Every new internal combustion car and truck sold in America today is equipped with a four-stroke engine, as are the vast majority of motorcycles. Today, if you hear the loud, ringing song of a two-stroke, it’s probably because your neighbor has fired up a chainsaw or the local teens are playing with their dirt bikes again (vintage dirt bikes, probably). The two-stroke engine is mostly a piece of history today, but there was a time when some of the coolest developments in engine technology were two-cycle engines. Here’s how two-stroke technology rose to power, and why it’s now largely in the dustbin of history.
History is full of different engine types and even differences within those engines, but what sets a four-stroke and a two-stroke apart is much simpler than you’d think. Some people might talk about cylinder wall ports or scavenging processes, but we can discuss two-strokes and four-strokes even more simply.
During a single full cycle, an internal combustion engine must intake the fuel/air mixture, compress it, ignite it, and allow the exhaust gases created by ignition to escape. As their names imply, a four-stroke engine achieves this with four strokes of the piston, and a two-stroke does it all with just two.
In a four-stroke engine, the piston moves down during the intake cycle (that’s stroke one), pulling in a fresh air-fuel mixture. Then, the valves close and the piston moves up (stroke two), compressing the air-fuel mixture. Once the piston reaches the top of the cylinder, a spark plug ignites the mixture, starting the combustion cycle and sending the piston back down (stroke three). Finally, the piston heads up one more time (stroke four), sending exhaust gases out of the exhaust valve. You only get power every other time the piston reaches the top of the cylinder. Four-cycle diesels work in a similar way, but ignite their fuel through high compression rather than a spark plug.
A Hit With Every Two Strokes
Two-stroke engines combine multiple cycles into the same stroke of the piston. A two-stroke engine combines intake (“scavenging”) and compression into one stroke, then ignites the charge and exhausts it on the next stroke. Unlike a four-stroke and its every-other-stroke power delivery, with a two-stroke you get combustion and thus and power every time the piston reaches the top of the cylinder. The graphics above and below are from Yamaha, a brand once famous for its two-stroke motorcycles.
Critical to this process, at least in the most basic crankcase-aspirated two-strokes, is the operation of the ports. The exhaust port is exposed during the power stroke, and the exhaust begins to exit. As the piston continues down, a fresh air-fuel charge enters the combustion chamber from the crankcase through a transfer port. This charge helps push out the remaining exhaust gases while refilling the combustion chamber.
When the piston begins its upward movement again, the transfer port closes, the exhaust port closes, and the intake port opens. The movement of the piston forces the fresh charge in from the carburetor and into the crankcase, where it will wait for the engine to fire, then to scavenge exhaust gases, and start the process over again. Here’s an animation to help visualize this:
These ports, at least in a very basic two-stroke, aren’t actuated by a valvetrain like the valves in your car. Instead, the movement of the piston is what either closes or opens the ports.
The scavenging process is also one of the two-stroke’s biggest problems. Some unburned fuel is lost during the scavenging process and is sent out through the exhaust, which is bad for the environment. As Cycle World notes, a crankcase-scavenged two-stroke like the one I described above may waste 30 percent more fuel compared to an equivalent four-stroke. The publication correctly points out that such waste would be unacceptable today. However, in decades past, it was seen as a worthwhile trade-off as two-strokes often weighed 40 percent less, had less bulk, and made more than enough power for everything from lawncare equipment to boats.
Here’s an animation of a four-stroke for reference:
Engineers have developed varying ways to increase the power and efficiency of two-stroke engines. Thus, two-stroke designs can often vary wildly. But you’ll notice that two seemingly entirely different designs will still fire each time the piston reaches the top of the cylinder.
As Yamaha correctly notes, the two-stroke engine was favored for decades because firing on every rotation meant that a two-stroke made more power than a four-stroke of the same size. At the same time, two-strokes also responded more quickly. I’ve owned a variety of two-stroke motorcycles over the past seven years, and honestly, Yamaha is actually underselling it. Two-strokes often feel so much more “alive” than an equivalent four-stroke in the same application.
So, if two-stroke engines are so great, what happened to them?
