Two stroke engine howto



Two-stroke engines (2 cycles) complete the cycle of taking in, compressing, burning, and exhausting gases in two strokes, and are commonly spoken of as two-cycle engines. The most common use of this type of engine is for washing machines used at points where electric current is not available and for power for light boats. They are built in sizes ranging from the fractional horse power used for washing machines and other light power uses to the multi-cylinder engines developing as much power as the smaller automobile engines.

When a charge of gasoline and air is fired in the combustion chamber the engine piston is driven downward. This has the effect of compressing the fuel mixture which was drawn into the crankcase when the piston was on the upstroke.

As the piston reaches a position near the bottom of the stroke it uncovers two ports (openings in the cylinder wall). When this occurs the burned gases are allowed to pass out of the cylinder through the exhaust port at the same time the compressed mixture in the crankcase is finding its way (through the intake port) into the combustion chamber at the other side of the cylinder. The incoming gases are directed upward by the deflector on the top of the piston so that this action tends to help scavenge or clean the cylinder of the burned gases.

An automatic valve allows the fuel mixture to enter the crankcase when the piston is moving upward, and closes when the mixture in the crankcase is being compressed by the downstroke of the piston. Both sides of the piston head are used to do work. The lower side draws in and compresses the fuel. The upper side compresses the fuel charge and receives the power developed by the explosion. There is one power impulse for each revolution of the engine.