UP IN SMOKE

If you’re a two-stroke nut then chances are you’ve spent the last decade or so cry­ing in the cor­ner of a dark room, but there’s a glim­mer of hope that you may not need to cry much longer...

Fast Bikes - - FEATURE - WORDS: NEIL‘ KNOW IT ALL’ CHARLTON IMAGES: F BAR CHIVE

It’s been a long time since any ma­jor man­u­fac­tur­ers cranked up the pro­duc­tion lines and wheeled off a stro­ker, with Ca­giva’s SP 525 hooli­gan learner bike be­ing one of the last ex­am­ples to make it into the show­rooms. Yamaha were still pump­ing out their head­bang­ing TZ250 racer un­til quite re­cently, but un­less you wanted to share a prison cell with a hairy mis­ogamist named ‘Bob’, the race fo­cused weapon was lit­tle to no use for Her Majesty’s High­ways.

If you’re over the age of 30, chances are you grew up rid­ing a two-stroke of one ca­pac­ity or an­other, and it’s likely to have left an in­deli­ble mark on your bik­ing per­sona. Be it for their stonk­ing per­for­mance or sheer in­bil­ity to go for a whole week with­out break­ing down, twostrokes of­fered an ex­pe­ri­ence of sur­prise that kept most of us on our toes and filled our daily bore­dom with mem­o­ries of both the good and bad va­ri­ety. If you’re like me, as in slightly fat and bald­ing, then you’re prob­a­bly old enough to feel a cer­tain nos­tal­gia to Suzuki’s RG500, which I class as the last main­stream su­per­bike to have made it into deal­er­ships. The 250cc two-strokes en­joyed a longer stay of ex­e­cu­tion but the Ja­panese big four had aban­doned ’stro­kers and their fans by 1998. Luck­ily, Suzuki sold the de­sign rights to their RGV250 engine to Aprilia, who con­tin­ued to use a mod­i­fied ver­sion of the Suzuki engine in their RS250 right up un­til 2004.

Many afi­ciona­dos cite the lit­tle Aprilia as the purest two-stroke road bike ever made and 13 years on, the RS250 still looks and han­dles like a race bike that’s es­caped from the pad­dock. Which it is.

Re­turn of a full-fat 500

Aprilia were about to en­counter some heavy­duty com­pe­ti­tion to their pre-mix pow­ered mo­nop­oly. Bi­mota, pur­vey­ors of ex­quis­ite if quirky Ital­ian ex­ot­ica, took the risky step of de­cid­ing their first ever in-house de­signed engine should be a two-stroke. And not a tid­dly, lit­tle 250 like ev­ery­body had been push­ing for the last decade, oh no, they de­cided to go for a full-fat 500. In 1997, 10 years after the Ja­panese had turned their backs on big ’stro­ker lovers, Bi­mota un­veiled the V-Due.

The V-Due’s sales brochure read like a pure race bike: The bike’s 500cc, 900 V-twin engine was to be held in a twin-spar alu­minium frame, sus­pended with fully ad­justable 46mm Paioli forks and Öh­lins rear shock all wrapped up with mouth-wa­ter­ing Ital­ian styling. Bi­mota promised that the V-Due would de­liver a use­ful 110bhp punch with a 145kg wet mass. To put that into per­spec­tive, it was go­ing to weigh the same as the Aprilia RS250, but with twice the power (but at nearly three times the price). It seemed as though the pro­posed pro­duc­tion run of 500 bikes would be snapped up by (wealthy) two-stroke junkies as soon as they hit the show­room. How could Bi­mota go wrong with a bike that was go­ing to pack de­cent power in a top drawer chas­sis that weighed the same as a 250?

To an­swer that ques­tion, I’m afraid we need to un­der­stand a lit­tle bit about how two-stroke en­gines work and par­tic­u­larly why they’ve al­ways had a rep for be­ing a bit en­vi­ron­men­tally un­friendly. Un­like a four-stroke, a two-stroke engine doesn’t use valves to con­trol its air/fuel flow. In­stead, ports (holes) are cut into the engine’s cylin­der walls and the pis­ton acts like a valve as it slides past these ports. To be able to ac­com­plish a gas ex­change (out with burnt ex­haust gas, in with a fresh charge) in just two strokes, the ports that al­low fresh charge in (trans­fer ports) need to be open at the same time as the ex­haust port. So, you may be ask­ing your­self, what stops the fresh charge from just head­ing straight out of the ex­haust port then?