A Simpler, More Efficient Engine
Despite being a much simpler device, the two-stroke engine was actually invented after the introduction of early four-stroke engines. In 1824, French physicist Nicolas Léonard Sadi Carnot proposed the Carnot cycle, a process that education company EBSCO Information Services describes as:
The Carnot cycle is a theoretical model in thermodynamics representing an idealized four-step process that a working substance, such as gas in a piston engine, undergoes to convert heat into work. This cycle consists of two isothermal (constant temperature) and two adiabatic (no heat exchange) stages, culminating in the system returning to its original state. The Carnot cycle serves as a benchmark for the maximum efficiency of real-world heat engines, revealing that no engine operating between two thermal reservoirs can be more efficient than a Carnot engine operating between the same temperatures.
The efficiency of a Carnot engine is calculated by the temperature difference between the hot and cold reservoirs divided by the high temperature, illustrating fundamental principles of thermodynamics, including the second law, which states that entropy in a closed system tends to increase. Although the Carnot cycle is not entirely realistic when applied to real engines, as real-world engines may not achieve isothermal stages, it remains a critical concept for understanding thermodynamic efficiency and has influenced the development of various engine models, including the Rankine and Otto cycles.
Historically, the ideas behind the Carnot cycle were proposed by Nicolas Léonard Sadi Carnot in the 19th century, laying the groundwork for modern thermodynamics and the understanding of energy transfer in various systems. This concept is valuable not only in mechanical applications but also in biological systems, where energy conversion processes can be analyzed similarly.
As noted above, the Carnot cycle laid the groundwork for pioneering work on engines. Many inventors tried and failed to make practical engines out of the Carnot cycle, and the few who succeeded in making a functional engine found them to be noisy, unreliable, inefficient, and sometimes dangerous.
It would take the likes of Nikolaus August Otto in Germany to make the first practical four-stroke engine, in 1876. His name is immortalized in the Otto cycle, which is used today in engines. In 1881, only five years after Otto got his four-stroke working, Scottish inventor Sir Dugald Clerk came into the picture. From Gas Engine Magazine:
Clerk was born in Glasgow, Scotland, on March 31, 1854, the son of Donald Clerk, a machinist. He studied engineering at Anderson College in Glasgow and Yorkshire College of Science in Leeds. A brilliant engineer, he also understood thermodynamics and could calculate engine pressures, temperatures and power. During World War I he was director of engineering research for the admiralty. For this, he was knighted as Sir Dugald. He built gas engines, wrote technical books, and contributed much to the development of the 2-stroke cycle. Many regard him as the father of that engine. He passed away on Nov. 12, 1932, in Ewhurst, Surrey, England.
Clerk, who had already experimented with early engines in the years prior, came up with an idea for a more efficient engine. What if an engine fired on every revolution of the crankshaft? Add in some higher compression figures, and you could achieve much greater efficiency than the other early engines of the late 1800s.
Reportedly, Clerk was a fan of American inventor George Brayton’s “Ready Motor” (above), which was pitched as being better than a steam engine because it could be started immediately without a boiler. The Brayton engine had two cylinders: one was an air pump, and the other was for combustion. Instead of a spark or some other form of intermittent ignition, a pilot flame burned constantly to ignite the fuel/air mixture.
Clerk copied this basic design, but added compression and swapped the pilot light for a spark. Then, he took the idea further. Clerk’s two-stroke engine, as we know it today, utilized two separate cylinders: One piston drew in an air-fuel mixture through a valve, and then sent the mixture out to the second cylinder. When the second piston hit top dead center, the fuel was compressed, and a spark ignited it. Then, this piston pushed down, evacuated the exhaust, and started the process all over again. It was clunky compared to modern engines, but the patented design earned Clerk the title of the father of the two-stroke engine.
The Genesis Of The Modern Two-Stroke
The invention of the more modern two-stroke engine is often credited to British engineer and inventor Joseph Henry Day. Day slapped his name on so many projects, from the cranes built by his Victoria Iron Works to his bread-making machines and even oil speculation. He’s known for inventing impressive devices, only to end up broke after getting chewed up by the market. Yet, his most influential invention was an engine, from Gas Engine Magazine:
“It seemed to me that all gas engines as then made were unnecessarily complicated, and therefore expensive to produce, and that the only chance of cutting into the engine market was to devise something very much simpler,” Day wrote.
So Day designed a two-port, 2-stroke cycle engine using just one automatic valve. The engine required an enclosed crankcase, with a poppet valve on the side that was drawn open when the piston went up. As the piston went down, it uncovered openings or “ports” in the cylinder wall that allowed the charge to be transferred from the crankcase to the power end of the cylinder. Wonderfully simple. He obtained a British patent for his design on April 14, 1891, and an American patent on Aug. 6, 1895.
