CLEAN AND MEAN: Two-Strokes Aren't Dead Yet!


MXEditor

All signs of life have faded…the two-stroke is dead.

Long live the two-stroke!

If you’re a powersports enthusiast over the age of 30 then you’ll remember when the two-stroke ruled the roost…and you’ll also remember when it all came crashing down. No matter what you rode on or in, someone stuck a new four-stroke engine in it.

Snowmobiles, boats, personal watercraft, off road motorcycles…you name it, the brap was going away.

But now in some areas of powersports the brap is trying to make a comeback. Cleaner, meaner types of two-stroke engine technologies are trying to claw their way into the showroom.

Two standalone research projects that caught our attention early on were the Omnivore and Grail two-stroke engines, and both helped keep the dream alive in some way, if even just to show that someone was trying to make two-strokes work.

In 2008, Queen’s University Belfast, Lotus and Jaguar developed the Omnivore, a two-stroke engine that featured variable compression ratios, which resulted in much lower “dirty” HC emissions and better fuel savings as a bonus. The engine was also said to use a monoblock design joining the cylinder head and block together, reducing weight and featured the Orbital FlexDI fuel injection system, reducing emissions and improving scavenging characteristics.

Around the same time we heard about the Grail, as both engines were referred to in the New York Times. The Grail apparently had some lofty goals (100MPG and a 1 liter design) but has so far failed to deliver a production version since they began.

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Photo Credit:

GrailEngine.com

Grail describes the engine’s operation in detail:

“Compression takes place within the reed valve air box, pre-compression chamber, vent-to-piston ports, piston-intake-ports & crankcase. As the piston travels upward creating a vacuum beneath the piston, fresh air enters via the intake air box through the one-way reed valve, and fills the external pre-compression chamber, vent-to-piston ports and piston-intake-ports with fresh air.”

“Compression occurs within the cylinder as the piston travels upward. At Top Dead Center (TDC), direct ignition then single or multiple ignitions occur. This forces the piston down into the cylinder compressing air in the engine crankcase, external pre-compression chamber, vent-to-piston ports and piston intake-ports. “

“Just prior to Bottom Dead Center (BDC), the exhaust valve opens via a standard cam/push rod mechanism or electro-mechanical valve control. Exhaust gases exit via the exhaust valve opening at the top of the cylinder. Compressed fresh air enters the cylinder via piston valve, which forces out the final exhaust. As the piston travels past BDC the exhaust valve and piston valve close and cycle repeats.”

More encouraging is the ongoing use of two-strokes in both snowmobiles and marine outboard engines. Even though most manufactures slated the two-stroke for failure and elimination from their lineups, a few hunkered down, listening to their huge client base and made the two-stroke more efficient and cleaner in the process.

Let’s look at some snowmobile technologies:

Ski-Doo claims that their Rotax E-TEC Direct Injection (DI) 800cc sled with both DI and precision oil-injection/metering technologies results in the highest HP/weight ratio as well as the lowest emissions in the 800cc class. This is a serious enthusiast engine with a strong following in this segment. See a video of the E-Tec in action HERE.

Polaris says their CleanFire2 Injection is the way forward. In this configuration, low emissions and high performance are the goals and Polaris uses a combination of DI technology but this time feeding the transfer ports, coupled with a precision Throttle Position Sensor (TPS) and proprietary Detonation Engine Technology (DET) to produce a fast revving sled that’s light with low emissions, but keeps a high HP/weight ratio.

And in the boating market:

You still find two-strokes still in the outboard engine segment, with Evinrude taking advantage of the E-TEC direct injection technology by its parent company Bombardier and successfully proving again that the DI/oil injection setup is perfect for lightweight power to weight ratio applications.

Mercury Marine has a strong lineup of what they call “two-stage DFI” engines that feature direct injection and also offer some measure of performance upgrades like carbon-fiber reeds and expansion chambers, while still burning cleaner than some opposition cc per cc in their class. Mercury claims the OptiMax 250 Pro XS burns 14% cleaner than some other 250HP four-strokes offered.

