How Dirt Bike Engines Work (Two Stroke vs. Four Stroke Dirt Bikes)

How Dirt Bike Engines Work (Two-Stroke vs. Four Stroke Dirt Bikes)

Becoming a better dirt bike rider means learning more about how your dirt bike engine works. You’ll not only benefit from such knowledge in terms of how to maintain the engine properly, but you’ll also open your mind to more ideas of how can your dirt bike riding style be better! That being said, in this article, we’re going to look more thoroughly on how dirt bike engines work and what are the differences between two-stroke engines and four-stroke engines.

To know how your dirt bike engine works, you gotta figure out first whether it’s a two-stroke engine or a four-stroke. Even though everyone knows this from the moment they buy their dirt bike, but that’s not the case with people who might have gotten a dirt bike as a present from their loved ones. It’s a strange thing to mention, but my first dirt bike was a gift from my father, so as that came up to my mind, it got me thinking, what if someone doesn’t know whether their dirt bike is two-stroke or four-stroke?

Either way, depending on what type of engine you owning, the engines can work in different ways, but surprisingly enough, the basic components of both engines are very similar due to the fact that they both are combustion engines. To be more specific, you can tell that they’re similar by the fact that they both have pistons, cylinder block and head, fuel inlets and exhaust outlets and a crankshaft. Since we brought that up, let’s also point out that the lateral movement or up and down motion that the piston makes converts into a rotary movement in the crankshaft, and that goes the same by both engines, two-strokes and four-strokes.

How Does A Dirt Bike Engine Work?

If you know how a car engine works, take that as an example when trying to understand how a dirt bike engine works. No matter how absurd it may seem, but a car engine actually works in a very similar way to how a dirt bike engine works. Mostly, this is accurate with dirt bikes that have a 4-stroke engine. Even though two-strokes may seem outdated, people still use them a lot, and that’s a good thing, I am more of a fan of two-strokes than four-strokes. What I want to say by this is that a 2-stroke dirt bike engine is not very similar to a car engine, but a 4-stroke is. Some time ago, some companies even started producing 2-stroke engine cars, but that didn’t truly seem like a big step, so they just stopped manufacturing them anymore as people weren’t buying them much.

That’s not necessarily the case in the dirt bike sport, since people and companies are still manufacturing two-stroke bikes, and the most popular company for such dirt bikes is KTM. Smaller manufacturers also produce such dirt bikes, but I am not really a fan of them. If I remember correctly, KTM announced and unveiled the world’s two-stroke fuel-injected enduro dirt bike back in 2017. That was quite surprising actually since most dirt bike manufacturers in the industry were mainly oriented towards producing 4-stroke dirt bikes. Anyhow, enough with the history class, let’s get a bit more into the specifics and see what are the featured components of a standard dirt bike engine.

Regardless of whether your dirt bike is a two-stroke or a four-stroke, they both are very similar when it comes to their components. These components include:

  • Pistons
  • A cylinder block and head
  • Exhaust outlet or ports
  • Fuel inlets or ports
  • Crankshaft

Now, if you’re interested on how dirt bike gears work, that’s another topic which you can read later, but as for the engines, the pistons move up and down inside the cylinder block, a movement which is forced by the explosions of an air-fuel mixture that starts to ignite by a spark. Wondering where that spark came from? Well, there’s a spark plug included in every bike which provides a spark when it’s needed and it is positioned at the top of the engine. It sits firmly and held securely by screws that are attached to the cylinder head, which is also screwed down onto the engine cylinder block.

To understand the process better, imagine the pistons moving up and down, what happens next is that this movement turns the crankshaft. This lateral motion energy that this piston makes allows for the crankshaft’s rotary motion. To not make it sound like deep physics, this motion energy is then transmitted along the crankshaft via the transmission through the chain to the rear of the bike.