This design was light and versatile; and it produced power on every revolution of the crankshaft. One of the first American firms to license the engine was the Palmer Brothers Engine Co. of Cos Cob, Connecticut (Photo 9), who quickly realized that with its excellent power-to-weight ratio it would make a perfect engine for small boats. Indeed it did, and still does today, as many “2-strokers” adhere to this identical design. If only Day knew.
What was fascinating about Day’s two-stroke engine was just how simple it was. Day’s engine achieved the same basic goal as Clerk’s, but with far less complexity. This engine would effectively serve as the distant ancestor of two-stroke engines for more than a century.
One of the most famous early two-strokes was the DKW RT-125 motorcycle. After World War II, the tooling and plans for the RT-125 went all over the world as war reparations. Suddenly, everyone from the Soviet Union to Harley-Davidson had its hands on plans for a simple German two-stroke motorcycle engine. Here in America, we got to experience the DKW RT-125 through the Harley-Davidson Hummer.
As Cycle World notes, it wasn’t long before engineers all over the world had discovered a funny limitation in the basic two-stroke motorcycle engines of the 1940s. Cylinder pressure had to be just low enough so that the cylinder would fill itself with a fresh charge when the transfer port opened. Since an early two-stroke’s ports were opened by the movement of the piston, this was achieved by having the exhaust port open sooner. Boom, cylinder pressure drops enough to begin scavenging.
However, the twist is that due to not having any real control over the port, making it open sooner also meant that it would close later than desired. So, the fresh charge would have more time to scavenge, and thus, more fresh fuel would be lost. These limitations meant that the low-displacement motorcycle two-strokes of the 1940s often made single-digit horsepower. If only there were a way to control when to open and close the ports without depending on the position of the piston.
Two-Strokes Get Complex
Engineers have come up with all kinds of wild solutions. Daniel Zimmermann, an engineer in East Germany at the time, incorporated an idea that was used in the 1920s by controlling the opening and closing of the two-stroke’s ports using a rotating disc on the crankshaft. With the rotary disc intake valve, ports can be opened and closed whenever you want them to be.
Austrian engine manufacturer Rotax had famously equipped its motorcycle engines with rotary valves, or flat discs that prevented fresh charges from going back into the intake during the compression stroke. Canada’s Can-Am’s motocross bikes of the 1970s scored countless wins thanks to the mountain of power provided by those Rotax two-strokes. It would take years for the competition to catch up.
Two-stroke power in motorcycles only became even more insane, leading to 500cc class motorcycles with torque curves that ensured power hit like a hammer, sometimes so much power that the bike could break traction at its rear tire, throwing its rider off in violent fashion.
Motorcycles didn’t get to have all of the fun. Here’s the explanation I gave for the legendary Commer TS3 two-stroke diesel engine:
In operation, a supercharger forces 6 PSI of compressed air into the intake manifold. During the compression stroke air enters one end of the cylinder with one piston while the other piston, which is slightly ahead of the other piston, closes the exhaust ports on its way in. A swirl of air is created in the cylinder as the compression stroke continues. As both pistons close on each other and the engine reaches inner dead center (this engine’s equivalent of top dead center), fuel is injected from the middle of the cylinder. The heat and pressure generated during the compression stroke ignite the fuel at about where the pistons meet, starting the power stroke.
As the pistons pull away from each other, the exhaust ports open, blowing exhaust gases out. Once the pistons reach their furthest distance apart, the intake ports open, pushing in compressed fresh air and scavenging the rest of the exhaust gases. Then, the cylinders start coming back at each other, closing the exhaust ports and starting the process all over again.
Rootes TS3 Engine Services notes that opposed-piston engines have several advantages over the typical diesel engine of the era. The Commer TS3 didn’t have cylinder heads, head gaskets, rocker cover gaskets, camshafts, valves, or pushrods to fail. Further, the engine didn’t have the ancillaries necessary to run valves, which means even fewer points of failure. It’s also noted that the TS3 was even further optimized by the fact that sure, it had six pistons, but only three cylinders. That meant fewer injectors. Finally, due to the opposed-piston design, the engine naturally provided its own equal and opposing forces, negating the need for counterbalances in the crank.
Then there’s the even crazier Napier Deltic (video above), another two-stroke diesel, which was more or less three complex two-stroke diesels combined into a single, ridiculously complicated diesel. I wrote a whole story on that one, which you can read by clicking here.
