Though there are a lot of different types and models of lawn mowers, one common characteristic most share is the type of engine used. Most mowers employ a 4 cylinder engine. In this article, we take a look at how 4 cylinder engines work. In doing so, you’ll be able to get a clear understanding of how lawn mowers work.
How a Lawn Mower Engine Works
Let’s start at the beginning. In order to start a lawn mower, the user has to hold the brake bar while simultaneously pulling the starter cord. In doing so, the flywheel starts spinning, and this is what gets the crankshaft moving. Since the crankshaft is connected to the piston, this is what gets the piston moving. So the way the process is set up the act of pulling the starter cord sets in motion the essential pieces that when combined together lead to getting the engine started.
One other vital part of the starting process is the spark plug. Its role is to create the spark that lights the gas in your mower’s engine which causes combustion. Spark plugs are powered by magnets that are attached to the flywheel. It is the spinning of the flywheel that carries the two magnets attached to it past the engine’s ignition coil that creates a magnetic field. This magnetic field is what powers the spark plug.
The 4 Stroke Process
While what was just described above is taking place outside the engine cylinder, inside the cylinder the piston is going through what’s known as a four stroke process. The first of which is the intake in which a finely tuned mixture of air and gas flows into the carburetor.
The second stroke is completed when the piston rotates to the top of the engine cylinder, closing the intake valve in the process, and trapping the air and gas that is then compressed. This is known as the compression stroke.
This is the point at which the spark plug fires, combusting the mixture of compressed air and gas, resulting in what is actually a small explosion. This explosion pushes the piston once again to the bottom of the cylinder. This is the portion of that’s called the power stroke.
The fourth and final stroke, known as the exhaust stroke, is completed when the piston is mechanically pushed back to the top of the cylinder by the spinning flywheel. As this takes place, an exhaust valve is opened to allow the exhaust that remains after combustion to leave the system. This exhaust is what goes through the muffler. At this point one cycle of the four stroke process is complete.
One of the main purposes of the crankshaft is to stabilize the pistons as they rotate back and forth. On a lawn mower, the blade responsible for cutting grass is connected to this same crankshaft which is why it spins. In essence, by keeping the pistons steady, it also performs the duty of spinning the blade that cuts the grass.
Once started an engine continues to go through the steps listed above until the process is interrupted by the user. This is done by applying the brake, which in turn closes a grounding circuit. The closing of this grounding circuit automatically applies an internal brake to the spinning flywheel. This stopping of the flywheel effectively ends the chain reaction that is causing the engine to continue running.
So that’s it. A complete explanation of how the simple and elegant 4 cycle engine, and thus your lawn mower engine works.