What is an Engine Stroke?
2 Answers
An engine stroke refers to an engine that completes one working cycle in two strokes. In a two-stroke engine, the crankshaft rotates once, and the engine performs work once. First stroke: The piston moves from top dead center to bottom dead center, completing two actions. The spark plug ignites, performing work—exhaust, closing the intake, and compressing the air-fuel mixture from the lower part of the piston into the crankcase, then entering the cylinder again from the upper part of the piston. Second stroke: The piston moves from bottom dead center to top dead center, completing two actions. All intake and exhaust ports are closed, compressing the air-fuel mixture. Completing one working cycle requires the piston to move through two strokes, hence the name two-stroke.
I've been repairing engines for twenty years. Simply put, stroke is the distance the piston travels in the cylinder. Take the most common four-stroke engine as an example: one complete up-and-down movement of the piston counts as one stroke, and it takes four strokes (intake, compression, power, and exhaust) to complete a full cycle. We measure this distance practically - it's the straight-line distance from the piston crown's highest point to its lowest point, which is the stroke length. This number directly affects the vehicle's power and fuel consumption. Engines with longer strokes typically have stronger low-end torque and better acceleration, making them suitable for hauling or mountain driving; short-stroke engines can rev higher and perform better at high speeds. When disassembling an engine to replace piston rings, you can calculate the actual stroke value by measuring cylinder depth with vernier calipers.
