JJ2S X4 500 – 4 Cylinder 2 Stroke Concept Motorcycle

JJ2S X4 500cc 2 Stroke motorcycle

Motorcycle design often revolves around the engine. The size, shape, number of cylinders and configuration play a large part in much of what follows. What if you had an X4? 4 cylinders in an X configuration open up new design possibilities and that is exactly what we have here, not only that, it appears to be a 500cc 2 stroke! This is the JJ2S X4 500 by JJS Design. They have developed and patented a new engine and designed a motorcycle around it.

JJS Design is a Polish company and unfortunately my translating abilities here are not so good, so I can't fill you in on many details but the design looks extremely impressive, both the motorcycle design itself and, of course, the X4 2 stroke engine.

I will try to get a translation of some of the information, any of our Polish readers care to lend a hand?

Thanks for the tip, Brian!

Lots of images below:

Link: JJS Design

JJ2S X4 500cc 2 Stroke motorcycle

JJ2S X4 500cc 2 Stroke motorcycle

JJ2S X4 500cc 2 Stroke motorcycle

JJ2S X4 500cc 2 Stroke motorcycle

JJ2S X4 500cc 2 Stroke motorcycle

JJ2S X4 500cc 2 Stroke motorcycle


  1. hpfabe says

    I speak Polish, though it’s more conversational than technical. On the other hand, I am an engineer. I’ll try and provide a translation over the course of the weekend.

  2. says

    I have an echo chainsaw with two opposed cylinders that share a common crankcase area. This two stroke looks to have separate crakecase areas for each cylinder. Must get pretty complex keeping the crank transfer areas apart but common.

  3. curt says

    Great looking model, what are they going to do about the expansion chambers, this looks as though it uses exhaust off a four stroke. Also looks a little top heavy, given the amount of mass above the counter shaft location. Best of luck, cool looking project.

  4. says

    The exhaust seems unresolved in this concept. Four expansion chambers large enough to accommodate 125cc combustion chambers seems to be overlooked.

  5. says

    This is actually a 3D render. All of these images. As far as I can tell there is no physical prototype – at least not in this bunch of images. I am a 3D artist by trade, and there are many signs that this is a render. Maybe the concept is cool, but I doubt there is a real prototype.

  6. todd says

    an X-4 two stroke could share a single crankcase as long as the pistons all travel towards the crank center at the same time. That would tend to suggest a crank with four throws and the necessary cylinder offsets.
    The four separate carbs and no off-set do suggest four separate crank shafts. Maybe they are all gear driven to a central counter shaft. If so it’s not so bad. Square-four kawasakis had twin cranks geared together
    Regardless, this design should have nearly perfect primary and secondary balance.

    The velocity stacks, lack of air box, and megaphone exhaust all tell me this design is best suited to constant high RPM running.

    Very nice rendering, should be fun to build a prototype.


  7. todd says

    I need to clarify that the no off-set X-4 would have four cranks in four separate, sealed crank cases. That’s 8 seals.

    It would have been interesting to have the transmission in the center of the crank cases…


  8. says

    It looks to be a direct injection system that also uses reed valves to deliver fuel through the head, not from transfer ports from the crankcase. I am guessing this is how they manage to have such a compact, shared, crankcase. I also think that when you employ direct injection this way, you do not have the same issues of timing overlap with intake and exhaust ports, so you do not depend on the same type of tuned exhaust as a regular two-stroke. It is kind of like a four-stroke two stroke. Then again, I don’t read Polish and could be way off…

  9. Nathan says

    I fallen in love – thats the best looking bike I have seen since they first brought out the Ducati Monster

  10. says

    Haven’t you guys ever heard of a radial engine? I think that’s all this is, except it’s a 2 stroke, which would allow an even number of cylinders. 4 stroke radial aircraft engines require uneven cylinders (3,5,7,9,etc) to balance the firing order.

    And the single crank is totally doable in this concept, just like radial aircraft cranks, where the connecting rods all meet in a central hub.

    And I think it’s funny, these renderings are good enough that a few people thought it was a real bike!

  11. Skizick says

    Without a lower end squish happening there’s no way to make the charge hop into the combustion chamber, reed valves or no. The exhaust ports and the intakes look to be on the same plane. Coursion seem to be the only element usable. If the pistons go in and out in unison, why not one big carb in the center.

  12. mine says

    Hardly a new idea. Henry ford was experimenting with x shape car engines years ago but was never able to get them working well enough for production

  13. says

    So this is a four-cylinder radial, in other words. Or could be, anyway :-p

    I smell the bike in the next X-Men spinoff :-p


  14. bR1an says

    There are sooo many techno geeks on this site, and I mean that in the most complimentary way possible! Every time some new/forward thinking/outside the box design shows up, I can count on at least three or four uber brained technophiles to weigh in and send me into a frenzy of web searching which inevitably leaves me frustrated and, more often than not, actually knowing LESS than when I started.
    Thanks a lot.
    Rant over. I’m going to watch Robot Chicken and have a beer. Oh yeah, thats a wicked cool bike, rendered or not.