Well, noth­ing as it hap­pens. And here lies the first prob­lem of man­ag­ing pol­lut­ing two-stroke emis­sions. Not only does some un­burnt charge es­cape out the ex­haust (caus­ing hy­dro­car­bon pol­lu­tion) un­der cer­tain con­di­tions, a sig­nif­i­cant vol­ume of ex­haust gas stays in the cylin­der and ‘di­lutes’ the next cy­cle of in­com­ing charge. This is also bad, be­cause it causes the engine to

mis­fire un­til the engine has cy­cled through enough times to re­sult in a charge that can

be lit by the spark plug. This phe­nom­e­non known as ‘four-stroking’ also leads to un­ac­cept­able lev­els of hy­dro­car­bon pol­lu­tion. Now con­sider that tra­di­tional two-strokes burn their lu­bri­cat­ing engine oil along with their fuel and you can see why tree hug­gers hate them so much.

Lethal in­jec­tion

Got that? Now, back to the V-Due. Bi­mota took the in­cred­i­bly brave and no­ble step to take on the task of clean­ing up the twostroke and re-estab­lish­ing it as a vi­able bike engine for the fu­ture. They did this by equip­ping the V-Due with elec­tronic fuel in­jec­tion, a first.

The V-Due’s in­jec­tion sys­tem was dou­bly im­pres­sive be­cause Bi­mota took the un­prece­dented step of designing the in­jec­tors to spray fuel di­rectly into the cylin­der trans­fer ports rather than the engine’s in­take like a ‘nor­mal’ in­jec­tion sys­tem. Not only were Bi­mota brave and no­ble, they were sadly naïve and over­con­fi­dent to be­lieve they could mas­ter a prob­lem that had vexed the likes of Honda and Yamaha for over 30 years.

In­evitably, Bi­mota’s di­rect in­jec­tion sys­tem didn’t work. Sure, the V-Due passed Amer­i­can EPA emis­sions tests, but the bike was un­ride­able. The fu­elling was so bad cus­tomers uni­ver­sally com­plained, added to other qual­ity is­sues, Bi­mota had to con­cede that the bike wasn’t fit for pur­pose and of­fered ev­ery­one who bought a V-Due their money back. By 1999, the V-Due dis­as­ter fin­ished Bi­mota off. Only 340 ex­am­ples were ever made, 21 of which weren’t even fuel in­jected, they ac­tu­ally had carbs fit­ted in­stead. The clean two-stroke dream en­tered the mil­len­nium still-born. The les­son all ma­jor bike mak­ers learnt from Bi­mota’s great folly was to steer well clear of two-strokes.

Stro­ker of ge­nius

With the sole ex­cep­tion of Aprilia’s RS250, pro­duc­tion sports two-strokes were dead and buried by the new Mil­len­nium. Honda even killed off their rare and ex­cep­tional CRM250AR en­duro bike in 1999. The tech­nol­ogy con­tained within this lit­tle off-road sin­gle was pos­si­bly a twostroke’s best chance to clean up its act. The CRM250AR in­cor­po­rated tech­nol­ogy from Honda’s class-win­ning ex­per­i­men­tal 1995 Paris-Dakar EXP-2 two-stroke racer. CRM’s ‘AR’ stood for Ac­tive Rad­i­cal, re­fer­ring to ‘free rad­i­cals’ that are present in still hot re­cently com­busted ex­haust gas. The CRM250AR utilised this still ‘ac­tive’ ex­haust gas to spon­ta­neously ig­nite the fresh in­com­ing charge un­der cer­tain loads and engine speeds. In ac­tual fact, the CRM op­er­ated

