THE HISTORY BIT
The original Square Four engine was designed by Edward Turner in 1928.
He was trying to get work as an engine designer with a number of motorcycle manufacturers, using his unique engine design asa calling card to demonstrate his skills. The engine was considered by BSA but rejected. Ariel, however, liked the idea and decided to make it.
The early engine with two transverse crankshafts was essentially a pair of across the frame ohc parallel twins joined by their geared central flywheels, with a square, four cylinder block and a single head. With a chain driven overhead camshaft, the early Square Four 500 used a hand change, four speed Burman gearbox. The first Ariel Square Four 4F was shown at the Olympia Motorcycle Show in 1930.
In 1932,the cylinder bores were enlarged by 5mm to give a capacity of 601cc, specifically to accommodate owners who wanted to attach a sidecar.this model was used for the Maudes Trophy endurance attempt, covering 700 miles in 700 minutes, followed by a timed lap of 87.4mph.
The cammy engine gained a reputation for overheating the rear cylinder heads, so in 1936 the engine was completely redesigned, emerging as the 1937 ohv 995cc 4G.the crankshafts of the new engine were connected together by coupling gears on the drive side of the engine. In 1939 Ariel's patented Anstey link plunger rear suspension was offered as an option. In 1946, the plunger rear suspension was available again, with oil damped telescopic front forks replacing the previous girder forks.
In 1949, the Ariel Square Four Mkl saw the cast iron cylinder head and barrel replaced by an alloy head and barrel. Even with this 301bweight reduction, the 1949 machine was still no lightweight at around 4351bdry. The rather constricted and tortuous inlet tract, small valves, conservative valve timing, low compression ratio and car like combustion chambers all constrained power to 35bhp at 5500rpm. The Mkl, by contrast, was capable of 90mph plus.
In 1953,the four pipe 997ccmk2 was released with a re designed cylinder head to improve cooling and breathing, with four separate exhaust pipes from two cast aluminium manifolds and a rocker box combined with the inlet manifold. The frame was redesigned to accommodate the tall, car type Sucarburettor and the oiling systemwas updated with a gear pump which replaced the antiquated plunger pump. The Mk2's better breathing arrangements delivered 40bhp, and this Ariel was capable of 100mph (just). It weighed 4251band cost £336.16.6.
In 1954, Ariel built a Mk3 prototype with Earlesforks and swinging arm, but the model was never put into production. Over the years, various other swinging arm Square specials have been made.
The Square Four found a new lease of life in the
1970s when the Healey brothers produced the Healey 1000/4. The brothers tuned and upgraded Ariel engines for racing throughout the 1960s, and when
Ariel ended Square Four production they obtained a large assortment of spare parts. The Healeys updated the engine with a special camshaft, increased the compression ratio to 7.5:1 and improved the lubrication system. Power increased to 52bhp and the motor was installed in an Egli style frame, incorporating the oil tank, with Metal Profile forks.
The Healey 1000/4 was well received when launched at the 1971 Earls Court Motorcycle Show. It weighed lessthan the contemporary Honda 250, it handled well, and achieved a top speed of 126mph when tested. But it couldn't compete with the cheaper and faster Japanese superbikes of the 70s, like the Honda CB750. Production ceased in 1977 after 12 bikes were built, which means that the few surviving Healeys are highly sought after.
BUILDING IT
Eightweeksafter my Ariel left the Uk,it cleared custom sand abio hazard inspection. the stripped framewassoonon my benchand I wastest fitting the enginebottom end andgearbox.it didn't look right. the engine was can ted up by about 10degreesand,with the bend in the top tube kickingthe front forksout, it would have looked like it had saggedin the middle.perhaps the original builderwasgoing to fit longerforks or turn it into a chopper?on a positivenote the engine and gear box plates were OK.
After a lot of measuringand dithering,i finally got the angle grinder out. the first job was to cut the lower frame tubes just before they started curving up to get the engine and gearboxto sit level.thenextjob wascutting out the curved sectionof the top tube and installinga temporary sleeve.after a few tries I got the enginesitting leveland the restlooking OK.
