Two-stroke Engines

Announcer: Go behind the wheel and under the hood on everything automotive with High Speed Stuff from Scott: Hello listeners, and welcome to the podcast. My name is Scott Benjamin, the Auto Editor here at

Ben: And as always, I am Ben Bowlin, and I write some videos here at the same website.

Scott: Hey Ben, I have something we have to maybe kind of knock out of the way before we get started here.

Ben: Oh yes, you're right, you're right.

Scott: Yup, we've got a name change coming. The name change is gonna be happening within the next couple of weeks or so. We're not sure of the exact date it's gonna happen, but we do have a new name, and the name is Car Stuff. So watch for that change coming up in the next few weeks.

Ben: I don't think we really need a Segway because we're continuing our engine series today.

Scott: Yes, yes, yes, and this is a good one. I think a lot of people are familiar with the engines we're talking about today - The two-stroke engines, and I guess maybe this is another one where whether you know it or not, you probably have heard two-stroke engines or have seen two-stroke engines or you own maybe even a couple of these. You do know if you own one because you have to do certain things in order to keep these things running. They are not like a four-stroke engine that we are used to in our cars. It's a little bit different, but we will talk about that as we go along here, but, I don't know, where do you want to start with this thing?

Ben: Well let's start with the strokes because people will recall that when we talk about the strokes, we're talking about intake, compression, combustion and exhaust.

Scott: Perfect.

Ben: When we're talking about two strokes, we're windowing down these strokes of this.

Scott: Exactly. There's really two strokes, just as you mentioned, and the only strokes that there are is a compression stroke, and a combustion stroke. So there's this rapid fire. It's an extremely fast running engine. It's just compression, combustion, compression, combustion, back and forth, super fast, and that's one of the major differences. Now, what's weird about this is that intake and exhaust also happen, but they happen simultaneously with other actions within the compression and combustion cycles, so all of the actions are happening, they just don't have their own stroke specifically for that.

Ben: Okay, all right.

Scott: Make sense?

Ben: Yes. So when we say that the two strokes in a two-stroke engine are compression and combustion, the other missing two strokes from the four-stroke engine are also happening, they're just not happening in a sequence, they're happening at the same time.

Scott: Sort of, yeah, exactly, you're right, but there is just not a stroke designated for that part of the process.

Ben: And let's go ahead maybe and talk about where we might find of these engines, if that's cool?

Scott: Yeah, yeah, no problem.

Ben: Like leaf blowers.

Scott: Exactly yeah, see you know the type of engine we're talking about. Do you own one?

Ben: Yeah. Are you kidding? I have a yard.

Scott: Well what do you hav e? How many things do you have that have a two-stroke engine in them?

Ben: Working or interesting?

Scott: Interesting.

Ben: Okay, interesting, would count working, and just the ones I can't throw away. You're gonna laugh at me, man. I have five.

Scott: Five, really? Okay.

Ben: Two of those are weed wackers that have seen better days, that I sort of inherited from my dad because they didn't work. You know, I love to get in and tinker with especially small engines, so these are kind of running projects of mine. But yeah, a lot of the smaller yard appliances, or excuse me, yard tools that have any sort of power source will often times be two-stroke engines.

Scott: Yeah, that's right, two-stroke engines, and I've only got one that's operational right now. I had two - I had a snowblower that had this as well, but I guess the easiest way to spot them is - well you can hear them running, and they sound like a chain saw because chain saw is one of the devices that uses a two-stroke engines, and there are reasons for that, too that we'll mention in a moment, but a lot of outboard boat motors are two-stroke.

Ben: Good call, Scott.

Scott: And well, there's a list here from our website that mentions dirt bikes, mopeds, jet skis, things like that, but you know, weed wackers, weed whips, whatever you want to call them, that's the kind that I have. There are trimmers of course, leaf blowers, all types of lawn equipment uses a two-stroke engine. I found myself getting sick using my snowblower because of the exhaust that was coming back on me. It was just burning so much oil, and that's one of the bad parts about this. We'll get to advantages and disadvantages.

Ben: Yeah.

Scott: We're - I guess, maybe we should just dive right into the operation of this thing, and see how it works.

Ben: Yeah, let's do that, let's do that first, and then go into the pros and cons. Scott: All right, well I guess we can talk about the combustion stroke first, so we'll talk about the two strokes. So okay, let's just say that we'll start right where the spark plug fires, okay.

Ben: All right, that's where we are.

Scott: So the spark plug has just fired. The fuel-air-oil mix, which is another unique thing is that you mix oil with the fuel, so when you get air and fuel mix in a normal engine, I mean in a four-stroke engine, you just have fuel and air. When you have a two-stroke engine, you've got fuel, air and oil mixed together, and the reason is because there is no oil well and no oil sump, so there is no continuous source of lubrication other than the fuel that you pour into that tank. That's why it is important that you mix two-cycle oil with your gasoline all the time in a two-stroke engine. So this mix in the combustion stroke has just been compressed, and the spark plug fires, and of course, you know it drives the piston back down the way it normally would in a four-stroke engine.