Dirt Bike Engine Classification

As you may already know, dirt bikes are mainly classified by their size and the stroke of the engine, however, the more cc the dirt bike has doesn’t necessarily mean the bigger the dirt bike is. In fact, in most cases, that doesn’t even make a difference. What makes the difference is the size of the engine which is classified by the capacity of the cc. In the short term, the engine of a dirt bike might be bigger due to the cc capacity, but that doesn’t necessarily make the dirt bike bigger.

Now, to point out some specifics, 1,000 cc translates to one liter or else 0.22 gallon, and what you get from that is that the capacity of the cylinder matters. That capacity shows the maximum volume when the piston is in the most downward position in the cylinder block. For instance, to clarify this better, you can take as an example a 250 cc dirt bike, the cylinder capacity of that amount of cc is a quarter of one liter, remember, 1,000 cc is has a one-liter capacity cylinder!

That was the first part of the classification, what else makes the difference when you classify dirt bikes is the number of engine strokes or cycles. That’s also the main topic of the article, so there are two-strokes and four-stroke engines, and the name goes along with the cc, for example, a 250cc 2-stroke dirt bike, or a 350cc 4-stroke dirt bike. From my perspective, these are the two classification methods that are more eligible, but I have also seen serious dirt bike riders classify dirt bikes in another way. To be exact, how they’d classify is the number of cylinders and the shape of the cylinders, but in my opinion that just relates back to cars.

Two stroke dirt bikes:

Two-stroke dirt bike engines take part fully in two processes which are crucial, compression and combustion. Remember the spark plug that we mentioned above, well, the spark plug ignites when the engine fires, and it is much simpler with two-stroke dirt bikes. What also makes a difference is that if you have fewer moving parts, it makes the process more sustainably active to work on and comparably lighter in weight with four-strokes. From what I have had to deal with, I can safely conclude that two-strokes are less costly to deal with when you compare the maintenance costs of a four-stroke.

If you’re after more adrenaline, a two-stroke dirt bike would be the ideal choice for you for two main reasons: unpredictable power delivery and the joy of riding fast. But, it’s important to note that a two-stroke dirt bike will require more experience in riding, and that’s very important to know if you don’t want to take any risks or whatsoever.

If you’re a newbie what I’d recommend is to go for a dirt bike that’s made for the trail, and the perfect example for that is the KTM 25-XC. It’s a very popular dirt bike among serious riders and it has been the most ideal option for beginners for years now. The reason behind it is very simple actually, it’s easier to ride than a motocross such as the YZ25, and beginners will grow fondly of this two-stroke, especially if they’ve never ridden a dirt bike in their life before.

Advantages and Disadvantages Of A Two-Stroke Cycle Engine

Advantages:

  • Lightweight (Two-Strokes weigh significantly less than four-strokes)
  • Fewer Moving Parts (A two-stroke has 40% fewer moving parts compared to a four-stroke)
  • Cheaper (Due to the fact that there are fewer moving parts and the engine is not as sophisticated as a four-stroke engine, two-stroke have significantly lower prices)
  • Less Maintenance (Easier to clean since less moving parts will be affected by water)
  • Orientation (A two-stroke doesn’t have an oil reservoir in the crankcase which means you can lubricate it while mixing the oil with fuel, and the engine will still work in any orientation)
  • More power (Even though the size or the capacity can be the same as another four-stroke, a two-stroke engine still provides more power)

Disadvantages:

  • More fuel consumption
  • Lubrication system (As the oil is mixed with the fuel, it gets burned faster)
  • Higher Hydrocarbon emissions

Four Stroke Dirt Bikes:

The way that four-stroke dirt bike engines perform differently from two-stroke engines is that besides compression and combustion, a four-stroke also involves exhaust and intake. The term revolution is the correct word to use here, so it basically fires once every two revolutions, and that’s about it. Although, what’s important to mention is that a four-stroke requires more maintenance because it has more parts, which means more parts take place in movement.

