What is the difference between a pushrod engine and a chain-driven engine in motorcycles?
2 Answers
Motorcycle pushrod engines and chain-driven engines differ only in the structure of their valve trains, and there is no inherent relationship with torque levels. Below are the relevant introductions: Chain-driven engine structure: Structurally speaking, chain-driven engines are more advanced. Chain-driven engines can increase power by raising the engine speed under the same displacement. They are compact, lightweight, have lower mechanical loads, precise ignition timing, and can integrate many advanced technologies. Therefore, high-performance, large-displacement sports bikes mostly use chain-driven engines, but they also demand higher manufacturing technology. Pushrod engine structure: Pushrod engines themselves are not suitable for high-speed operation, so they play to their strengths by typically designing the cylinder with a small bore and long stroke. This increases torque and avoids the drawbacks of high-speed operation. At medium to low speeds (commonly used range), they provide strong torque, powerful acceleration, excellent climbing performance, and good practicality.
The main difference between pushrod engines and chain-driven engines lies in their internal working mechanisms. Pushrod engines, also known as OHV (Overhead Valve) engines, rely on a camshaft located at the lower part of the engine to push rods, which then actuate the opening and closing of valves. Their structure somewhat resembles that of old-fashioned tractors—simple and reliable but with more noticeable vibrations, making them suitable for low-speed riding. On the other hand, chain-driven engines have the camshaft positioned at the top of the cylinder and use a chain for actuation, offering higher precision and a higher RPM limit, resulting in quieter operation. However, they require more frequent chain replacements for maintenance. Riding a pushrod engine, you can distinctly feel stronger vibrations, especially in congested city traffic where your hands might go numb; chain-driven engines, in contrast, provide a much smoother ride, making high-speed cruising effortless. Additionally, if the chain becomes loose or wears out, repairs can be a bit troublesome; pushrod engines, with fewer parts, are easier to fix when maintenance is needed. Maintenance costs are higher for chain-driven engines—replacing a set of chains can cost several hundred yuan—while pushrods for pushrod engines are cheaper. Engine design has evolved over decades, with pushrod engines commonly found in off-road or low-end vehicles, whereas chain-driven engines are more typical in high-performance road bikes.
