Parts of a Lawn Mower Engine – Labeled Diagram to Quiz

All 19 parts on the diagram

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Outside, cover on 11

Recoil starter Pulling the rope spins the engine to start it. A recoil spring inside winds the rope back in. Also called a rewind starter.
Starter rope The rope, or cord, ends in a handle. Hold the handle and pull.
Blower housing It covers the flywheel. It directs the air the flywheel blows over the engine's fins. Also called the shroud.
Fuel tank The fuel runs from here through the fuel line to the carburetor.
Fuel cap Take it off to fill the tank. Put it back before starting.
Air cleaner It holds the filter that cleans air going into the carburetor. Also called the air filter.
Spark plug It gives a spark gap inside the cylinder. This ignites the mixture of fuel and air.
Cylinder head The block on the end of the cylinder. The spark plug is screwed into it.
Cooling fins They give the hot cylinder more surface. So the air blown over them carries the heat away. That is what air-cooled means.
Oil filler cap Oil is added here. On some engines the cap carries a dipstick for checking the oil level.
Crankshaft On a mower engine it points straight down. The piston inside the cylinder turns it.

Under the cover 8

Flywheel It spins with the crankshaft. Its fins blow cooling air, and the magnet set in its rim passes the ignition coil.
Ignition coil It sits close to the flywheel's rim. Each time the magnet passes, it makes the pulse that fires the spark plug. Also called the armature.
Spark plug wire It carries high voltage from the ignition coil to the spark plug. Its cap pulls off the plug.
Carburetor It mixes fuel and air in the right proportion for the engine.
Choke lever The choke is used for starting when the engine is cold. Some engines have a primer bulb to press in its place.
Governor spring Part of the governor, which keeps engine speed steady as load changes.
Fuel line It carries fuel from tank to carburetor.
Muffler It carries away exhaust gases and heat and muffles the engine's noise. It gets hot.

How this list was compiled: Every name checked on 2026-09-30, a name kept only where two of these use it. (1) A small-engine maker's operator's manuals for walk-behind mower engines, full text at https://archive.org/details/manualzilla-id-7348921 and https://archive.org/details/manualsbase-id-1525 : spark plug and spark plug wire, fuel tank and cap, air cleaner, starter cord handle, rewind starter, dipstick and oil fill, muffler, choke and primer, blower housing, cylinder fins, governor springs, fuel lines, flywheel. (2) A second maker's parts catalogue for a vertical-shaft mower engine, https://archive.org/details/manualzilla-id-6011158 : recoil starter and its rope, fan cover, flywheel, ignition coil, spark plug, air cleaner, carburetor, choke lever, fuel tank, fuel cap, fuel tube, muffler, oil filler cap, cylinder head, crankshaft. (3) Mid-America Vocational Curriculum Consortium, Comprehensive Small Engine Repair (1977), ERIC ED146392, https://archive.org/details/ERIC_ED146392 : recoil spring and starter rope, blower housing or shroud that directs air to the engine fins, flywheel with magnets, coil, spark plug and spark plug wire, carburetor that mixes fuel and air, choke, governor spring, fuel line from the tank to the carburetor, muffler, oil filler cap, cylinder head, fins, crankshaft. (4) Wikipedia, text only: Small engine, Lawn mower, Ignition magneto. Licence: own work

The drawing: Drawn for this site on 2026-09-30 from plain geometry; no maker's engine, nothing traced. Licence: own work

How it works

These are the parts of a small engine as fitted to a walk-behind mower: one cylinder, cooled by air, started with a rope. The first view is the outside; the second lifts the cover off.

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Outside first, then under the cover

From the side, numbers 1 to 11 are what you can see and reach: the recoil starter and its rope, the blower housing, the fuel tank and cap, the air cleaner, the spark plug in the cylinder head, the cooling fins, the oil filler cap and the crankshaft. From above with the blower housing off, 12 to 19 are the flywheel, ignition coil, spark plug wire, carburetor, choke lever, governor spring, fuel line and muffler.

How the parts work together

Pulling the rope spins the flywheel. A magnet in its rim passes the ignition coil, which fires the spark plug. The carburetor mixes fuel from the tank with air from the air cleaner, and the exhaust leaves through the muffler.

The flywheel is also the engine's fan, and the magnet in its rim makes the spark.
No choke lever on yours? Look for a primer bulb to press instead.

Questions and answers

What are the main parts of a lawn mower engine?

On the outside: the recoil starter, blower housing, fuel tank, air cleaner, spark plug, muffler and oil filler cap. Under the blower housing: the flywheel, ignition coil, carburetor and governor. The crankshaft comes out underneath.

What does the flywheel do on a lawn mower engine?

It spins with the crankshaft. Fins on it blow cooling air over the cylinder, and a magnet in its rim passes the ignition coil to make the spark.

Are the parts of a snowblower engine the same?

A gas snow blower is driven by a small engine of the same kind, so most names carry over. Small engines are built with the crankshaft either vertical, as on a rotary mower, or horizontal, depending on the machine.

What does the governor do on a small engine?

It keeps the engine speed steady as the load changes. The speed control adjusts the governor, which then moves the carburetor's throttle.