Parts of a Two Cycle Outboard

I’ve been asked to give a brief refresher course as to how a two cycle engine works. There are three main components of a two cycle engine: spark plugs, compression, and power valve system. The spark plugs ignite the combustion mixture, thus generating power in the combustion stroke. The igniting spark plugs move the pistons up and down, compressing the crankcase mixture, and opening the exhaust port so a fresh supply of fuel can be taken in.

As the piston moves down toward the spark plug, the combustion mixture is compressed, thus creating a vacuum in the crankcase. The vacuum in turn causes the reed valve to open, the combustion mixture to be drawn out, and the cycle is then started over. The power valve system closes the exhaust port during piston cycles for better low-speed engine power. Now that you have a better understanding of how a two cycle engine works, you’ll know better than to supply the engine with anything other than premium two cycle outboard oil.