I made some lower frame tube extensions that lined up with the lower mounting points on the frame plates, and tack weldedthem in place. Clampingthe front down tubes on the front engine plates,i measuredthe length of the slug for the top tube.theendsof the slugweremade
a tight fit in the frametube. Hourswere spent with a tape measurea, long steelrule and an inclinometer getting the top tube lined up before tack welding the slug in place.
With everything lined up, my attention turned to the engineand gearboxplates... knowing someof the frame holeswere now in the wrong place.drilling new holeswaseasy,but moving holes side ways involved a lot of filing and then filling the redundantpart of the holeswith weld. After severaltrial fits and double checks,the frame was professionally welded before blasting and powdercoating.
Next:the enginebottom end.
Takingit apart wasn'tthat difficult exceptthe two drive gears were a really tight fit, requiring a lot of heatand pulling beforethey cameoff.the only significant issue was the front timing side main bearing that had obviously spun. with new big end bearingsand bolts it all went together quite cleanly.the cylindersand pistonsweren't too bad and,after a light hone,somenew rings and improvisedring clamps,it all slipped into place.
Whileworking on the bottom end I could see glimpses of turner' s other famous design, the
Triumphtwin: the camfollowerslook identical.
The cylinder head was altogether another matter.all the studs had been repaired,one of the spark plugs came out with part of aH eli coil attached, and two of the valves were stuck open! Someof the stud repairswere badlydone,with He li coil inserts standing slightly proud and burrs around someother holes.the only sensible thing to do wasto removeall of the studs,fix the problemsand checkthe headwasn't warped (a common problem ). one of the studs came out with all the headthread still attachedto it. Hoursof work, dressingthe areasand Helicoils that were proud and makinga double diameter replacement stud, finally produced a flat cylinder head face. the valve guides were checked with a reamer(two weretight), all of the valveseats were recut and valvesground in.
Fitting the cylinder head correctlyis a long tediousjob, with 20 nutsto fit andtighten in a fixed order.the nuts hidden in the cylinderfins can be a bit fiddly, as is getting an eventorque setting on them all. Blowncylinder headgaskets havebeena problemwith Square4s, but the mo de rnotiosu per gaskets( available from Draganfly)and following the tightening down
instructions religiously can produce a good seal. The gaskets continued to settle so they were re torqued afterthe initial ridesduring running in.
The next challengewasthe Burmangearbox. None of the chain lines seemed to quite line up. Further checking revealed that it was the wrong gearbox,from a twin, with the input shaft modifiedwith a crudeadapterto replicatethe longer main shaft needed for a Square 4. I was not best pleasedw, ith a mutilated mainshaft
I am unlikely to recover anywhere near what
I paid for it. Thecorrect Square4 Gbburman gearboxesarelike hen'steeth. After months of fruit less s ear chingt, he correct box popped upon Drag an fly' second hand list. I have never been on the phonesoquickly.
The box slotted in perfectly and the chain lineswere much improved.a smallamount of shimminggot them dead on.i shouldhave stripped the gear box and perhaps questioned why it was a second hand box, but enthusiasm got in the wayandfitting the boxalloweda whole hostof otherjobs to be completed.
The primary chain ca seisin three parts. the front half of the inner cover is part of the drive gear cover;the rearinner chaincasebolts onto the front inner coverand a full length outer cover completesthe chaincaset. heouter coversare proneto damageandthe only one I could get had a broken engine shock absorb er dome. after cleaningup the damagedarea,a dome wasmade andwasglued in placewith epoxymetal.i did consider welding the geriatric die cast aluminium but it is extremely difficult to achieve a clean join. Thefinishedjob looksslightly different to standardbut doesnot lookout of place.
The cylinder head exhaust stubs were badly worn. weighing up different repair methods, shrinking on thin steel sleeves seemed the bestapproachand seemsto haveworked. Exhaust pipes were stainless steel square 4 pipesfrom Armours. Liningup the pipeswith the Hunt master frame and silencers took a few squigglybendsand a sleeveat the silencerends due to different pipe diameterst. he cut, shut and bent pipesare far from perfect and another set will probably be madewhen time permits.
