When researching or buying an ATV, you may come across the words 2-stroke and 4-stroke and wonder what they mean?
Should you avoid a 2-stroke? Are 4-stroke better? Will one work better for your needs?
These are all good questions and plenty more that I want to cover in this post.
2-Stroke Engines Explained:
A 2-stroke engine, often called a “two-stroke” or “2-cycle”, is a type of internal combustion engine that completes a power cycle in just two piston strokes, as opposed to the four strokes of the more common 4-stroke engine. Here’s a breakdown of its operation:
- Intake and Compression Stroke (First Stroke): As the piston moves up, it compresses the air-fuel mix in the cylinder. This upward movement makes a vacuum in the crankcase, causing a fresh batch of air-fuel mixture to be drawn into the crankcase through the intake port.
- Power-Stroke (Second-Stroke): Once the piston reaches the top of its stroke, the spark plug sparks the air-fuel mixture, causing an explosion. This forces the piston down, producing power. As the piston approaches the bottom of its stroke, it uncovers the exhaust hole, allowing the burnt gases to be expelled. Shortly after, the transfer port is uncovered, allowing the fresh air-fuel mixture from the crankcase to enter the cylinder, pushing out any remaining exhaust gases and preparing for the next cycle.
Pros Of 2-Stroke
- Simplicity and Weight: 2-cycles have less moving parts, making them lighter and often more compact.
- Power: They deliver power for every revolution of the crankshaft, leading to a more powerful “burst” of energy compared to 4-stroke engines, which deliver power every other revolution. Think of the engine as having more torque.
- Cost: Generally, 2-cycle engines are cheaper to build and maintain because there are less parts.
Cons Of 2-Stroke
- Fuel Efficiency: They are way less fuel-efficient than 4-stroke engines.
- Emissions: 2-cycles produce a lot more emissions, making them less environmentally friendly.
- Durability: The constant high-power bursts and lack of a dedicated lubrication system (as seen in most 4-strokes) will lead to reduced engine lifespan. 2-cycle are used in weed eaters, and those engines are treated like they’re disposable.
- Oil Mixing: Many 2-cycles require users to mix oil with the gasoline to lube engine parts, adding an extra step in the refueling process. You’ll be amazed how many people don’t mix the right ratio and shorten the ATV engine lifespan.
4-Stroke Engines Explained:
A 4-stroke engine, mostly known as a “four-stroke,” is an engine that completes its power cycle in four piston strokes. The operation of a 4-stroke engine is divided into distinct phases, each represented by a piston movement:
- Intake Stroke: As the piston moves down, an air-fuel mixture is pushed into the cylinder through the intake valve, which is open.
- Compression Stroke: The intake valve closes, and as the piston moves upward, it compresses the air-fuel mixture.
- Power Stroke: As the piston gets to the top of its stroke, the spark plug ignites the air-fuel mixture. The resulting explosion forces the piston down, producing power and what moves your 4-wheeler.
- Exhaust Stroke: After the power stroke, the exhaust valve opens. As the piston moves upward again, it expels the burnt gases from the cylinder.
Pros Of 4-Stroke
- Fuel Efficiency: 4-strokes are more fuel-efficient than 2-cycle engines due to a more controlled burning process. They tend to burn fuel more completely and waste less oil.
- Lower Emissions: 4-strokes produce fewer emissions, making them more environmentally friendly and required in many riding locations.
- Durability and Maintenance: With a dedicated oil lubrication system, 4-stroke engines often have a longer lifespan and require less frequent maintenance than 2-cycles. You still need to do the basic maintenance items, but overall, 4-stroke are more durable.
- Easy Power: They offer an easier and more predictable power output, which many riders find preferable for general use and easy riding.
Cons Of 4-Stroke
- Weight and Complexity: 4-stroke engines are heavier and more complex due to additional moving parts and systems. You tend to have more features on 4-stroke, like power steering and more, which is not much of a thing on 2-strokes.
- Power: While smoother and easier, the power-to-weight ratio will be lowered compared to 2-stroke engines, as 4-strokes produce power every other revolution of the crankshaft. Since more focus is on 4-stroke, they do have more horsepower than similar 2-stroke, but if 2-stroke were not left behind, they would be much greater today.
How To Know What You Have
If you’re not sure if an quad is a 2-stroke or 4-stroke, there are several things that can give it away, such as a dipstick.
A 2-stroke engine has an oil tank and combines the oil with the gasoline for combustion (some models require you to mix the oil directly in the gas tank), whereas a 4-stroke engine does not burn oil. Typically, a 4-stroke engine will have an oil dipstick on the engine itself, while a 2-stroke will feature a separate oil tank, resembling a smaller gas tank.
Below are other ways to tell if your machine is 2-stroke or 4-stroke.
- Owner’s Manual: If you have the owner’s manual, it will clearly state whether the engine is a 2-stroke or 4-stroke. You can even get a digital owner’s manual for most models on the manufacturer’s website.
- Decals: Sometimes, the quad may have decals or imprints on the body engine casing that indicate whether it’s a 2-stroke or 4-stroke. When many manufacturers were switching to 4-stroke, they made sure to display it loudly with decals.
- Check the VIN: You can look up the ATV’s Vehicle Identification Number (VIN) and contact your local dealer to let you know if it’s a 2-stroke or 4-stroke.
- Forums and Google: Go online and check the different forums to see if your ATV is 2-stroke or 4-stroke. Simply Google “Your ATV Model and Year” and you can find a lot of info on it.
- Exhaust Smoke: 2-stroke engines often emit a bluish smoke from the exhaust, especially during startup. This is due to the oil mixed with the fuel that gets burned during combustion.
What’s Better
A 2-stroke vs 4-stroke debate and one being better is mostly personal opinion, but generally, 4-stroke are better because you can’t get 2-stroke anymore.
Due to environmental issues, 2-stroke are being phased out because they pollute too much and waste more oil and gas. While 4-stroke tend to be bigger and have more moving parts, they’re better overall for the environment.
Since this move, most manufacturers focus on making 4-stroke better and improving them with more tech and features. If 2-stroke engines weren’t kept back, they would have been the better engine due to how they work. You can still find some 2-stroke in things like dirt bikes because of weight concerns, but they too are being phased out.
Do They Still Make Two-Strokes?
Due to strict regulations, 2-stroke ATVs are not a thing anymore to buy new, at least in the US.
You can still find some manufacturers making cheap children ATVs that are 2-strokes, but it’s rare.
It is possible for 2-stroke to make a comeback, but they would need to be improved so much that it’s just not worth it, and it’s better for manufacturers to stick to 4-strokes. We have a greater shot of electric ATVs being the standard long before the 2-stroke ever comes back.
Sum Up
Picking between a 2-stroke and a 4-stroke largely depends on individual preferences, use-case scenarios, and environmental considerations.
While 2-strokes provide better low-end power and simplicity, their environmental damage and declining availability have hurt their appeal in the current market.
On the other hand, 4-strokes have become the dominant force due to their efficiency, durability, and compliance with stricter environmental regulations.
As the world evolves, with electric models hinting at the future, understanding the nuances of 2-stroke and 4-stroke engines remains invaluable for enthusiasts and buyers alike.
Understanding the nuances of 2-stroke vs 4-stroke is important, but it’s only 4-stroke you can get today if you want new and electric ATVs are more likely to come instead of 2-stroke coming back.