Nelitahtinen

Nelitahtinen, Finnish for "four-stroke," is a term used in engineering and everyday language to describe engines and motors that complete a power cycle in four piston strokes: intake, compression, power, and exhaust. The term is common in Finnish technical literature, education, and product labeling, and is typically paired with the noun moottori (engine) or other devices, e.g., nelitahtinen moottori.

Four-stroke operation involves valves or ports controlled by a camshaft; in spark-ignition or diesel engines, the sequence begins with an intake stroke where the piston moves downward drawing in air (and fuel in some engines), followed by a compression stroke, then the power stroke, and finally an exhaust stroke. This layout yields smoother torque and better fuel efficiency compared with two-stroke designs and generally lower emissions, though it involves more moving parts.

History: The four-stroke engine was developed in the 19th century, culminating in the Otto cycle developed by Nikolaus Otto in the 1870s, which became the basis for most modern internal-combustion engines. In Finnish usage, nelitahtinen is contrasted with kaksitahtinen (two-stroke) engines.

Contemporary use: Nelitahtinen engines are dominant in automobiles, many motorcycles, and most lawn and garden equipment. They are preferred for efficiency and emissions, though two-stroke engines remain in some lightweight applications. The term is frequently encountered in Finnish manuals, textbooks, and consumer information.