The carburettor should be a Solex,but it came with theSu from a Mk2,soa conversion plate was madeto accommodatethe different mounting bolt positionsand borediameters.i have extensive knowledge of Amalcarbsbut knew nothing about thesesmallsusa. rebuild kit and a new dam per spring from Draganflywerea good start and it seemedto go together fairly easily.
The clutch cover was a mess.it looked like somebody had playedfootball with it. An hour's worth of panelbeating got it backroughly in the right shapeso it would fit (moreof this later).i hope to find a better one on my next trip to the UK.
Thelengthenedtop tube presenteda problem with the petrol tank; a standardtank was now too short. Fortunatelyi had a rather battered BSAA10 plunger tank that seemed to fit after cutting off the front mounting ears (easily replaced ). after blasting the tank to bare metal, substantialdents were pulled out and crackswelded up.the protracted processof priming, filling, rubbing down, priming, filling, rubbing down,etc,took a numberof cycles beforethe tank was readyfor a top coat.
At this point I should haveusedthe tank sealantbut applied it after the top coat, definitely a mistake! despite extensive precautions there was a small spill on the paint work. worse, the cling film usedto protect the paint finish caused fine markson the new paintwork.after another rub down andre paint, a local car painter applied a coat of two pack clear spray, the only finish that seemsto copewith modern petrol.
Thechangeto the tank alsomeantthat the seat had to be altered. rather than modify an existingseat,i madea new seatbase
out of 20mmply.a relatively simple bit of woodworking, with a fibre glass cover over the rear mud guard cut out. A local vehicle upholsters madean excellentjob of coveringthe seat,but I specifieda steppedseatwhich wasa mistake. It was too cramped for me. I subsequently had the seat recovered with a thicker flat top.
The bulk of the cycle parts are standard ariel items and didn't presentmuchof a challenge, particularly with the excellent parts avail abiil ty from Draganflyi. re spokedand trued the wheels, fitting Hi eden au tyres, with these mi rib bed K 44 3.25x 19onthe front andthe blockpattern K344.00x19ont he back. the classic hi eden au tyres, as supplied by Wheel house tyres, look the part and aremadeof modern rubbercompounds that grip well.
My first attemptsat startingthe machinewere not promising. the engine was rather stiff to kick over,with intermittent backfiresin the exhaust and theSu carburettor occasionally flooding. a quick checkwith the sparkplugsout revealed weakand intermittent sparks. Suspicionfell on the distributor cap: a good cleanhelpedbut it wasstill not right. Fortunatelya friend had a brand new austin 7 distributor cap, the same item as the Ariel. combined with a Magneticpowernz electronic trigger system produced excellent sparksat all the plugs.
After resettingthe carburettorfloat level,the secondattemptsat starting the machinewere an improvement but not by much!assoonasit fired there was sound like a fire bell going off in the primary transmission a. ft era quick shut down anda bit of headscratching, removingthe clutch cover revealed witness marks, confirming my suspicionthat the clutchwashitting the cover. Attacking the clutch cover again with panel beating hammer sand some washers under the mounting screws solved the problem.
Thingsweregoing better,but a quick ride up the lanerevealedthat it seemeda bit constipated.
It didn't sound right and neededquite a bit of throttle to tick over.i decidedto go backto basicsand check valveand ignition timing. Removingthe front crankshaftend coverto turn overthe crankshaft revealedwhy the engine had beenstiff to kick over.thecrankend nut wasrubbing on the end cover.somedeft work on the lathe soon fixed that. Turningthe engine over revealedthe ignition timings were spot on, but the plug leads to #2 and #3 cylindershad somehowbecome crossedover.with the leadson the right spark plugs she purred into life first kick,idled nicely and shot up the lanelike a scaldedcat.
To protect the freshly painted and vulnerable petrol tank, all the early tests were undertaken with a smalltest tank strapped to the top tube. After sorting the problems of fitting the tank and plumbing it in, the rest should have been a doddle ...
With four litresof fuel, however,there waslittle or no fuel flow. Initial suspicionfell on the fuel taps. Had I bought reservetaps with extended fuel pick ups? the taps checked out as normal, so I poked a drill up into the tank... to find a blockage. i suddenly remembered that these Bsatanks had separatefilters that screwedup into the tank these must now be coveredin tank sealant doh!