But as you can see, as two-strokes got more powerful and more intricate, so did their solutions for the problems that had been known about two-strokes for decades. The Detroit Diesel Series 71 engine family did not use the crankcase for aspiration like the early two-strokes I wrote about above. Thus, these Detroits couldn’t naturally pull in a fresh charge of air and fuel. Instead, a Roots-type blower was used for scavenging and injectors for fuel.
But forget about the 8 HP motorcycle two-stroke units of the past. Can-Am’s Rotax engines made over 60 HP, and the Detroits directly above? Series 71 engines got so hot that there was the 16V-71, an 800 HP and 2,150 lb-ft of torque V16 two-stroke diesel. Napier Deltic D18-11B 18-cylinder, 32-piston two-strokes were pumping out a continuous 1,875 HP.
Some of the coolest-sounding buses and trucks on this planet are strapped with two-strokes. Listen to this:
Two-Strokes Are Fun And Weird
My 2005 Genuine Stella, licensed copy of a Vespa PX built in India, makes only 8 HP with its 150cc two-stroke. That’s less power than you’d get out of a Honda Grom with a 125cc four-stroke engine.
Yet, because two-strokes have a different torque curve than a four-stroke, my Stella is somewhat of a wild ride. Two-strokes are generally known for narrow and peaky powerbands that aren’t as linear or wide as you get in a four-stroke. To you, the driver or rider, it’s fun because a two-stroke gives you a whole helping of power right when you hit the sweet spot.
But two-strokes also have some quirks. The simplest two-strokes, like the one found in my Vespa above and some cars, use a total-loss lubrication system where you have to mix oil into the fuel to lubricate the engine’s components. The oil is then burned off as you ride or drive. Sure, there’s no oil to “change” like in a typical car of today, but now you have to worry about getting the mix just right or whether your autolube system, if equipped, is still working.
Of course, there’s also the emissions problem of burning oil by design. Many vintage two-strokes put out visible smoke, something that looks out of place in the modern day. Two-stroke engines in cars also had a funny problem.
When you drive downhill, you may let off the throttle, coast, and let gravity do the heavy lifting. Under normal circumstances, with a manual transmission and a four-stroke engine, the engine speed may increase, but that’s not a big deal. In a two-stroke, this is bad because the engine depends on the fuel and oil flow for lubrication, so now the engine speed is increasing, but the engine is being starved of lubrication. If the downhill stretch is long enough, that could lead to engine damage or even a seizure.
Saab famously had a fix for this for its two-strokes with a freewheel. This was a giant roller clutch, and when you let off the throttle, the rollers free up, allowing the engine to safely idle while you coasted down a hill. The freewheel also allowed Saab owners to shift gears without hitting the clutch pedal. You could also lock the freewheel, keeping the engine engaged, so that you could have engine braking. This is also how common bicycles work. Check it out:
Saab didn’t invent this feature. Cord, Rover, Packard, and even Land Rover used variations of the freewheel in their designs, too.
Once Great, Now Fading Away
Sadly, I’m sure you can see why the two-stroke failed. Over a century ago, the two-stroke engine represented a way to get good power out of a very simple and lightweight design. Then, the two-stroke evolved into something complex, yet still dominating in its fields.
Unfortunately, nothing lasts forever. Four-stroke technology eventually caught up, and did so with lower emissions, better fuel economy, and arguably easier maintenance. Sure, two-strokes have also gotten advanced, today’s manufacturers look to four-strokes to meet demanding emissions and fuel economy regulations. Buyer preferences also changed. The rider of a four-stroke motorcycle could come home not smelling like exhaust smoke and four-strokes eliminate the worry about premix.
Of course, we’re also at a turning point in alternative fuels, where EVs have become mainstream. This only further drives a stake into the two-stroke. That said, two-stroke engines aren’t entirely dead. You can still buy two-stroke chainsaws and other equipment. Two-stroke dirt bikes are still a thing, too. The last time I went swimming I also heard the familiar sound of a two-stroke outboard.
However, two-strokes aren’t where they used to be. You won’t ride a new bus with a two-stroke diesel and you aren’t going to buy a new two-stroke car, either. You also won’t be buying a two-stroke road motorcycle from a mainstream brand in America, either. A lot of folks will see that as a good thing. I’m sure lots of you are fed up with hearing two-stroke lawncare equipment! But it just goes to show how two-strokes were once titans, and now they’re old news.
(Update: Clarified the function of Detroit Series 71 engines.)
