Small engine

A small engine is the general term for a wide range of small-displacement, low-powered internal combustion engines used to power lawn mowers, generators, concrete mixers and many other machines that require independent power sources. Most small engines are single-cylinder, with a few V-twin units. Although much less common, there have been small Wankel (rotary) engines manufactured for use on lawn mowers and other such equipment.

Small engines are also used for wide ranges of low-displacement motor vehicles, mainly motorcycles, scooters, ATVs, and go-karts.

The engines, which may be of two or four-stroke design, are small in both physical dimensions and power output, relative to larger automobile engines. Power output ranges from less than 1 to about 15 horsepower. The smallest of all are used in handheld garden machinery, such as string trimmers and chainsaws, which may be as small as 25 cc (2 cu in) piston displacement. The most common are four-stroke air-cooled single-cylinder engines running on either petrol or diesel.

Engines for small machinery that must be hand-carried, such as string trimmers and chainsaws, are usually a two-stroke design, which is lighter for any given power output. However, two-stroke engines create a relatively large amount of air pollution and noise pollution, and so are beginning to be supplanted by four-stroke units.

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