Technical reference · Doc no. ENG-04 · Rev. A four-stroke cycle

How a four-stroke engine works.

A petrol engine turns burning fuel into a spinning shaft through one repeating four-stroke cycle — Intake, Compression, Power, Exhaust — that takes two full turns of the crankshaft. The piston slides, the connecting rod converts that straight push into rotation, and the valves and spark are timed to the crank angle. Watch all three views move together.

Method: state machine + crank-slider + P–V · Not to scale

Sparkplug Intakevalve · open in Exhaustvalve · open ex Piston Conn. rod Crankshaft The cycle · 720° crank Intake Compress Power Exhaust Pressure vs. volume · idealized Otto cycle P V TDC BDC
INTAKE The intake valve opens and the descending piston draws a fuel–air mixture into the cylinder.
θ 0° · stroke 1/4

Drag the figure left/right to crank it by hand. Spark fires at the top of compression; only the power stroke does work.

FIG. 1 Four-stroke cycle. One crank angle drives three linked views — the engine cross-section, the 720° cycle ring, and the idealized Otto P–V plot. Distinct part hues are the documented multi-part exception; everything else is ink, two accents, and monospace chrome.