much like a two-stroke diesel from around 10% to 60% throt­tle! The up­shot of this un­usual com­bus­tion strat­egy was that the CRM250AR was more fuel ef­fi­cient and tractable than an equiv­a­lent four-stroke, had cleaner ex­haust emis­sions and it weighed less. If Honda were pre­pared to turn their backs on two-strokes after in­vest­ing so much time and money in de­vel­op­ing their ground break­ing ‘Ac­tive Rad­i­cal’ sys­tem, you can see why other bike mak­ers con­cluded that two-stokes had no fu­ture. But not so fast, tree hug­gers; luck­ily for us two-stroke fans are a hardy bunch and thanks to a few fa­nat­ics, the engine that can boast dou­ble the spe­cific power out­put of a four-stroke, didn’t dis­ap­pear com­pletely. Although, not ex­actly ‘run of the mill’, a hand­ful of be­spoke Euro­pean en­gi­neer­ing firms de­cided to keep the oily flag fly­ing just to re­mind us all how weak four-bangers are.

The Swiss Big Cheese

Few may re­mem­ber Swiss GP rider Eskil Suter for his rac­ing ca­reer. But I doubt that both­ers him much, be­cause Eskil’s got other skills too. He is the brains be­hind Suter Rac­ing Tech­nol­ogy, the com­pany re­spon­si­ble for designing the Petronas FP1 and the Moto2 chas­sis that Marc Márquez rode to vic­tory in the 2012 600cc cham­pi­onship.

SRT also helped Kawasaki de­velop their ZX-RR Mo­toGP bike and they as­sisted For­mula 1 spe­cial­ists Il­mor En­gi­neer­ing with the chas­sis de­sign of their 800cc Il­mor X3 Mo­toGP bike. STR realised that their ex­per­tise shouldn’t be con­fined to a hand­ful of rac­ers. As a way to show­case their en­gi­neer­ing ex­per­tise and the po­ten­tial of two-strokes, STR are craft­ing a lim­ited run of (just 99) spe­cials called the MMX500. With cre­den­tials like the ones above, any road or track spe­cial SRT pro­duce should be good, right? They say the Devil is in the de­tail, which we’ll get to, but just look at the MMX500’s ba­sic stats – 195bhp and 127kg! Even with a 70kg rider, the MMX500 still matches the power to weight ra­tio of a mod­ern Mo­toGP bike.

To achieve this in­cred­i­ble feat, STR cra­dle their own hand-built V4 two-stroke in a fully ad­justable CNC ally frame and swingarm. Sus­pen­sion is top-drawer Öh­lins, wheels are forged mag­ne­sium from OZ, brak­ing is by Brembo, the cus­tom ex­haust ex­pan­sion cham­bers are ti­ta­nium with car­bon fi­bre Akrapovic si­lencers. The spec’ sheet is end­less. If you peek be­hind the car­bon-fi­bre body­work and un­der the car­bon-fi­bre tank, you’ll find a be­spoke fuel-in­jec­tion sys­tem with three in­jec­tors per cylin­der, such is the del­uge of petrol re­quired to fuel the MMX500’s mighty 576cc two-stroke engine. But to be hon­est, if you can af­ford the £94,000 pur­chase price, ‘The Beast’s’ thirst for pre-mix isn’t go­ing to worry you.

Legally fast

What if track days aren’t your thing, in­stead you want a vis­cously fast, light mod­ern ’stro­ker to pop to Tescos on or shave sec­onds off your com­mute? Well, fear not, the Ger­mans have got you cov­ered (al­beit only a very well-heeled 46 of you).

If you’ve fol­lowed any of the World GP Leg­ends races you will have heard of Ronax. Their 500cc V4 two-stroke race bike fur­nished Jeremy McWil­liams with a win

at the 2016 Sach­sen­ring Clas­sic races last year. In Jeremy’s hands, the bike was more than a match for the likes of Fred­die Spencer and Garry McCoy on their age­ing fac­tory 500 GP ma­chines. The sig­nif­i­cant thing about Ronax isn’t the fact that a small en­gi­neer­ing firm can field such an im­pres­sive bike in the World GP Leg­ends se­ries, no, in­cred­i­bly, Ronax’s 500 is avail­able as a road bike, com­plete with lights, num­ber plates and mir­rors. Pre­sum­ably to watch ev­ery­thing else on the road dis­ap­pear in. For a tri­fling £84,000 (plus tax), you can en­joy a full on, 160bhp, 147kg, 500cc GP bike on the road. Wouldn’t it be great if a ma­jor bike man­u­fac­turer would take the lead and try bring­ing the two-stroke up to date and to the masses in the way these spe­cial­ists com­pa­nies have for the su­per-loaded?

