition. It comes off the bi-starter after a couple of minutes of warming up; you put the bi-starter in the mid position to ride away and after a few minutes riding you can close if completely. The engine is very smooth and has a fabulous exhaust note. The smooth surge of power is phenomenal, and it will famously growl away from a walking pace in top gear.

Apart from getting into first, which even Ariel recognised as an issue (there is a section in the Owners Instructions about getting it into gear noiselessly) the gear box is quiet and easy to change whilst on the move. Getting it out of gear whilst stationary is another matter. Good luck with that, and remember to engage neutral before you stop next time!

It’s a big, comfortable, roomy bike which is low enough to get both feet on the ground easily; and as they say ‘the controls fall easily to hand’. Despite the lack of damping at the rear end, the bike has a very stiff frame and a low centre of gravity. It will drop into slow corners easily and it is an absolute delight to experience winding it upright again & out the other side on a surge of torque. There’s a lovely downhill S-bend around a farm near here – you drop down the hill on the overrun with this lovely deep roar from the exhausts, flip the bike over and power out uphill, engine growling beneath you. It’s magic.

Initially the steering appeared to wander a bit if the damper was remotely tight; in fact, as I developed an understanding for where the tyre pressures ought to be (harder up front, softer in the rear), the problem disappeared. I think the back end does adversely affect the steering – It doesn’t wander, just feels a little uncertain... I’d also left the head bearings looser than ideal.

The second thrill is the torque, and roundabouts. You’re humming along at 40 mph or so, slow up a bit to check for traffic, then it’s a quick left, right, left as you whip around the curves, open up again and once more you are humming along. No fuss. I love it!

Phase 2 Chrome, carb & paint

At the beginning, because Amelia was a basket case I planned a two phase rebuild. The first phase was getting it up & running & riding; the second phase would be cosmetic. I didn’t manage that too well (look at the nicely finished wheels) but there are a few items that haven’t been touched yet, including the black paintwork. Since being back on the road, risen from the ashes or more accurately, like so many others, from a dusty shed I have fettled & fixed & serviced various parts.

A year in, I replaced the fork bushes, happy to find that I have later stanchions with improved damping; the improvement in handling was substantial, though the one fork leg did seize a couple of times helping me to understand what the London-Brighton riders feel like on their suspension-free machines.

An odd problem occurred with the front brake, which would seize frequently, overheating the drum and liquefying the grease – an interesting experience, tolerable in the Norfolk countryside but not to be recommended on the motorway. The various brake rebuilds saw me replace the chrome back plate sooner than intended, but all has been well ever since; the wheels now have sealed bearings.

A new fuel tank has arrived to replace the KH tank I fitted and painted at great expense - it's in first paint but is not too happy. The badges have been replaced with originals in better condition, with their chrome ‘wings’, along with one or two other shiny parts such as the air bell on the carburetter. The carburetter has its proper bi-starter parts now. The carburettor also decided to ingest some fluff from somewhere, which lodged in the pilot circuit and caused some fun with hill-starts and slow corners.

Amelia has been joined in the workshop by a W/NG, which is going to be the subject of another article or three and has an interesting continental past. The next, longer range jobs for the SQ4 will include chrome plating the fork top nuts, and wheel spindles, making a lower chainguard and dealing with anything else that crops up. I’ll do those as I go along, but right now the main thing is to accumulate some more miles and enjoy the summer ride all of which, and my workshop exploits, will be recorded on my blog at


Thanks are due to the great folk at Draganfly; John Mitchell; Bernard Ashpole, John Spurgeon at Aerographics but most of the thanks go to all the guys on the AOMCC forum, without whose help & guidance this project would have been a lot more difficult & much less enjoyable.

Waiting to go home


  1. Wow! A tour de force description, interesting and very informative. Thank you for sharing your interests with other readers.

  2. brilliant job !! congrats! am starting to update a pristine 1955 mk 2.

  3. Just to confirm, with the oil pipes the larger should go to the gauge and not the the rockers. I'm trying to fit an oil pump on my mk11, I've managed to get mk2 pipes . I was told the SNL to the gauge and the larger to the rockers

    1. Can I suggest that you join the AOMCC forum and post this question. It's one that warrants a bit of discussion to get an understanding of how you tube up the gauge and the rockers - and bear in mind, my bike and my experience is with a Mk1, not a Mk2.