Small engines are all around us, powering lawn mowers, snow blowers, chain saws, generators, motorcycles, boats, snowmobiles, and many other handy tools and toys. So knowing how small engines work and what to do when they don't will put you in good standing in the Fix-It Club.

How Does It Work?

A small engine is an internal combustion gasoline engine that produces less than 40 horsepower. To produce power, the engine:

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

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.

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.

Fix-It Tip

Some two-stroke engines need special fuel that includes lubricating oil. Four-stroke engines use separate fuel and lubricant. Follow your owner's manual suggestions for mixing fuel and lubricant for a two-stroke engine, or buy premixed fuel/lubricant.

What Can Go Wrong?

Regular maintenance can keep repairs to a minimum. A starter rope may be broken or jammed. A recoil starter spring may be weak or broken. An electric starter battery may be low, connections may be loose or corroded, or a power cord may be damaged. Air filters get clogged. Fuel can become contaminated; a fuel cap breather hole may be blocked or a fuel filter clogged. A fuel line can be clogged or damaged. A choke may become sticky. A belt may slip.