And then you have personal watercraft:

According to the PWIA, “Personal watercraft today are 75 percent quieter and up to 90 percent cleaner than pre-1998 models.” Now that’s an incredible statistic and shows that the PWC industry saw the end in sight and stepped up to the plate, the problem for two-stroke fans is that they pretty much dropped all support for the two-stroke and put their development efforts behind the four-strokes with great success.

But will these successful types of powersports two-stroke technologies make their way into off road motorcycles? Well a few manufacturers might think so as evidenced by these rumblings:

KTM - Highly efficient with a tremendous weight to HP ratio, KTM two-strokes don’t feature any type of space age engine technologies today, but you can be sure that KTM has been working on a DI based engine for the two-stroke range. These rumors have been bandied around in the off road press for well over a year now, although rumors that the engine is overly complex and may be almost the same weight as a four stroke powerplant are also rife, which may explain KTM’s reluctance to bring these variants to market.

KTM Product Manager Joachim Sauer recently stated in AustralasianDirtBike:

"We have been working a lot in recent years in order to get the injection system ready for our two-strokes. I went out into the market last year and visited lots of dealers and spoke to hundreds of riders and I asked them if they would like a two-stroke injected bike. Everyone said, 'Great! When will it be ready?'

"I then said, 'Would you still love it if the price was close to the 450/500 EXC?' Also, instead of just a carburetor and ignition, you would have to deal with pumps and all the complexities of such a system, which also adds 2kg of weight. It would make the whole thing so difficult to deal with you would not be able to change the piston at home anymore.

"From the beginning, I could see their enthusiasm get less and less, and at the end, out of 100 people I asked, there was not even five people who would like such a system. So we decided we won't introduce it until the rules (homologation) force us to introduce it. This will probably happen with model year 2017. But if we had to do it next year, we would be ready. But we want to keep it back and do some more testing. "

OSSA - Historic brand OSSA introduced the prototype Enduro 250i and 300i models in 2012 which featured a two stroke powerplant with a semi-reversed cylinder head and a dual fuel injector setup, with one on the crankcase and one in the head and some of these items are found on the models you can buy today. No production of the Enduro models been announced as of the time of the writing of this article.

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But that’s not a lot.

Newer two-stroke technology is still out there on the showroom floor in the applications that can support it like boats and sleds, as PWC’s have effectively made the switch.

Prototype technology in off-road models from manufacturers like KTM/Husqvarna and niche brands like OSSA may keep the hope alive for a while longer, but two-strokes have a lot of catching up to do in the off-road arena.

To be viable alternatives to cleaner burning four-strokes, not to mention the coming wave of high performance electric bikes, two-strokes off road bikes will have to radically change their game in order to survive at all. In terms of applications on our off road motorcycles, it appears that the weight and complexity of these systems, coupled with higher weights and costs, outweigh the benefits to the average consumer.

It was the EPA. Then they got rid of the open class. As 4 strokes could not compete at the 500cc level.

And 250cc 2 strokes had to compete with 450 4 strokes. 250 4 strokes with 125 2 strokes etc.

At least get the history right if your going to talk about it. Rather than making crap up. Thanks.




User Feedback




It was the EPA. Then they got rid of the open class. As 4 strokes could not compete at the 500cc level.

And 250cc 2 strokes had to compete with 450 4 strokes. 250 4 strokes with 125 2 strokes etc.

At least get the history right if your going to talk about it. Rather than making crap up. Thanks.

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    Cleaner burning is not the only or even main problem here.  We should impress upon our reader that manufacturing's impact is considerable, but so is staying involved.  All the platforms have to change to save the sport, no doubt.  We want machines that are more quiet, cleaner running, and less resource intensive to build and use (than electric especially).  Never underestimate any rider or motor.  We're on the edge of something big here...it's not about your motor - it's about having a voice and being heard.  Get out and help someone maintain a trail.  Then, you - and not your motor - will really be doing something for our sport.  Find a local club or Forest Service Unit and go spend a couple hours getting your voice out.  They WANT TO HEAR FROM US!!!    The results are almost always more miles of trail!!!

