The Main Components of Your Lawn Mower: And Their Common Issues, Explained

In order for you to describe symptoms, describe locations of components or other pertinent information pertaining to your lawn mower, it is imperative that you grasp the main components that make up the anatomy of your lawn mower. Furthermore, common issues related to each of these components will be discussed. This will only aid in troubleshooting, diagnosing issues, or communicating to others, information necessary, for fixing your mower.

Let's begin with the engine. The engine on a lawn mower contains a vertical crankshaft, that has a blade bolted to the bottom of it. The blade is mounted to the crankshaft via a blade adapter.

In this example, two studs protrude from the adapter and mate with two holes on the blade itself, ensuring the blade is secure. The design of both blades and adapters vary in this regard. You must ensure that the blade adapter used matches the blade in which it is supposed to be mounted to. There are universal blade adapter options available, The blade adapter will have a key way that mates to the key way slot on the crankshaft. This ensures that the blade remains in constant contact with the spinning crankshaft. Pro Tip: If your mower is exhibiting excessive vibration; this may be an indicator that the blade has come loose and is not correctly fastened to the blade adapter; Or the blade has struck a hard foreign object and as a result has become bent, or its crankshaft has become bent. For more information on how to avoid such a scenario, visit this post How to Use a Lawn Mower: Sticks and Stones May Break Your Blade!

Underside of a lawn mower deck exposing blade; adapter is behind the blade

The engine is covered by an engine cover or shroud. The engine cover is designed to protect the engine and the shroud, which is a metal cover. The shroud helps to direct the air flow created by the spinning flywheel over the cooling fins designed into the engine's cylinder head. If the engine cover bolts or screws become loose, vibration may be misdiagnosed as something more serious. Ensure that these fasteners are securely fastened. The flywheel also has cooling fins that aid in this air flow. Dirt, and grass buildup on these cooling fins can prevent this air flow resulting in the engine running hotter than is acceptable, speeding up its wear.

Plastic engine cover protecting the metal engine shroud and recoil assembly underneath

Cooling fins are designed into the flywheel

Underneath the engine cover is a recoil assembly. The recoil assembly is attached to the starter rope which engages the flywheel. The flywheel must be spun manually by the operator puling the start rope (if no electric start) to start the engine. Ensure that it retracts smoothly and that it is not bound.

The engine is mounted to the lawn mower body or deck via engine mounting bolts. Ensure that none of these mounting bolts has become broken or the deck material has become cracked. The deck is the steel or (sometimes aluminum) housing in which the engine is bolted onto, and where the cutting blade resides in. Obviously, the deck's structural integrity not only prevents potential operator injury, but also supports the extremely fast moving blade and vibrating engine. To preserve your deck review this post How to Properly Clean Your Lawn Mower Without Causing Damage It outlines the importance of keeping your deck's undercarriage clean and free of grass buildup. Failure to do so encourages corrosion and through-rot from ravaging your lawn mower's deck.

The components attached to the engine but necessary for it to run include: the carburetor, engine air filter, fuel tank, fuel line, spark plug, throttle linkage, the choke and its linkage, and the governor.

The carburetor is responsible for converting liquid fuel into a vaporized mixture of air and gas, that the engine can effectively burn. The ethanol within gasoline absorbs water and causes it to separate within the gas tank, forming layers of water that can obstruct passages and ports necessary for the lawn mower carburetor to function. A varnish forms, blocking these jets and passageways preventing your equipment from starting or running properly. Corrosion can also form in metal gas tanks.

Air filter housing

Air filter cover removed exposing foam-style filter; arrow points to fuel line

carburetor behind air filter

The engine air filter is a filter used to trap abrasives from entering the combustion chamber of your engine. If allowed to enter, these particulates damage critical internal engine surfaces by scratching critical, once smooth-finished parts. it is imperative that you inspect and service your air filter periodically. The service interval may be affected by the operating conditions, such as frequent use in dusty areas, or cutting excessively tall grass. Check out this post How's Your Engine Been Breathing Lately? Air Filters and Engine Maintenance Tips for Lawnmowers to Live By! to learn how to service your engine's air filter.

The fuel tank is responsible for housing the gasoline, and it may be equipped with a filter screen, to catch debris in the gas tank from entering the carburetor. Periodic maintenance of these screens are necessary to prevent total blockage of fuel from entering the carburetor. The fuel travels from the fuel tank, through the filter screen and into the carburetor via fuel lines. These rubber fuel lines are specially designed to handle gasoline, however they can break down internally and collapse preventing or slowing the flow of fuel.

The spark plug provides spark to fire the air fuel mixture within the cylinder of the engine. If not properly maintained such as setting the electrode gap, or periodic servicing, this electrode can become fouled due to excessive carbon build up from the by-products of combustion. Refer to this post on how to assess your spark plugs:Your Spark Plug is Telling You Something...and it Never Lies: Read Your Spark Plugs Like A Pro

The carburetor's air fuel mixture is modified via linkages from a governor, that increases or decreases engine speed depending on feedback from either a mechanical device or pneumatically controlled air vane. The governor adjusted engine speed based on the operating demands placed on the engine. If these linkages become bound, disconnected, or broken this can affect the running speed of the engine. The engine can over speed higher than it is safely designed to operate within, and catastrophic failure can occur.

The choke is a plate that aids in the start up of the engine. The choke is located within the carburetor and is closed on starting and opens when the engine is set to run. It can be thermostatically controlled or manually controlled. If the choke linkage is bound, disconnected, or broken failure to start or engine running issues may result. The carburetor may also be equipped with a primer bulb. It aids in increasing the amount of fuel in the engine at cold startup, thus "priming" the engine for starting. Ensure there are no tears to your bulb.

Depiction of primer bulb

Primer bulb attached to carburetor

Operator's viewpoint looking at blade engagement bail

The engine is engaged and disengaged by the operator via a blade brake or blade engagement bail. As outlined in another post Lawn Mower Maintenance Tips: The Ones Often Overlooked proper lubrication of these cables prevents rust and corrosion from causing them to seize, rendering your machine inoperable!

Failure to service this area may make your mower inoperable!

By referring to this breakdown of the main components of your lawn mower, and learning the common issues that relate to each of these components, you are well on your way to not only prevent potential issues, but properly diagnose or communicate to those who can, what is going on with your lawn mower.

Never the Norm!