Components of a typical small four-stroke engine used to power lawn mowers, tillers, and other equipment. A two-stroke engine has most of the same components.(click to enlarge)

1. Mixes fuel and air.
2. Compresses the mixture.
3. Adds a spark to ignite it.
4. Exhausts the resulting fumes.

These four steps make up the power cycle. A two-stroke or two-cycle engine mixes and compresses in one rotation, then ignites and exhausts during the second rotation or stroke. A four-stroke or four-cycle engine requires a full rotation for each of the four steps. Most small engines are two-stroke and larger ones, like that in your automobile, are four-stroke. Two-stroke engines aren't as powerful, but they're much cheaper to build. Small engines have one or maybe two cylinders or areas where the explosions occur.

Another important fact is how the engine is cooled. Car and other larger engines are cooled by circulating liquid through channels within them. Because small engines don't develop as much heat, they typically are cooled by the surrounding air.

Maintain a small engine:

Before each use:

1. Remove debris from the air intake screen, muffler, oil filter, and governor linkage areas with a stiff plastic-bristle brush.
2. Remove the air intake screen to clean the flywheel fins.
3. If you are working on a four-stroke engine, check the oil level and add oil as needed.

Twice a year (depending on use and manufacturer's recommendations):

1. For a four-stroke engine, change the oil. Drain the old oil into a container through the drain plug or pour it out through the filler hole and refill with new oil. (Two-stroke engines don't need this step because the oil is in the fuel.)
2. Apply a small amount of lightweight oil, lithium grease, or silicone lubricant to all exposed control cable and pivot points (clutch and throttle controls).
3. Clean or replace any air filter as needed.

Replace a recoil starter rope:

1. Disconnect the spark plug cable for safety.
2. Disengage the throttle cable from the housing and remove the housing as needed to access the starter.
3. Remove the handle from the rope, which is often held in place by a knot or retainer pin.
4. Unfasten the other end of the rope from the starter using pliers or a cutter as needed.
5. Knot the end of the replacement rope.
6. Tighten the pulley counterclockwise all the way, then back it off two turns and hold it firmly.
7. Thread the unknotted rope end through the pulley hole.
8. Thread the rope through the housing hole and pull it taut.
9. Slowly release the pulley, allowing the rope to wind around the pulley.
10. Attach the handle and reassemble as needed.
11. Reconnect the spark plug cable.

Clean a foam air filter:

1. Remove the cover and lift out the foam filter.
2. Clean dirt and grease from the housing interior with a soft cloth.
3. Wash the filter with dish detergent and hot water and rinse with clear water.
4. Allow the filter to fully dry before reinstalling.