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The author makes it sound as if 2 strokes are loosing popularity. Not in my neck of the woods. Big heavy 4 strokes are being replaced by lighter easier to maneuver 2 strokes and KTM leads the way. You can't round a corner in Colorado without seeing a Big Piped orange bike. I moved down from my XCW 525 with a big bore stroker (585cc) to an XCW 300 last year. I still own the big 4 stroke but I've yet to ride anywhere where I wished I was on it in lieu of my 300. In my opinion the biggest draw to the 2 stroke is weight. After 60+ miles of technical mountain woods and trails I feel a whole lot fresher on the 2 stroke than I ever did on the 4 stroke. 

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Ummm ~ no.  The EPA had nothing to do with eliminating competition 2 strokes, they do not govern close course racing.  This is why NASCAR or any other power sport can burn thousands of gallons of high test every year with zero emission control.

 

500cc two stroke dirt bikes disappeared because sales were down, most magazines agreed that they were just too powerful (peaky compared to the current 450 4t), hard starting (if you didn't know the drill), and interest in the 500cc nationals was way down.  They were just too brutal for the average rider.

 

Letting a 450 4t compete against a 250 2t was just a way to guarantee that the 4t would win.  Don't forget that Yamaha did win a Supercross race on a prototype (but heavy) 400 4t.

 

Letting a 250f compete with a 125 2t ~ again, it was just a way to guarantee that the 4t would win.

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In slow tight single track I still have not found a thumper that won't run hot. I've yet to over heat my Berg 300 TE (same engine essentially as KTM).

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I think that if you want to compare 4stk and 2stk, you need to pick solid comparisons.  The current 350 xcf compared to a 300 xc is a good comparison.  The wet weight is not radically different, and you have to remember that you do not need to carry as much fuel on the 4stk.  I agree that a DI 2stk will not be as simple as a carburetor, I doubt it will be as far out of reach as the KTM rep made it sound.  Other than emissions, a computer controlling the mix and possibly the power valve could make tractable horsepower like the 4stk.   For out west that might not be a big deal, for anyone that has rides on slick clay or roots it is a must.

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Hey I'd just like to say I'm a fourstroke guy. I've owned two strokes (97cr250) I own a fourstroke now (03yz450f). I can honestly say I prefer the power of my fourstroke to my old two smoker. The reason you race a 450 4t against a 250 2t was because peak horsepower on a 250 2t was comparable to a 450 4t. You have more power/ combustion strokes on a 2t than a 4t at the same rpm. Get this you get twice as many. The whole 4t vs 2t is silly ride what fits you and your riding style/budget. I feel 2t are becoming popular again because of price guys can buy a cheap 2t and ride it for less than a comparable 4t. I used to trail ride my 250r it would scream places but the power delivery on my 450f is a lot easier on my arms and body at the end of the day.

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Making 2 strokes clean IS simple. AND produce even more power. It is a radical new idea...well....it was a tried and PROVEN old idea. Supercharge the inlet and don't have crankcase pumping. DKW  (inter ailia) did it in the late 40's and early fifties before the slow 4 stroke manufacturers whinged and (then) FIM banned supercharged motors thus pipping the biggest advance 2 strokes had made until expansion chambers arrived. Electric supercharging at start then crank driven would eliminate the need for oil in the fuel as the crankcase can be sealed the same as a 4 stroke. With Fuel injection ( port direct into the chamber when it's open), modern superfast ECU controlled and a variable inlet ( although reeds are probably sufficient) and variable exhaust ( power valves), two strokes would be CLEANER cc per power and torque than 4 strokes.

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im a mediocre at best... weekend warrior at the age of 40 with 3 boys.... i don't have a lot of riding experience... i had an old early 80's 2t dual sport, a 2t cr250 and a honda 450x... i loved the power delivery of the x, i loved the reliablitity of my old 2t and hated how the cr 250 scared the crap outta me every time i bleeped the throtle... i then rode a yz 125 ( don't laugh) and loved that bike... because i could ride it...  im going back to a 2t i think for one simple reason... if a 300 2t has the power delivery of modern 4t... i want one... like i said loved the x but way to hard for my skills to maintain for my style of riding i don't go through a lot of top ends on 2t

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I only ride a four stroke because I'm older and want a less radical ride. Remember the early RM and elsinores. They had a violent power band and were just old school fast. I don't know about two stroke road bikes, though I did ride a friends four cylinder kaw. two stroke and that was impressive. When I was in my twenty-ish years was always two stroke. Than into thirties went to four stroke just for some smoother slower riding.I don't follow all the epa has to say and really don't need fuel economy. Sure I care but am still at the mercy of the engineers. Just sayin...