The good news is that a cou­ple of the big boys never com­pletely ditched the twostroke. Fair enough, Yamaha and KTM only make sin­gle-cylin­der off-road ’stro­kers at the mo­ment. But it proves that as far as MX and en­duro goes, the mar­ket for two-stroke thrills never com­pletely died. More­over, the ev­i­dence sug­gests a strong resur­gence in de­mand for ‘stink-wheels’ with en­duro rid­ers. Here’s the rea­son: Pro­vid­ing power at ev­ery stroke of the pis­ton gives the two-stroke engine ac­cess to huge po­ten­tial – not just sear­ing top-end power, but if tuned cor­rectly, also with mon­ster torque, right off the bot­tom. It’s not the top-end power that diehards love about the two-stroke en­duro bikes still avail­able from the likes of KTM, Husq­varna, GasGas and Beta, but the mon­ster torque avail­able at re­ally low rpm.

Even when bogged right down to tick­over speeds, these bikes re­spond with front wheel lift­ing torque. Cou­pled with lower weight, eas­ier start­ing and sim­pler main­te­nance, grunty, pow­er­ful two-strokes are just too good for ded­i­cated en­duro bike mak­ers to ig­nore. So good in fact, that rather than take the easy op­tion and aban­don two-strokes in the face of strict Euro 4 emis­sions reg­u­la­tion, KTM are equip­ping their 2018 250 and 300 EXC mod­els with fuel-in­jec­tion this year.

Secret stro­ker

By the time you read this KTM will have re­leased these new mod­els, and all the se­crets that come with them, but it seems the KTM’s set up has sim­i­lar­i­ties to the Bi­mota V-Due’s trans­fer port in­jec­tion sys­tem. This might seem risky, but trans­fer port in­jec­tion is nec­es­sary to meet ex­haust emis­sions tar­gets. How­ever, re­peat­ing the mis­takes made by the Ital­ian firm would be ru­inous for KTM.

So it’s no sur­prise to learn that test bikes from the Aus­trian maker have been spied com­pet­ing in en­duro events all over the world for sev­eral years now. The chance of it run­ning like a bag of span­ners like the Bi­mota did are min­i­mal, but even if this new breed of FI two-stroke off-roader cracks the dirt bike mar­ket, what are the chances of it lead­ing to new, road go­ing two-stroke bikes? Let’s not get too giddy about the thought of Suzuki un­veil­ing an all-new RG500 any time soon. First of all, emis­sions reg­u­la­tions are just get­ting stricter and stricter. For a high per­for­mance road go­ing two-stroke to meet Euro 4, it would need to in­cor­po­rate com­plex di­rect fuel-in­jec­tion, a di­rect lu­bri­ca­tion sys­tem (rather than pre­mix) and cat­alytic con­vert­ers in its ex­pan­sion cham­ber exhausts. If any two-stroke is still able to out­gun a four-stroke after that, the is­sues with pis­ton, ring and bore wear also need to be ad­dressed. Oth­er­wise ma­jor ser­vices to a ’stro­ker are go­ing to cost three times those needed for a com­pa­ra­ble four-stroke. And with money be­ing as tight as it is the world over, there’s lit­tle chance of any man­u­fac­turer head­ing out down that costly road.

So, get buy­ing those lot­tery tick­ets be­cause if you’re des­per­ate to be reac­quainted with some GP in­spired two-stoke ex­u­ber­ance it’s the likes of Suter and Ronax who you’re go­ing to have to turn to. And they’re not cheap. For the rest of us, we’ll just have to hope that some hard­core stoker fans find their way into the mo­tor­cy­cle in­dus­try and start forc­ing a hand to see this new and cleaner tech be­ing utilised on pro­duc­tion road bikes. Un­til then…

Can we have two please?!

Aprilia RS250s are bril­liant...

KTM's new di­rect-in­jec­tion stro­ker might bring hope for two-stroke fans.

The good old days!

The Ronax looks like an NSR500 clone, right?

If only these were £10,000 – sigh. These pair are now worth a small for­tune...

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