How a Gas Rotary Lawn Mower Engine Works

Pull Start

• The pull start operation works like a car engine’s crankshaft. The gas rotary lawn mower has a pull rope attached to a spring-pressured starting coil. Whenever the rope is pulled, the starting coil engages the crankshaft, which eventually creates a spark from the spark plug. The pull rope is typically near the top of the lawn mower’s push handle. There may also be a starter safety switch that prevents an accidental start.

Combustion

• Combustion occurs when gas vapors, oxygen and the spark from the spark plug combine inside the engine’s combustion chamber. As the crankshaft engages the engine, it creates air pressure in the piston chamber by pushing the piston down. The piston comes up and forces the air back into the combustion chamber through the carburetor, which mixes it with fuel to create an ignitable vapor. The spark plug also fires a spark on the piston’s “up” movement, igniting the vapor and creating hot air. The hot air continues to push the pistons up and down, continuously lighting the fuel-air combination and expelling the gas through the muffler. The combustion cycle happens about 1,000 times a minute.

Operation

• As long as the combustion cycle continues, the lawn mower engine rotates the mower blade. Some mowers are built with safety switches that prevent the operating engine from engaging the blade automatically. Gas rotary lawn mower engines may also come with a throttle to control how much gas enters the chamber, or a choke to reduce air intake. These engines also require oil to reduce friction among the engine’s operating parts and to reduce heat.

Maintenance

• Regular maintenance will keep gas rotary lawn mowers operating efficiently throughout the season. Spark plugs should be replaced every season and checked regularly for corrosion or debris on the tips. Any damage or interference on the spark plug can make it difficult to start the combustion cycle. Oil levels and the oil filter should also be checked and maintained. The oil filter prevents additional debris from entering the engine so that friction reduction is maintained.