    (It’s been said before and I’ll say it again.. This hands down the best motorcycle site out there) Thanks Kneeslider

  15. ROHORN says

    I’m not Polish literate, but I can read drawings.

    It sure looks to me like a sleeve valved engine.

    More here to go by:


    There’s a lot that can be figured out by clicking around that site and browsing the illustrations.

    The crankcases aren’t pressurized to charge the cylinders. The opposing pistons seem to be connected to each other – the crank operates with an eccentric.

    Another drawing – there are LOTS of them:


    Which came from:


    In addition to more pictures, page 51 has the engine cycles illustrated:


    Note the balance tube between the crankcase and the top of the piston/sleeve/? chamber. The cases have nothing to do with charging the cylinder.

    I’ve seen these referred to as stepped piston 2 strokes….

    Here’s a stepped piston 2 stroke:


  16. VMX1000 says

    Mechanically this engine would not be able to run at high rpm if you look at the very elaborate and heavy piston/sleeve combo design. You’d have some very high stresses on crank/rods, compared to a conventional two-stroke.
    And, yeah, expansionchambers are included under “the bare essentials”.

    Pretty cool rendering, cool :o)

  17. motoxyogi says

    Really nice concept and i would love to give it a try to see what it feels like. But i doubt it would be a performance engine in any way. The gearing system, assuming they use what rohorn suggested(by the way are two of the opposing cylinders offset? or the rods?), looks overly complex (the output comes out the left side of the engine and is then routed under the engine to come out the right hand side) and very heavy for the size of the bike.

  18. Tim says

    It is very cool but looks a long way from production. I LOVE two stroke road bikes, but it looks like the “concept” rendering of the RD500 which was in MCN and Performance Bikes is closer to production!

    Can anyone explain to this idiot why all this fuel injection technology can’t be adapted to a two stroke engine? One of the posts above alludes to it, but my very limited understanding is that in a conventional two stroke you kind of have to have the inlets and exhausts open at the same time, and some of the unburnt charge “escapes” at certain revs, leading to the issues with emissions. given the nanosecond control of fuel charge and the myriad electronic monitoring/controls available, why can’t I have my RG500Gamma (got offered one for $8k NZD the other day… had to pass) but updated for 2008?

    And sorry in advance for being a technical ignoramus: To misquote Leonard McCoy again “Dammit Jim, I’m a lawyer not an engineer”.

  19. ROHORN says

    There are plenty of fuel injected 2-strokes in snowmobiles, PWCs, outboard motors, etc…..

  20. says

    It’s a well known design in Poland, but still controversial. The constructor has to deal with lack of money and other problems, but he was already able to forge a running small scale model of the engine. We are going to put some info about this news on our webpage with a request for help with translating. We hope that somebody will be able to help. Good work after all.

  21. Lechu says

    I am from Poland and I’ll try to explain how the engine works. It is a bit complex. Basically it works as a 2 stroke – each cylinder delivers power once a turn of crankshaft. However the crankshaft and the crankcase are closed and lubricated normally with dry sump system as in 4 stroke engines. The X4 engine is combining the efficiency of a 2stroke engine and it has reduced pollution.
    Furthermore the engine has less vibration on high rpm than in lower rpm. It is using a special crank design.

    The prototype of this engine is actually working – they have build a small, one cylinder 5cc engine to prove the design is good, and the small engine is fully operative. Now the are working on a 125cc version, and after that they will try to build the X4, 500cc, ~100 HP version. It will be equipped with direct fuel injection system.

    The motorcycle itself is estimated to cost about 20.000 – 25.000 $ .

  22. Lechu says

    I would like to add something. The basic design of the engine is similar to a big, marine, diesel engines. Those are also two stroke but they are lubricated in a normal way, as in 4 stroke engines.
    The main difference is that those big ship engines need to be supercharged to work. And the X4 engine has a special self-charging system. The air and the fuel mixture are pre-charged there and when the piston opens the port it rushes into the combustion chamber and the exhaust gases leave. Then the mixture is compressed, ignited by a spark plug etc.
    To fully understand how it works you need to visit the website.