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Good read, good comments. 

But honda had a better smoker that was cleaner, more efficient and more powerful. Google Honda R&D Chief Engineer, Yoichi Ishibashi and his INCREDIBLE accomplishments.

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Ummm ~ no.  The EPA had nothing to do with eliminating competition 2 strokes, they do not govern close course racing.  This is why NASCAR or any other power sport can burn thousands of gallons of high test every year with zero emission control.

 

500cc two stroke dirt bikes disappeared because sales were down, most magazines agreed that they were just too powerful (peaky compared to the current 450 4t), hard starting (if you didn't know the drill), and interest in the 500cc nationals was way down.  They were just too brutal for the average rider.

 

Letting a 450 4t compete against a 250 2t was just a way to guarantee that the 4t would win.  Don't forget that Yamaha did win a Supercross race on a prototype (but heavy) 400 4t.

 

Letting a 250f compete with a 125 2t ~ again, it was just a way to guarantee that the 4t would win.

no sir get your facts correct .you should do more reading . two strokes were almost eliminated because of emmisions ,, thanks

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no sir get your facts correct .you should do more reading . two strokes were almost eliminated because of emmisions ,, thanks

I am looking for a complete 500cc 2T Engine. I have built a Chopper style ride (More like a Bobber in looks) Used my old Suzuki Crystal 110cc 2T engine. Openned the exhaust, Raised Compression, found a modified (shaved and 2 spark plug) Head from Suzuki went to a 120 oversized piston and 3 rings. acutually raised ccfrom 110cc to 136cc. Used a honda NSR Carb. to solve lean condition. using 95 Octane with fuel additive or when I have at home use 9 liter 95 octane with a 2 liter AVgas (100 octane) mix. tank is 11.8 liter capacity when full for ride.

 

I want to keep 2T engine but since I built frame to use Honda, Yamaha, Suzuki or Kawasaki engines. why stop here at 136cc?? I have great low end and top end, but I get slow gain in HP @ 3100 rpm - 4650 rpm, then it pulls bigtime. If I have enough room I can usually catch whoever has tried to blast pase me while in third gear. Engine has a 4 speed semi-automatic so no clutch lever. gears have been modified to accept fullpower shifts.

 

I found that after increasing exhaust tube from 7/8" OD tubing to 1 1/8" ID actually used 150cc Suzuki exhaust. in the can I cut removeable tube 1/2" from Can end, then added another can. with one end cut off and insides removed. So I could slide it up or down untill I got the best performance welded it to original can. Again used removeable tube, this time cut it to fit flush against end of original can (about 3.5" ). This lowered the tone from a Brahhp to a Johnny Cash style Baretone Bruuhhp... Now the engine sounds more at home on this frame. I can remove this tube which leaves me a 1 1/8" hole 180 degee from original inside extended can and a semiauto shift at 4500 will pull a 3" wheelie.

 

I want to find a 500cc 2T not matter shape engine, as I can rebuild... Must be complete, If Bike is trashed, harness, complete engine, exhaust... email me:

davidstipek@msn.com

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Also I should add is the exhaust modifications cleaned 60% of the issue with emissions (lowered me 60% below the factory spec when engine was released in 1998). Engine Temp at Expansion tube and can  increased 75-80 degrees. (Before mods could grab can with hand after a good 45 minute ride, now impossible... will lift skin! Now have temp controled fan to increase air over engine, will actually cycle on/off as needed) 

 

Actually to the point that here in Thailand, there was talk if I could do it then maybe it should be required by everyone. I voiced that as long as the 2T bikes were within .75% - 1.20% of original Emissions when released from Factory. They were still legal, therefore not required to do any serious modifications to remain road worthy. Thus was agree'd.