Ben: Sure.

Scott: And on it's way down, it passes an opening in the cylinder wall, and the opening is the exhaust port. There is no valve for an exhaust like there would be in a four-stroke engine. There's a - it's really just a machine hole in the cylinder wall, and the piston acts as a valve in this case. It does a couple of different processes, that we'll talk about, the piston is usually a little taller than it would be in a - you know, they're small, the small engines usually, but the piston is taller because it has to block and then open the exhaust valve, and then later the intake valve as well, and those again are just milled ports in the side of the cylinder. So, the combustion just happened, the piston drives itself back down, or it's been driven down by the combustion down into the - so it makes its next rotation, passes the exhaust port, the exhaust flows out of the chamber, at the same time, there's a reed valve on the other side where the intake is, and that reed valve opens up based on the pressure within the cylinder and the crankcase, which is really filled with an air-oil-fuel mix, so the reed valve opens up, and the piston passes that - well, actually it passes that area, the reed valve opens up right when it passes. It's not connected, it's off to the side. It's a vacuum situation, that's why it opens, and it allows more of the air-fuel-oil mixture to get into the cylinder, and then it drives itself - of course the momentum carries it back up, and the whole cycle starts again. So I know it sounds complex. We've got a - it's actually really, really simple. We'v e got a really good drawing, or rather an animation, on our website.

Ben: Oh yeah, yeah, yeah.

Scott: In the article, I think it's just How Two-Stroke Engines Work.

Ben: That's the one.

Scott: It's as simple as that.

Ben: It's pretty neat. You can see - I think - Is that the one we have a sound effect on? It took me a second. There's one of our engine animations that has a sound effect for the combustion.

Scott: I didn't know that. I guess I had my volume turned down or something, but - yeah, if you watch, and this is what I do too, I love to watch these animations, and you watch what happens at different points, and you have to watch it, I'll be honest, for quite a long time to get, you know because you're slowing it down, you're saying okay, this is happening at the exact time that is happening, and if you really are carefully paying attention to this because it's a well done animation, you can really see exactly what I'm talking about, and how it does what it does. I don't know, I think that's probably a simple enough description on how these things operate.

Ben: Oh yeah, you broke it down for us. Now the question people would have would be why are these two-stroke engines often used in smaller, or excuse me, in smaller yard equipment, jet skis, and the things we've already named.

Scott: Well, for one, they're lightweight. They are also relatively easy to work on. I mean, you know that, you said you work on the ones that you have, right?

Ben: I'm gonna fix - yeah, one of those weed wackers is probably beyond my abilities. It's had its days, but I'm gonna fix one.

Scott: I don't know Ben, I think you're pretty talented, I bet you can do it.

Ben: Oh, thanks man.

Scott: The other thing is that they are very powerful for their size. Because they only have two strokes, you are getting combustion on every single time the piston approaches the top of the cylinder versus on a four-stroke engine where it's every other time, so you've got a much smaller engine that's - really, it's capable of twice the output, twice the power, but you also want to be able to hold this thing in your hands. You want to be able to lift a chain saw up to be able to saw off the branch. You want to be able to hold the weed whip longer than 10 minutes so you can finish your yard. There are a lot of reasons that it is small. The other one is that you can turn this engine in any orientation that you want, and as long as you've got a good fuel, I guess the fuel suction is working correctly, the vacuum is working correctly, you can turn it in any orientation you want, and it will still operate. That's not the case with a four-stroke engine because you know, you've got the oil that's supposed to be down in the crankcase lubricating, and that only works in a certain - you know, if the engine is in an upright position, or moderately tilted, but these you can flip right upside down, and they will still operate the exact same way.

Ben: But what are the disadvantages then because the next question would have to be well, if these things are so great, if they have such a power-to-weight ratio you know, then why don't we have them in more cars? Why don't we have them in larger applications?

Scott: Well, you know honestly, Lotus was working, or Lotus is working on a two-stroke engine right now, so there is stuff in development that - now this is gonna be a little controversial because there's a problem that we'll get to in a moment with two-stroke engines that has to do with pollution, and I don't know if - I'm sure Lotus is working on this, but they have started work on a two-stroke engine, and I think that it's gonna be tough for them to get this one to pass. I don't think it's gonna go, but you never know. I never say never on this, right, but you know, take a look around, you can find that Lotus is developing a two-stroke engine. The disadvantages, and here's the reasons why a lot of two-stroke engines- you don't see a lot of two-stroke engines in cars. You know, some of those micromini cars that we had talked about, the bubble cars, had two strokes, from a long time ago, but they -

Ben: I was gonna mention that.

Scott: Oh were ya? Yeah, a lot of times you'll see these engines surrounded by a cloud of blue smoke, it's burning oil, and there's a reason for that. It's because the mix that you put in with the gasoline, and you're burning that, well not only are you burning oil in the combustion chamber, which you wouldn't be doing in a four-stroke engine, there's a point in that cycle, and if you want the animation that I mentioned earlier, there's a point in the cycle where the piston has uncovered the exhaust valve, it's also uncovered the intake valve, and the reed valve is wide open, so you get a little bit, just a small bit, and you're talking about the time between when it passes that, and when the piston comes back up to block off one of those.

