What is difference between 2 stroke and 4 stroke engine

The precise 2 stroke oil ratio depends on your manufacturer’s instructions, as each engine can have varied requirements. If you put too much oil, it can generate additional carbon build-up, making it difficult to start the engine.

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2stroke / 4stroke
What’s the difference between 2-stroke and 4-stroke engines?
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News You Can Use For December 2005

Most small, hand-carried lawn and garden tools such as string trimmers and chainsaws use 2-stroke engines, while larger machines such as lawn and garden tractors use 4-stroke engines. Lawn mowers are available with either type of engine.

LSU AgCenter engineer Dr. Dick Parish explains the differences and why 2-stroke engines are more commonly used on small tools.

"Most people use the terms ‘2-cycle’ or ‘4-cycle’ to describe the two engine types," Parish says. "This common terminology, while readily understood, is incorrect."

The engineer says that every reciprocating internal combustion engine operates through a "cycle" of five functions – intake, compression, ignition, combustion and exhaust. In a 2-stroke engine, all five functions of the cycle are completed in only two strokes of the piston (or one revolution of the crankshaft). In a 4-stroke engine, the five functions require four strokes of the piston (or two revolutions of the crankshaft).

Parish says 2-stroke engines aren’t lubricated by a reservoir in the crankcase but by oil mixed with the gasoline. Much of this oil is not burned by the engine and is expelled with the exhaust gas, thus increasing emissions and smoke.

He also says the power-to-weight ratio of 2-stroke engines is higher than most 4-stroke engines, so the lighter 2-stroke engines work well in hand-carried applications such as blowers and string trimmers.

"Typically, 2-stroke engines rev up to higher speeds than 4-stroke engines, and this accounts for much of the higher power per pound," Parish says. "Also, small 2-stroke engines use intake and exhaust ports instead of valves, thus saving the weight and cost of a valve train.

Parish adds that spark plug fouling is more common on 2-stroke engines because of the oil in the fuel, meaning more frequent spark plug changes may be needed.

The engineer says 4-stroke engines are lubricated by oil in the crankcase, so oil isn’t mixed with the gasoline.

"On small engines, such as those used on lawnmowers, a tab on the bottom of the piston rod splashes oil up into the cylinder," he says. "On larger engines, such as those used on garden tractors, an oil pump distributes the oil under pressure and through an oil filter."

Parish cautions that different engine manufacturers recommend different oil mix ratios for their engines.

"If you have more than one 2-stroke engine and they aren’t the same brand, you may need to keep separate fuel-to-oil mixes for the machines," he says. Typical ratios range from 32 to 1 (gasoline to oil) to 50 to 1.

"You can buy small containers of oil that are measured to provide the right amount of oil for a gallon of gasoline for a given recommended mix ratio," Parish says. "But buying oil in larger quantities may be more economical."

Another concern Parish cautions about is having trouble finding a small container measured for the ratio you require unless you go back to the dealer. Most hardware stores, garden centers, discount stores and similar stores carry only one or two ratios.

"Don’t just assume that the small container of 2-cycle oil you pick up at the discount store will give the right ratio for your engine," Parish warns. "Check the ratio on the label. It’s helpful to know how much oil you need for your required ratio in case you don’t have the correct measured container."

Parish recommends starting with a clean, empty container and pouring in the correct amount of oil. Next, add 1 gallon of gasoline, close the container and shake it to mix the fuel. Agitate the container before pouring each time you use the gasoline mix.

"Either type of engine can do a good job if used in an appropriate application," Parish says. "If you have a 2-stroke engine, be sure to mix the oil and gas correctly."

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Contact: Dick Parish at (985) 543-4125 or
Editor: Rick Bogren at (225) 578-5839 or

2stroke / 4stroke

Revs Your Heart – Explore the world of Yamaha motorcycles

What’s the difference between 2-stroke and 4-stroke engines?

Fuel for a 2-stroke engine has a small amount of oil mixed into it. It is called a “2-stroke” because just one up and down movement of the piston—the 2 strokes—performs the full cycle of intake, compression, combustion and exhaust. No intake or exhaust valves are used and instead, small holes called scavenging ports in the cylinder wall are used for drawing in air and expelling exhaust. Because combustion takes place with each revolution of the crankshaft with a 2-stroke, this format puts out more power than a 4-stroke engine and the power has more instantaneous delivery. This are some reasons why 2-stroke engines have a long history of use on many different types of motorcycles.
However, concern for more environmentally friendly performance grew and 4-stroke engines are now the norm because they inherently have better fuel economy and less exhaust smoke. As of 2019, the only 2-stroke motorcycles Yamaha makes are for closed-course competition and some models for export. Nonetheless, Yamaha 2-stroke products have a simple, lightweight construction and comparatively easy maintenance, and their high reliability keeps them popular in many regions. Today, Yamaha 2-stroke snowmobiles are used to traverse the icy cold environment of Russia, and our 2-stroke outboard engines are widely used across Africa for fishery. And, many motorcycle enthusiasts continue to love 2-strokes for their punchy, breathtaking feeling of acceleration.
As for 4-stroke engines, they run on gasoline without any oil mixed in and the piston goes up and down two times for every combustion cycle, hence it’s called a “4-stroke.” However, 4-stroke engines require valves for both the intake and exhaust that must operate with high precision, making this engine format more complex, heavier and other disadvantages. But they provide stable power delivery, good fuel efficiency, cleaner emissions and more. This is why almost all two-wheelers, from big motorcycles to small scooters, use 4-stroke engines.