The key mechanical difference between a two-stroke engine and a four-stroke engine is that
In a two-stroke engine, the spark plug fires every revolution, which is different from four-stroke engines. Similar to a four-stroke engine, fuel and air are mixed in the cylinder. The fuel/air mixture is compressed and pushed toward the spark plug by the piston – this is known as the compression stroke.
As the fuel/air mixture is compressed in the piston, it creates a vacuum that opens a reed valve that pulls air, fuel and oil from the carburetor. The spark plug ignites the mixture and the piston is driven down by the explosion of the spark plug.
As the piston returns to its lower position, the exhaust gases are released from the cylinder and the cycle start all over again with fresh fuel entering the chamber. This is known as the combustion stroke.
Because oil is part of the mixture that is burned in the operation of a two-stroke engine, special oils are required for two-stroke engines. The crankcase is acting to pressurize the chamber with the fuel/air mixture and the fuel is mixed with oil. Because of this mixture of fuel and oil, thinner viscosity oils are often required for two-stroke engines.
Two-stroke engines often have advantages for use in small engines; but they do have issues that make them not as effective in other engine operations. Some of the disadvantages of two-stroke engines are:
Two-stroke engines have a wide variety of uses for smaller engine applications such as smaller vehicles such as ATV’s, jet skis and lawn equipment. They can deliver a higher power-to-weight ratio that is very effective for certain equipment. If you have a two-stroke engine, make sure you check out the Castrol Oil Selector to find the right two-stroke oil for your equipment.