2st

2st is an abbreviation used in technical and hobby contexts to denote the two-stroke cycle or two-stroke engines. It appears in manuals, parts catalogs, and discussions as a shorthand to distinguish two-stroke designs from four-stroke (often labeled 4-st).

Technical background: In a two-stroke engine, a complete power cycle occurs in two piston strokes, typically one crankshaft revolution. Fresh air-fuel mixture enters the cylinder through ports as the piston rises, and exhaust exits as the piston moves. Lubrication is commonly achieved by premixing oil with fuel or by oil injection; many designs use crankcase scavenging with simple porting. The design generally yields a higher power-to-weight ratio and a simpler construction compared with four-stroke engines, but at the cost of lower fuel efficiency, higher emissions, and potentially faster wear.

Applications: Two-stroke engines have been widely used in motorcycles, mopeds, chainsaws, leaf blowers, outboard motors, and various model equipment. In recent decades, stricter emissions standards have driven technological improvements such as catalytic aftertreatment and direct injection, but 2st configurations remain common in light, portable, and performance-oriented devices where compactness and weight are priorities.

History and terminology: The practical two-stroke engine emerged in the 19th century, with early progress by inventors such as Dugald Clerk in the 1880s and later refinements by multiple engineers. The abbreviation 2-st or 2st is common in technical drawings and informal literature to indicate two-stroke configurations, especially when contrasted with 4-st (four-stroke).