A 4-stroke engine is a type of small internal combustion engine that uses four different piston strokes to complete one operating cycle. During this cycle, the crankshaft rotates twice while the piston goes up and down twice to fire the spark plug.


What Is a 4-Stroke Engine?

As mentioned above, a 4-stroke engine uses four separate piston events — completed up and down cycles — to achieve one power cycle. They have a slightly more complex design than 2-stroke engines that includes a compartment for oil, meaning you won’t have to premix any fuel. This feature contributes to cleaner emissions, making 4-stroke engines the more environmentally friendly option.

Thanks to their larger design, 4-stroke diesel and petrol engines tend to be larger than 2-stroke engines and weigh more. A 4-cycle engine also has more parts, but these additional features all come with excellent advantages. They help 4-cycle engines operate at much quieter noise levels, deliver better fuel efficiency and achieve longer life spans. They also deliver higher torque levels at lower RPMs.

4-Stroke Engine Parts List

The parts of a 4-stroke small engine include:

  • Piston
  • Crankshaft
  • Camshaft
  • Spark plug
  • Cylinder
  • Valves
  • Carburetor
  • Flywheel
  • Connecting rod
  • Fuel injectors

What Are the Strokes of a 4-Cycle Engine?

Here is a breakdown of the parts and functions of a 4-stroke diesel engine.

1. Intake Stroke

Small engines get fuel and air through the carburetor. The carburetor then combines the fuel and air for combustion. During the intake stroke, the intake valve between the combustion chamber and the carburetor opens, which allows atmospheric pressure to push the fuel-air mixture into the cylinder as the piston moves downward.

2. Compression Stroke

Both the intake and exhaust valves are closed in the compression stroke. As the piston moves upward, it compresses the fuel-air mixture. The compression makes it easier for the spark plug to ignite the fuel-air mixture in the power stroke.

3. Power Stroke

Once the piston gets to the top, it is at the optimum point to ignite the fuel. The spark plug creates the high voltage needed for ignition. The heat that is created by the spark ignites the gas, which then forces the piston back down in the cylinder.

4. Exhaust Stroke

Once the piston reaches the bottom, the exhaust valve opens. As the piston moves back up, it forces the exhaust gases out of the cylinder. Once the piston reaches the top, the exhaust valve closes again. The intake valve reopens, and the 4-stroke process is repeated.

Common Applications for 4-Stroke Engines

Four-stroke engines are the most common combustion engines. They are used in a wide range of different applications across multiple industries, with the most common uses including:

  • Watercraft
  • Motorcycles
  • Automobiles and trucks
  • Riding and push lawnmowers
  • Off-road vehicles and dirt bikes

Two- and 4- cycle engines are not interchangeable. Always be sure to use 4-stroke engine components and maintenance fluids when performing 4-cycle small engine services and repairs.


Contact Prime Source Parts and Equipment Today

At Prime Source Parts and Equipment, we offer product support solutions and are dedicated to helping our customers find just the right parts. With our vast network of suppliers, we have unparalleled access to the best parts available.

If you are looking for 4-cycle small engine parts or services, contact us today. Our expert staff and technicians will help you determine exactly what solutions will work best for your needs.

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