Top graphic images: Saab; A. Schierwagen via Wikimedia Commons/Attribution-Share Alike 3.0 Unported licence
Do you think that they could, somehow, make a cleaner return? A supercharger here, a sealed oiling circuit there, direct injection there..? Without a valvetrain and spring valves sapping power and clever engineering, i see potential here… ????
My family had a 2-stroke lawnmower when I was a kid and it was such a hateful, noisy, smelly thing that was incredibly difficult to start. Rest in piss, Lawn Boy.
2 strokes are far from dead on the cross country racing dirt bike scene. The European marques especially have made them their specialty. See Husqvarna, Gasgas, Beta, Sherco, KTM for example (I’m sure I’m forgetting more).
Awesome deep dive! Two-strokes are alive and well in the karting world, from 50cc kid karts all the way to seniors with some of the fastest karts at the track in the 125cc TaG or shifter classes.
As far as I can tell, every single delivery rider round here has a 2-stroke moped.
Small 2 stroke outboards haven’t been sold in the US in years, but still remain in fairly high demand among sailors of small boats. It’s not uncommon for cruisers to pick up current model 2 stroke outboards when they sail abroad. I currently own 3 old tohatsu/mercury 2 strokes- a 5hp and two 3.5hps for my J/24. They’re just smaller and lighter than the equivalent 4 stroke. They don’t have to be stowed on the ‘correct’ side belowdeck due to the internal oil on 4 strokes. Yes, you need to pre-mix the oil but that’s pretty routine. I also have a number of 4 strokes from 6 to 60hp on my other boats, and they’re fine, but I always feel like I have to treat them with more respect and can’t just toss them down the hatch.
All you need to know about 2 Strokes you can find out by looking up Larry Enticer on Youtube
my understanding of why yard equipment prefers 2-stroke vs 4-stroke is that they can operate upside down.
oil-fuel mix in crankcase lubricates regardless of orientation, whilst 4-stroke not-so-much.
good article, informative and entertaining.
I love my 2 stroke Yamaha Jog, it’s an absolute blast to ride. It’s my first 2 stroke and I love the simplicity and how easy they are to work on. This may be Jog specific but I also love how cheap and easy performance upgrades are for it. I honestly don’t think I’d have any interest in a 4 stroke 50-70cc moped, they just aren’t the same.
Gordon Jennings: Two Stroke Tuners Handbook was an excellent reference back in the day. Probably still a good way to melt some aluminum if you wish to dabble.
Likely downloadable as a pdf somewhere. (-;
Fun fact, in the Eastern Bloc there were so many 2-stroke cars that gas stations sold premix fuel. Trabants, Wartburgs, Barkases and most bikes all ran on premix, they did not have autolube systems.
Some stations had an adjustable setting so you could get 1:25 or 1:33 mix from 88 or 91 octane but later 91 1:40 and 95 1:50 mixes became more prevalent.
These type of fuel dispensers completely disappeared in the early 2000s.
I rode cr250 and 500 two stroke motocross bikes for several years until I got too big to be competitive. Later on had a RD400 Yamaha two stoker. Moved up to a Suzuki GT750 water buffalo. A bunch of us had various Yamaha and Kawi two stokes and used to rat around the city being youtful idiots. One buddy had the feared kawa 750 widow maker. The guy was fearless. He later converted it over to a drag bike and stitched his street rider to a Suzuki gs 1100.
I’m conflicted. One of the highlights of my career was a 2-stroke research engine that had great emissions, but I’m also violently opposed to pistons being a service item.
I’m sure in 20 years time we’ll have EV dorks arguing about axial flux motors being slightly less bland than radial flux, or something.
Great article, as always. Now do a deep dive on the KTM fuel injected two stroke!
Like the Wankel, I love the relative simplicity of the design, but I never liked them in practice—the (awful) noise, the smell, the pollution, and the lack of torque are all things I hate and they generally came connected to machines I associate with unpleasant work or antisocial dirtbags behaving according to that label. It’s especially great to not have to hear them much anymore or see the smoke when on trails or on the water. With boats, once they had 4-stroke OBs dialed in, I don’t see why anyone would want a 2-stroke other than for the weight, but 4-strokes have gotten pretty light now. Small boating with 2-S OBs was just such a trashy experience while 4-Ss are clean, smooth, and quiet, almost like they’re not there. It’s not all clear and quiet skies, though, as there seems to be a resurgence of 2-Ss in the cities with shitty mini bikes being ridden in the typical manner I’ve always associated with 2-stroke users. Is there something inherent to 2-Ss that drives the behavior or merely that they’re cheap junk used in bottom-barrel toys that even nearly broke people can still seemingly afford/the cheapness makes them common enough that they are easily stolen? Guess there’s little hope of the EPA banning importation of this junk at this point, but maybe tariffs will do some good and price them out of the market.