Four-stroke motocrosses are also noisier than two-stroke motocross, and a noticeable number of serious riders prefer a two-stroke over a four-stroke for this reason alone. However, different from a motocross, a four-stroke trail bike is not as noisy as a motocross, so that’s also something you should take into consideration, because it’s not the same situation all over the place. Four-strokes have a rather predictable power which enables them to be a perfect choice for beginners and riders who are just starting out in this sport. Although, this doesn’t really explain the fact that there are some really powerful four-stroke on the market, so you have to be careful if you’re to decide between a four-stroke and a two-stroke.

In trail riding, that doesn’t truly make a difference, but if you’re considering motocross races, you should think twice when deciding whether you want to get a two-stroke or a four-stroke. Nowadays, most motocross tracks are designed for four-stroke, and despite the popular belief that people have over this case, I think of it as true. The first thing that makes a difference in these tracks is the braking engine, it’s different when handling four-strokes over jumps or in corners. The market today holds more four-stroke beginners bikes than two-stroke beginner bikes, so that should help you out when choosing on a dirt bike for you.

Advantages and Disadvantages Of A Four-Stroke Cycle Engine

Advantages:

  • Fuel-Efficient (Due to the fact that a four-stroke works with valves, no air-fuel mix goes to waste from the exhaust port.
  • Cheaper Lubrication (You don’t need to add oil as often as you would with a two-stroke because the engine is lubricated using a sump reservoir system)
  • A wide range of options (The market nowadays holds more options for four-strokes than two-strokes)

Disadvantages:

  • Expensive service (It has more moving parts which means that there are more parts to change every now and then)
  • More moving parts (It gets complicated to work on a four-stroke because there are more moving parts, so maintenance is not as easy as it seems)
  • Heavier engine (These parts also add more weight to the bike)
  • Less Power (Two-stroke engines are more powerful than four-strokes)

Differences Between Two-Stroke vs. Four-Stroke Dirt Bikes

Since we got that out of the way, I assume you now know what are the advantages and disadvantages of both 2-stroke engines and 4-stroke engines. Either way, if you’re a beginner and you haven’t really decided what dirt bike you’re getting, no matter what you choose, you’re still going to experience the adrenaline and joy of dirt bike riding.

Nonetheless, before we end, I also wanted to point out some specific facts about the differences between 2-stroke vs. 4-stroke dirt bikes, and then this article should be complete. There is a wide range of differences between them, and we’ve already covered most of them in the paragraphs below, but let’s make it more clear for those that want specifics.

  • Two-stroke engines have two-piston cycles to complete a combustion and exhaust cycle, while four-stroke engines have four-piston cycles to do that.
  • The lubrication system in a two-stroke engine is simpler, you mix the oil with the fuel but is not as efficient as a four-stroke engine that has its crankcase lubricated using a constant oil reservoir.
  • A four-stroke engine has more moving parts than a two-stroke engine, which also makes it weigh more.

I don’t think there’s anything else worth mentioning since these three are the most crucial factors that you should consider before choosing whether you want a 4-stroke or a 2-stroke. If you want my opinion, what I’d recommend is a two-stroke dirt bike, in my experience, they are more practical and they deliver the adrenaline that we’re all after. Obviously, if you’re a beginner, you might as well want to go for a four-stroke, but take in mind that as you progress and improve your riding skills more, you’re going to want to go for a two-stroke which leads to a secondary purchase.

Final Verdict

This article was all about helping you understand how dirt bike engines work, and which engine is more efficient and worthy of your choice. I hope I didn’t leave any question unanswered, but in case you still have something to ask, feel free to contact me and I’ll try to get back to you as soon as possible.

As we got all that out of the table, by now you should have an idea of what makes two-stroke engines special, what makes them vulnerable, and the same for four-stroke engines. This is a very complex matter which I understand if you don’t fully get it, but at least try to remember the most important facts, such as their differences, their advantages and disadvantages.