  23. Justin R says

    Oh, thanks ado!
    I was having a hard time between free translators and the site. You’re link may have solved my squabble.
    It looks to me like they may have an opportunity to create an engine around an engine.
    It’s already bizarre, but a quasiturbine would fit into it perfectly. Just due to the contrast and negative spacing of the video, I can’t tell for sure what ‘pieces’ make up the shaft in the center.
    Surely a quasiturbine in the center with separate small injectors would give it the extra power ppl want out of it… perhaps it’d run WAY too hot :/
    I thought I saw somewhere a beefed up apex seal equivalent, but it’s hard to say where it’d go since its all in Polish.
    I love the bike, if only it had a big Ducati Sportclassic lamp up front, it’d have my name written all over it. Perfect blend of ergonomics, modern tech and classic cafe racing beauty.
    As much of a believer as I am in this bike and as eco conscious as I am too, for $20-25k I must give in and pollute the small percentage more to save at least $15k. Sad times we live in, eh?

  24. mr nice toyz says

    this bike is cool i love the Bimota v due the thought of the classic gp 500cc two strokes just gets me exited all that torque and high revs. as far as this bike is concerned i do like the simplicity but that front fairing is to top heavy. it looks interesting but doesn’t fit the bikes design.

  25. MSW says

    That X-4 looks simular to the old Bourke engine. That is it seems to be useing a scotch yoke type joint on the crankshaft instead of conventional connecting rod. In the least the idea seems simular.


  26. jp says

    Wow, that’s a blast from the past. My grandfather had several of Bourke’s engines, but sold them off a number of years ago. He had successfully run them on a stand, though not mounted in any vehicles.

  27. Chris Goodchild says

    Very interesting concept! At high revs as someone has already said it should have low vibration, also with the sleeve valve design the way it is there is potential for high revs and rev equal power. As far as injection goes I haven’t figured that out yet but Aprillia have as far as I know, sorted a low emission injected 2stroke about 2 years ago with the help of an English engineer.
    I have just found this site, Brilliant! The comments are good and the commenters are mostly pretty bright . Thank you everyone.

  28. Rick_A says

    I think it’s an awesome and great looking concept, but the bottom line is that it’s a bit pricey and complex for a 100hp motorcycle. An advantage may be lighter weight, but it looks like the weight distribution is less than ideal; holding a lot of engine weight so high. The swingarm angle is also ideal for a cruiser but not a bike with sporting intentions. I do hope it sees production as production motorcycle design as of late continues to be more evolutionary than innovative.

  29. Jeremy says

    Looks quite interesting. But is it really a two stroke the reason I ask is the lack of expansion chambers on the exhausts.

  30. Andy Juza says

    The advancements in two stroke motors have become so far advanced, way beyond your banshee and blaster days. there is no need for expansion tubes on the motor. This motor is built with precision. Not like the japs do it. If you put enough time and effort into designing a two stroke motor, you will find that expansion tubes are unnecessary.

  31. Rick_A says

    IIRC it’s essentially a fixed piston sleeve valve motor, THAT is why it doesn’t need expansion chambers.

  32. bgi says

    Design of motorcycle is based on very old polish construction made in about 1920.
    The engine is amazing. 4 cylinder will work with very low vibration, it wont burn oil with fuel so will be safer for environment. it’s self charged and have direct injection so no fuel will go to exhaust unburned. it’s small – cross about 40cm – 16″ long and 15cm – 6″ depth, and should be light as ~ 45 kg (100 lb) but with 100 HP and 500ccm volume it’s just 30,5 cubic inch.

    fantastic 😀

  33. Andy S says

    I’ve just stumbled onto your site which is fantastic – thanks!Who cares whether the bike is real or not;it’s an absolute work of art.Similarly,how cool is the Harley 4 valve big twin sportsbike?Simply superb

  34. Andy J says

    Another reason why you do not need expansion tubes because they do make fuel injected two strokes. Take a look at a mercury optimax or a fict outboards.

  35. onsitewelding says

    Does anyone remember the RZ-350 sport bike? The Kenny Roberts endorsed production bike by Yamaha.
    Fast as a scalded dog! Would beat ninja’s etc three time the displacement.

    Been there done that. Cool rotary engine design tho.

  36. Mikus says

    Polska Kwidzyn Z tego Miasta pochodzi ten projekt.Pozdrawiam wszystkich smigających po sajdłokach

  37. Dave says

    Check out the radial four aero engine at http://www.zoche.de.
    This is a 2 stroke diesel (horror) with huge potential, but I think stalled by the aerospace homologation costs. But don’t let the diesel bit put us off….
    They use simple piston ports, dry sump crancase with no air or fuel breathing through, so its clean.
    They have a high geared turbo blower to feed air at low revs. This doubles as a compressed air starter. It has no starter motor!!!
    A normal turbo feeds air at high revs so no spannies. That said once its started the gas flows alone should keep it running. Outgoing exhaust can drop the cylinder pressure below ambient so some air will naturally flow in. I guess not enough for clean running – hence the blowers.
    They have fixed piston ports and because mega reliabity is an aircraft must-have it only revs to 2,500. But diesels give a flat torque curve and can go to 4000. The Zoche gives 150bhp from 2.5 litres running at 2500rpm. If it was revved to 4000 it should be close to 250bhp = 100 per litre. This is all with simple mechanical fuel injection.