The ol’ Harley Hummer. I have a ’63 Pacer that’s been in my family for ages–all my memories of it are it just gathering dust in a corner. Basically my dad and grandpa rebuilt it and then just… never used it anymore. Next year’s summer spring project, and my first attempt at working on a 2-stroke.
I don’t know if I’ll ever bring it home to the big lights and mean streets of Chicago, but it can be used to tool around the county back at the farm just fine. That’s mostly what I understand it was used for back in the day.
I only owned two motorcycles in my brief riding career that ended in 1979- but both were two stroke triples.
First one was a brand new 1978 Kawasaki KH 400, $1049 out the door. It wasn’t the Widowmaker that its 500 and 750 predecessors were but it could walk away from a Honda 550 any day every day.
They really made this machine easy to live with by using a magneto ignition and an excellent oil injection pump. It never fouled a plug! The power came on hard about 3 grand and pulled to almost 7000. I did one road trip from the Bay Area to New Mexico, and it got about 32 mpg for the trip. Sold at 11,000 and the buyer ended up restoring it to almost stock condition. He got 6 tickets in 9 months.
Selling it made room for a freshly rebuilt ’76 Suzuki GT 750. Super comfortable, pulled incredibly below 5 grand, it was a great touring bike. Mods included automotive coils and straight pull Mikuni carbs. I wrecked it near Cabo San Lucas, broke my back and that was the end of my riding days.
I miss both of them, the howl of the 400 and the grunt of the 750 made for many miles of great riding.
Water cooling of a 2 stroke bike engine was a definite step in the right direction for emissions and noise reduction. Too bad government regulations pretty much shut down continued development.
I’m a big fan of two strokes; the responsiveness is just FUN.
Example: On snowmobiles, I’ve had 2 strokes and 4 strokes of the exact same sled, with similar HP. The 4 stroke is torquier, you can feel it pull when you get the throttle going… but the 2 stroke is lighter, and more blip brapppppp responsive. When the trails get wooped out, the 4 stroke sled crashes down into each valley, and then crashes up on each rise. Meanwhile, on my 2 stroke sled, I can blip the throttle as I traverse over them, and due to less weight AND instant response, the sled shifts the weight back and forwards, so that I float right over the bumps. Think of a car doing several almost wheelies, on even terrain, if that makes sense.
They’re also super reliable now, or they were. The last sled I sold had 11,000 miles which is kind of insane, but it was also not a very clean running engine; it smokes and drinks oil and gas like a sailor. Newer sleds meet EPA requirements, but they often burn up/blow up around 5-6k miles. Why? Because they are running way leaner, the emissions are left, and to keep things lubricated, they are using sealed bearings. Meanwhile, my old Zuke 800 had regular open bearings, but since the thing was running so rich and oily, it just lasted double the miles of a modern snowmobile engine.
Is it truly greener and better for the environment if the engines last half as long? I would say not, as most people would probably just part out the sled instead of getting another engine. Even then, think of all the waste/energy required to produce even a new engine, let alone the whole sled.
Boating is much the same thing; I have fast v8s with i/os, and I have fast 2 stroke outboards. The same thing that makes them fun on a sled makes them fun on the water; they don’t weigh much and the throttle response is awesome. They run dirty and oily, so they last a very long time as long as you don’t go after bleeding edge power and start shaving heads to increase compression and whatnot.
Lastly, check out Evinrude/BRP’s eTec 2 stroke technology on outboards. They’ve been careful to remove ‘2 stroke’ from all the literature on their website… but that’s what they are! Evinrude’s eTecs were running cleaner than Mercury’s 4 strokes… but they failed, because of 2 stroke’s reputation for being dirty and smoky, even when they’re running cleaner than 4 strokes.
Werent there a bunch of quality /durability problems with the eTech? I loved my 2 stroke Yamaha outboard (150HP- 3.8gallons/hr on plane)
Nope. Seems like a good engine, marketed poorly at the wrong time.
There were problems with Yamaha outboards and their disposable flywheels that needed to be replaced every 300 hours or so