What is the transmission ratio between the crankshaft and the camshaft?
2 Answers
The transmission ratio between the crankshaft and the camshaft is 2:1. Here is the relevant introduction: Principle: In a four-stroke engine, completing one working cycle requires the crankshaft to rotate 2 turns, while the camshaft only needs to rotate one turn, allowing the intake and exhaust valves to open and close once each, assisting the engine in completing one cycle. Therefore, the transmission ratio is set to 2:1. Reason: In a four-stroke engine, the camshaft rotates once while the crankshaft rotates twice, which is determined by the working principle of the four-stroke engine. The crankshaft must rotate twice for each cylinder to perform one power stroke, meaning one working cycle of the engine is 2 turns. However, within one working cycle, the valves only need to open and close once, so for the camshaft, one working cycle of the engine corresponds to one rotation of the camshaft.
Inside the engine, the relationship between the crankshaft and camshaft is actually fixed, with a transmission ratio typically at 2:1. This means the crankshaft rotates twice for every single rotation of the camshaft. The reason lies in the engine's four-stroke cycle: intake, compression, power, and exhaust. In each cycle, the camshaft controls the valves to open and close just once, while the crankshaft must drive the pistons back and forth twice. Over my years of repairing cars, I've seen numerous cases where timing chain wear or belt slack caused ratio misalignment. Incorrect ratios can affect valve timing—mild cases lead to increased fuel consumption and reduced power, while severe cases can damage the engine. That's why inspecting timing components during routine maintenance is crucial—don’t let small issues escalate into big problems.