    Now add in some modern common rail injection and electronics and who know how much power it could make. Having no crankcase pumping losses or narrow power bands to worry about its probably capable of doubling the bhp of the 4 stroke with the same capacity. Modern car diesels are close to 100bhp per litre so who knows what an automotive Zoche could be capable of.
    Now add some inlet reed valves, exhaust “power valves” (a la RGV or Elsie) and burn petrol. The biggest issue would be the huge radiators needed to keep it cool.!!!
    Mechanically all four con-rods are mounted on a single crank pin. Its like two Ducati V twins back to back. There is no master rod like a 4-stroke radial. There will be zero vibration and four firing pulses per crank turn.
    At 4000rpm it will be firing at the same rate as a 4 stroke four doing 8000. In basic tune this drops into Yamaha Diversion 900 and Honda CB100F territory. But with no camshafts no carns no poppet valves its less complex and lighter – even with a turbo.

    A bike could be light weight and amazingly efficient so would need to carry less fuel.

    I want one. Has anyone got a few £million do develop a working product.

  38. Andy J says

    You do not need reed valves for two strokes any more. they do and have been fuel injected for many years.

  39. Big Sven says

    I’ve not delved deeply as of yet, but the X-4 does resemble the ill-fated British Lottery bike of the 60’s, the entry sent in by an ex-RR engineer, loosely-based on a design of a top-secret 24 or 48-cylinder 2-stroke engine RR were making for the Dam Busters, so they could haul the 10 ton bombs up a bit higher. Secret, for Beaverbrook had banned any development other than Merlins, and the RR-engineers risked a firing-squad! This is also why the Whittle engine was delayed, without Beaverbrook we could have had Spits with jet-engines during the Battle of Britain! (Westland Whirlwinds, actually, a little-known twin-engined single-seat fighter that was rumoured to have been designed around a proposed smaller version of the Whittle engine). The secret RR engine was said to have rigid conrods, integral with the opposing, minimal, pistons – and thus very light – and the crank span like a camshaft, moving each piston unit to-and-fro, thus the internal friction was minimal. Much like a ‘Scotch-crank’, but better. The only engine they made ripped propellers to bits when the throttle was opened, so rapidly did it pick up, several 617 guys (who I knew) witnessed this. It was a pneumatically-operated, blower-fed, sleeve-valve, and no bigger than a Merlin.

    The winner of the lottery for the ‘people’s racer’? BRM, I think, the car people, and it was to be made by Velocette, I think. It was never made and the money dissappeared. The X-4 bike was laughed at. It seems the RR-engineer was making a bike himself, at home – it was seen by a neighbor just before he moved – but, when he checked a few years later nobody knew what happened to the bike or the engineer.

  40. Brian says

    Nice concept and design except why is the exhaust not set up with exspansion chambers? If it is a true Two-stroke engine it needs to have these!

  41. Brandon McCanna says

    Hey, My name is Brandon, and a couple months ago I designed an X motor of my own, but it is an automobile application. If you’d like to lend a hand to the next supercar feel free to email me and I’ll give you the details. Brandon_McCanna@hotmail.com

  42. Brock says

    Awsome bike! I love two strokes. I’m with everybody else, it looks like a 4 stroke exhaust. But remember people, the Polish invented and built the expansion chamber!!

  43. Dave says

    During the late 1930s Rolls Royce were commissioned to make a “persuit” engine. It was to be tremendously powerful with no regard for fuel consumption because it would power short range interceptor planes.

    The result was the Cecy sleeve valve 2 stroke which never actually flew but the War Ministry engineers estimated it would have made 2,500 bhp from a smaller capacity and much less weight than the Merlin which at the time was doing about 1/2 that. Crecy used a 2 stroke engine design pioneered by Henry Ricardo. It was nothing like a bike engine with no expansion chambers or any sort of crankcase breathing like bike engines.

    However, because the Merlin turned out so much better than expected (almost) all of RRs time and talent went into merlin development and the Crecy got ignored. It had fantastic potential but was eventually overtaken by the turbojet and never got off the testbed.

    Apart from its brute power, the Crecy was also amazingly economical on fuel. It used direct injected petrol into a stratified charge combustion chamber. Rich mixture near the spark plugs but virtually pure air further down. The fuel pump was a modified diesel injection pump.

    The Crecy had a normal sump like a 4 stroke with piston ports for the exhaust and a moving sleeve for inlet air. Its a shame they didnt appreciate that they did not actually need the sleeve valves. As long as the exhaust opens first the gasses will be gone by the time the inlet port opens, so both can be in the cylinder walls.

    Direct injection, stratified charge, turbo and mechanical blower all done by Henry Ricardo in the 1930s.