Initial test rideswere very promising. loads of smooth torque, comfortable sitting position and beautiful sound. Howeverthere were someteething problems.oil leaked profusely from the gearbox. rene wing the outer case gasket significantly reduced the flow, but it lookslike I should havereplacedthe inner cover gasket at the same time. the gear box is notably noisier in third, not an uncommon problem.it will be addressedwhen the box is takenapart to fix the oil leak.theclutch was dragging a bit but improvedwith adjustment, although it's still not right. Anotherjob to address when the gearbox is taken apart.the cylinder headstill seemsto be settling down, requiring the head nuts to be regularly re tightened.
Twiceunder braking,while turning right, the steeringseemedto lockand the front wheelfelt likeit wasabout to slideaway. Releasingthe front brakefreed up the steering.i spotted a witness markon the mudguardand the penny dropped. With the front forks compressedunder braking, the mud guard touched the left hand exhaust pipe,but this didn't happenwhen turning left. Another light bulb moment:the main part of the engine and cylinder block sits about two inches right of the frame centreline becauseof the crank shaft coupling gears. Slightly shortening the left hand pipe and bending it out to the left createdthe neededclearance.
The most painful part of getting the Ariel on the roadwasthe legalprocessof registeringit, involving government departments extracting large sums of money from my wallet. the first part of the process was al locating a 17 digit Vinand attachinga plateto the machine. The secondpart wasa'low Volumevehicle Certification' because of the frame modifications and engine change. The nearest motorcycle certifier is almost 150 miles away! the absence of a registration document meant applying for alternate document approval. the final part was a compliance check for an imported vehicle which duplicated most of the earlier tests, then registrationand a number plate.
Thefinal insult wasthat the registration authority insistedit be called an Ariel Huntmaster asthis iswhat it originally was!thetotal bureaucraticcost was £650,not including transportation and expenses...
TAKENFORA RIDE
Sowhat'sit liketo ride?turnon the petrol and pull up the enrichment lever on theSu ca rb, then a couple of healthy swings normally bring it rustling into life. It can be a bit cold blooded, so the enrichment lever is slowly lowered as it warms up. Oncefully warm after a short distance, the enginewill settle down to an eventickover.
Unlessthe clutch hasbeenfreedoff before starting, first goesin with a very definite clunk. Pulling away is extremely smooth, thanks to a progressive clutch and load so flow speed torque.
Accelerationis brisk,with none of the harshness usuallyfound with singlesand twins.gear changes are deliberate and best not hurried but, given the acres of smooth torque, this is not an impedimentto swift progresst. hefour certainly buzz es along and feels under geared. I have a sneaking suspicion that it is running on side car gearing and will change the gearing when I takethe gearboxapart.
The handlingis slightly on the slowside, just right for touring. the weight distribution, slightly longerframeand riding positionmake for a comfortable ride. the machine holds a line nicelyand is not easilymovedoff its line by bump sand pot holes. the exhaust pipes are slightlyfurther out than the Huntmaster'sand will touch down if pushed,but this is not the machinefor getting your kneedown on!
The only disappointing itemsarethe brakes. On paper,and lookingat the qualityof the shoesand mechanismt,hey shouldbe good, but they lackinitial bite. Don't get me wrong, they aremorethan adequatebut they promised more.i hada Bsaa10with the samebrakes back in the 1970 sand they were disappointing too. The Bsasingle sided8" brakefelt much better.i hope the brakes will improve after fully bedding down and further adjustment.
Most swingingarm Square4s usethe Mk2 enginewith the four exhaustpipes,so visually different to Mkl based machine st. hemkl with two exhaustpipesand its moreconservative looks can initially be confused with at win. I tried to emphasisethis conservativelook with the classicmauveand blackpaint scheme.
Wasit worth the all effort and did it meet my original goals?my answeris a resounding yes.thereareafew machinesthat you immediatelyfeel comfortable on and which give you confidence. despite a few niggles, this is one of those machines.if only the brakes were better, and maybe the engine could be a bit more powerful... Re