June 07, 2022

What are the main components of a lawn mower?

Introduction image for Main Components of a Lawn Mower.

The main components of a lawn mower include engine parts and frame parts. The lawn mower engine drives the blade (and the wheels in self-propelled models). The frame consists of the deck, wheels and handlebar.

When your lawn mower breaks down or it isn’t cutting as it should, you’ll likely need to replace one of these component parts.

Lawn mower engine parts

Carburetor

The carburetor blends air with fuel to form a combustible mixture that ignites in the cylinder to drive the engine piston. You likely need to clean or replace the carburetor when the mower starts briefly using starter fluid but won’t stay running as shown in this lawnmower DIY troubleshooting video:

To clean the engine carburetor using a carburetor rebuild kit, follow the step-by-step instructions in this article/video: How to rebuild a lawn mower carburetor.

It’s often easier (and not that much more expensive) to replace the carburetor rather than cleaning and rebuilding it. Check the price of the replacement carburetor and install a new one when the carburetor is relatively inexpensive. Follow the steps in our Replacing a Lawn Mower Carburetor video to install a new carburetor on your mower.

Air Filter

The mower's air filter removes contaminants from air before it reaches the engine, to help reduce engine wear and improve efficiency. A clogged air filter can keep air from getting to the carburetor and mixing with the gas. Replace the air filter if it’s clogged or damaged.

Spark Plug

The spark plug ignites the air and fuel mixture in the cylinder of the engine. If the engine runs rough or is hard to start, check the spark plug. Replace the spark plug if the enamel body is cracked or the electrode is fouled with carbon or other buildup. Manufacturers recommend changing the spark plug when you tune up your lawn mower. Follow the steps in our Replacing a Mower Spark Plug video to install a new spark plug in your lawn mower.

Recoil Starter

The recoil starter spins the crankshaft to start the engine when you pull the rope. Follow the troubleshooting steps in our Lawn mower won't start troubleshooting video: can't pull the recoil starter rope to fix engine starting problems when the starter rope is stuck. Replace the recoil starter if it’s damaged. Follow the step-by-step instructions in one of these 2 repair guides to replace your mower’s recoil starter depending on the type of engine that your mower has:

Ignition Coil

Located next to the flywheel, the ignition coil generates electric current to fire the spark plug when flywheel magnets spin past the ignition coil. The ignition coil sends the electric current to the spark plug at the proper time to ignite the fuel in the cylinder. A failed ignition coil is one reason a lawn mower won’t start. You can determine if the ignition coil is the problem by following the troubleshooting steps in our Lawn Mower Won't Start Troubleshooting Video: Spark and Ignition Problems.

Replace the ignition coil if it isn’t sending electric current to the spark plug. Follow the step-by-step instructions in one of these 2 repair guides to replace your mower’s ignition coil depending on the type of engine that your mower has:

Flywheel Key

The flywheel key is a small metal rectangle that keeps the crankshaft and flywheel aligned when you tighten the flywheel nut. To protect more expensive components from damage, the flywheel key is designed to shear if the mower blade hits an object hard enough to make the flywheel slip out of alignment with the crankshaft. Replace the flywheel key if you hit a rock or stump when mowing and the engine runs rough or won’t start.

Safety Switch

The safety switch stops the engine when you release the lever on the handle by stopping ignition coil current from reaching the spark plug. The safety switch also has a brake pad to slow the flywheel when you release the handle to stop the mower engine. A failed switch can prevents the ignition coil from sparking the spark plug, causing the mower to not start. Replace the safety switch if it’s damaged or broken.

Lawn mower frame parts

Mower Blade

The mower blade is a strip of metal that the motor rotates at a high speed. The sharpened side of the blade slices the grass blades to cut your lawn. Replace the mower blade when it’s dull or damaged.

Wheel

Lawn mower wheels can wear out with normal use. Fortunately, replacing a wheel is an easy repair. Follow the steps in this repair guide that shows how to replace the wheel on common Craftsman, MTD, Cub Cadet, Husqvarna, Yard-Man, Troybilt, Toro and Murray walk-behind lawn mowers: How to replace a mower wheel.

Drive Belt

The drive belt connects the engine pulley on the crankshaft to the pulley on the drive gear case. The gear case rotates the wheels to propel the mower. The mower won't move with a broken or worn drive belt. Replace the drive belt if it's worn or broken.

Transmission

The mower transmission, also called the gear case, rotates the axle to drive the wheels and move the wheels of a self-propelled mower. Replace the transmission if it's locked up or won't drive the wheels when engaged.

Drive control cable

The drive control cable connects the drive control bar to the transmission and engages the transmission to move the lawn mower when you push in the control bar. Replace the drive control cable if it’s worn or damaged.

These are the main parts of the lawn mower that most-frequently need replacing. Your mower can also experience other failures that require other part replacements. When your lawn mower breaks down, visit our DIY Lawn Mower Repair Help page to help you troubleshoot and fix problems.