Task: Explanation
Input (English): A desmodromic valve is a reciprocating engine valve that is positively closed by a cam and leverage system, rather than by a more conventional spring. Question: The desmodromic valve engine, widely used by Ducati, uses cams and levers to close its valves in place of what conventional mechanism? Answer: spring
Output (English): A desmodromic valve is a reciprocating engine valve that is positively closed by a cam and leverage system, rather than by a more conventional spring.