A desmo engine, short for desmodromic engine, is a type of engine valve control system used in certain motorcycles, particularly those manufactured by Ducati. The desmodromic system replaces the conventional valve springs found in most engines with a mechanism that uses separate cam profiles for both opening and closing the valves. This allows precise control over the valve's movement, ensuring positive and direct valve actuation.
The desmodromic system offers several advantages for motorcycle engines:
Higher RPM potential: Desmo engines can rev higher compared to engines with conventional valve springs. The positive control over valve movement eliminates the risk of valve float, where the valves may not close quickly enough at high RPMs. This allows for increased engine performance and the ability to achieve higher power outputs.
Improved engine response: The direct control over valve opening and closing enables faster and more precise valve timing. This contributes to improved engine response, allowing for sharper throttle response and better overall performance.
Reduced power loss: In engines with conventional valve springs, energy is lost due to the spring's natural tendency to compress and expand. Desmodromic systems eliminate this energy loss by actively closing the valves. As a result, desmo engines can achieve higher efficiency and potentially produce more power.
So, why don't all motorcycles use desmo engines? There are a few reasons:
Complexity and cost: The desmodromic system requires additional components, such as extra cams and rocker arms, to achieve the direct valve control. This adds complexity to the engine design and increases manufacturing costs. Consequently, desmo engines tend to be more expensive to produce and maintain compared to engines with conventional valve systems.
Maintenance requirements: Desmo engines typically require more frequent valve adjustments compared to engines with conventional valve springs. This is because the precise control of the valve movement necessitates precise adjustments over time. The need for more frequent maintenance can be seen as a drawback for some riders.
Alternative technologies: Other types of engine valve control systems, such as variable valve timing and electronic valve control, have been developed and improved over time. These technologies aim to achieve similar benefits to desmodromic systems, such as improved performance and efficiency, without the complexity and maintenance requirements associated with desmo engines.
Ultimately, the choice of engine valve control system depends on various factors, including the manufacturer's design philosophy, target performance characteristics, cost considerations, and the intended use of the motorcycle. While desmodromic engines offer certain advantages, other technologies have emerged to provide alternative solutions for achieving high-performance motorcycle engines.