Monday, March 3, 2014

Understanding Your Power Tools: How Do Two Stroke Engines Work?

Understanding how your small engine works is critical to keeping it properly maintained and in working order. Two stroke engines can be especially susceptible to malfunctions, and learning about how they work will help you understand why.

Two stroke engines are internal combustion engines. This means the combustion of fuel occurs in a chamber (in our case, a cylinder) to create force to another part of the engine (a piston). There are 5 steps that are a part of all combustion engines.

1. Intake: When both air and fuel enter the engine. In the case of a power tool, this would be oxygen and the mixture of gasoline and two-stroke engine oil that you use to fuel your power equipment.

2. Compression: When the air and fuel are compressed into a small volume. In a small engine, the piston forces the fuel and air into the cylinder creating compression.

3. Ignition: When the air and fuel are burned. This occurs by the spark plug creating a spark and igniting the fuel and oxygen.

4. Power: The ignition creates energy, and therefore, power. This pushes the piston back down, allowing it to turn the crankshaft and begins to repeat the process.

5. Exhaust: The leftover gas from the ignition of the fuel and oxygen mixture exits the engine. The process is then repeated.

Here is an illustration of how this five step process works:

You might be wondering how a two-stroke engine compares to a four-stroke engine as far as gas flow is concerned. In a two-stroke engine, the flow of gas requires a seamless flow pattern to avoid any turbulent mixing of the spent charge (combusted fuel mixture) with the new charge (fresh fuel mixture). Scavenging is critical in a two stroke engine to ensure that a fresh fuel and air mixture is used in the next cycle, as defined in the 5 step process above.

Scavenging is an essential part of having a properly running engine. When this function isn’t performed properly, exhaust fumes will combine with the fresh mixture, diluting the fresh air and gas of its combustibility and causing a poorly running engine.

The reason that this information is important for operators of two-stroke engines is because proper scavenging is more difficult to achieve in a two-stroke engine making them more prone to problems. Understanding the process will help you diagnose engine issues more easily and allow you to properly install your small engine parts.

Contact us if you have any questions about installing your new small engine replacement parts from and we will be happy to help where we can!

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