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no sir get your facts correct .you should do more reading . two strokes were almost eliminated because of emmisions ,, thanks

Sorry buddy you're the one who needs to get your facts right. Two Stroke off road motorcycles like the yz250 and the cr125 are considered "closed course competition models" and are therefore exempt from EPA emission standards. Same goes for the yz450f and the crf250r. These are also considered "closed course competition models" and are EPA exempt. If you want to get it straight go read the CFR (Code of Federal Regulations) for this engine class and you will find that there is an exemption for competition only engines. Nice try though.

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Not the EPA, but the government. I'm not sure about today, but in the past California was the biggest market by far for off-road bikes. California has its own emissions standards for vehicle, has for years. California is the culprit in legislating the 2 stroke out of business. They introduced new laws that severely limited off-road emissions, killed the California market and the Industry responded with cleaner 4 strokes. Otherwise we'd all be riding mountain bikes.

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It's no secret Honda saw the writing on the wall that said 2-strokes were coming under fire in general, not just closed course race machines which make up a very small part of their overall business, but in all areas. 

 

There are a lot of advantages for the manufacturers to switch to the cleaner, but more complex (and more expensive) 4-stroke engines.

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Sigh.  I decide what I ride, it is my money and I choose light weight, reliability and low maintenance.  Today, KTM makes a better two-stroke dirt bike engine than Japan ever did, which makes sense, they kept up the R&D.  All of them make better low-end than any Jap two-stoke of equal displacement I ever rode.  And if you fry it?  Cheap to fix.  Fried four-strokes are absurdly expensive and complex by comparison, not to mention heavy.  If I have to hang on to the bike I have until I drop dead, then so be it.  I am not going over to four-jokes.  Valves are for toilets.

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As it is with most things mechanical, this OPOC design is not new. World War II accelerated the development of everything and this was one of the designs to come out of the effort. The OPOC design engine was used in all USN World War 2 submarines, and not one single engine failure was ever recorded. Pretty amazing record.

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The author makes it sound as if 2 strokes are loosing popularity. Not in my neck of the woods. Big heavy 4 strokes are being replaced by lighter easier to maneuver 2 strokes and KTM leads the way. You can't round a corner in Colorado without seeing a Big Piped orange bike. I moved down from my XCW 525 with a big bore stroker (585cc) to an XCW 300 last year. I still own the big 4 stroke but I've yet to ride anywhere where I wished I was on it in lieu of my 300. In my opinion the biggest draw to the 2 stroke is weight. After 60+ miles of technical mountain woods and trails I feel a whole lot fresher on the 2 stroke than I ever did on the 4 stroke. 

Yes i agree with you... I LOVED my DR650S when i had it.. That was a serious 4 stroke thumper.. BUT i do not have that 91 dino anymore.. And the more i go out the more 2 STROKES i see...As i do own 3 myself well 3 dirtbikes and now 4----- 2 stroke----3wheelers=trikes.... And everywhere i go these days EVERYONE is still rippin around on the 2 strokes around my neck of the woods in MASS

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Check out the future =) opposed piston opposed cylinder(OPOC)  http://www.ecomotors.com/opposed-piston-opposed-cylinder-engine

 

We tested one for drone designs for the government and it was amazingly lightweight and powerful.  Would be cool if they started looking into this for our favorite pastime as well.  Not sure on costs but it's cool none the less. 

 

 

twostroke-loop.gif

This is absolutely CRAZY looking.. I wonder if it really does and or would truelly work and work right and work proficiently enough to be worth it to make and test and produce and MASS produce.. Either way this lil anime... is cool nontheless

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This is absolutely CRAZY looking.. I wonder if it really does and or would truelly work and work right and work proficiently enough to be worth it to make and test and produce and MASS produce.. Either way this lil anime... is cool nontheless

Dug13 explained it above your first post "As it is with most things mechanical, this OPOC design is not new. World War II accelerated the development of everything and this was one of the designs to come out of the effort. The OPOC design engine was used in all USN World War 2 submarines, and not one single engine failure was ever recorded. Pretty amazing record."

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Also the Junkers Jumo aero engine (twin crank diesel) as fitted to the Stuka dive bomber and the Napier Deltic opposed triple crank  locomotive unit.Nothing new under the sun... Oh and Sulzer marine diesels!

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