Ben: So momentary.

Scott: It's extremely momentary, but there's a point where there is kind of a free flow of oil, air and gasoline pouring through the engine, straight through it.

Ben: Straight out the exhaust.

Scott: Yeah, exactly, and you can catch it in the animation, and you can see where that point is. Again, it is really, really quick, but if you watch it, you'll see it happen. So a lot of times you'll see - Like I said, there's a lot of -

Ben: So that's pollution.

Scott: That's pollution, yeah.

Ben: That's what we're talking about.

Scott: Yeah, really, and it's going to be difficult, especially with the clean air standards that we have to meet, and the restrictions that we have, I just don't think there is any way it's gonna happen because when you are mixing this concoction that you have to put into the fuel tank -

Ben: Right, when you're mixing the gas and oil.

Scott: The ratio is about 4 ounces per gallon of gasoline. That's a typical - what you use in your home machinery. The problem with that is that when you burn that much oil along with gasoline, if you're talking about in a car, and this distance isn't that great, but for every 1000 miles you travel, which I don't know about you, but that's like a week and a half for me.

Ben: Yeah, that's not too much -Scott: For every thousand miles you travel, you would be burning a full gallon of oil in your fuel tank.

Ben: I see because the problem here is one of scale.

Scott: Yeah, exactly. You're talking about a much bigger engine that is also carrying a lot more weight. It's doing a lot more work, and you're probably using it a lot more often than you do that weed whip, likely. So yeah, you're talking about an awful lot of oil that would be burned in this process. I guess that's about it. It's really, it comes -The disadvantages come down to the pollution aspect of this thing, and they don't typically last as long because of the lack of dedicated oiling, or lubrication. So they don't typically last as long. They wear out a little faster.

Ben: And also, we have to think if we took these engines, and if did go higher up on the scale, said forget the pollution, we have that solved, we would still run into the problem of increasing the consumption of oil, which would be profound.

Scott: Oh sure, it would be astronomical when you multiply that by the number of cars, even in one city. It's really something - it's a hurdle that they would have to get past, and I don't know if it's even possible because you are just talking about outright burning oil and gasoline together in order to make this thing work, and that's just the way it operates.

Ben: Well, I guess we got that taken care of. Do you want to do some Listener Mail?

Scott: I would love to do Listener Mail.

Ben: Okay Scott, you ready?

Scott: Ready.

Ben: All right, so Keith from Marysville, Washington writes in, and he says Scott and Ben, I listen to and thoroughly enjoy the podcasts on a regular basis. I appreciate the research going into such - You know, we're okay with it basically, but recently, you did in addition podcast on the Dekotora trucks of Japan. It took me completely by surprise when you failed to mention what the term Dekotora actually means. Dekotora is actually Japanese phonetic shorthand for decoration truck, in Japanese. In phoneticized English, actually because it is a foreign term rather than Japanese, so the full one is - and I'm gonna apologize here Keith, and sorry Scott, and the internet, but I'm gonna try and pronounce this, Dekoreshyon Toraku, so Deko and Tora are the first syllables of each word. So technically he is saying we don't even need the word trucks to follow the word Dekotora because they're decoration trucks, not decoration truck trucks. Keith points out that he's not normally such a knit picker, but he has lived in Japan for many years and has seen more than his lifetime's fair share of these -He calls them carnival midways on wheels, Scott.

Scott: Awesome.

Ben: Yeah, that's pretty cool.

Scott: I would love to see these in person, but good point. So we were actually saying - every time we said Dekotora truck, we were saying decoration truck truck.

Ben: Yeah, which you know, I think is an easy mistake. That was my bad though. I'll take the fall for that one.

Scott: It is. You know, I used to do some technical writing, and I'd have to - This is, like with the modules. You hear this a lot, where it's like ECM, which means engine control module, someone would say ECM module, and that drove me crazy because it would be engine control module module. So I can understand where he is coming from, there's just that little peeve that you're saying it twice. You're doing it wrong.

Ben: But you know, we love hearing mail like this because we also want to make sure that all of our listeners are informed too. We hate to misinform people.

Scott: Yeah, yeah, keep Ben on his toes because he misinforms me all the time.

Ben: I do, I don't know why. I'm so sketchy. As always, thanks for tuning in. This is gonna wrap it up for us today. If you would like to see that animation we were talking about earlier, go ahead and search for two-stroke engines in the search bar at our website. You know, send us an E-mail if you have any ideas for an upcoming show, any questions, restaurant recommendations, I don't know, limericks, Scott what do you think?

Scott: Photos of your car.

Ben: Photos of your car.

Scott: A lot of people are sending those. Some of them are great.

Ben: Oh yeah, we should look at those in more depth. Until next time, we will see you later.

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