Manufacturers of twin-cylinder motorcycle engines have various factors to consider when deciding on the crankshaft configuration, and the choice of a 270° crankshaft is not always preferred for several reasons. Here are a few factors that influence the decision:
Engine Characteristics: The crankshaft configuration affects the firing order and engine balance, which, in turn, impacts the engine's performance, smoothness, and sound. A 270° crankshaft typically produces a firing order that creates a "V-twin" sound and can provide a slightly more irregular power delivery compared to a 180° or 360° crankshaft. However, this may not be desirable for all motorcycles or applications.
Packaging and Space Constraints: Motorcycles have limited space for engine placement and other components. A 270° crankshaft configuration can result in a wider engine compared to other configurations, which might be a limitation for certain motorcycle designs. Packaging constraints and the overall design philosophy of the motorcycle may influence the choice of crankshaft configuration.
Vibration and Balance: While a 270° crankshaft can offer improved primary balance compared to a 180° crankshaft (which can reduce vibration), it may still produce some secondary vibrations. Manufacturers need to consider the overall balance and vibration characteristics they aim for in a particular motorcycle model. Some motorcycles may prioritize smoothness, while others may prioritize a specific character or feel.
Cost and Manufacturing Considerations: The design and manufacture of engine components, including the crankshaft, can have cost implications. Depending on the specific manufacturing processes and technologies employed by a manufacturer, certain crankshaft configurations may be more feasible or cost-effective than others.
It's important to note that the choice of crankshaft configuration is a design decision made by motorcycle manufacturers, and they consider a wide range of factors, including performance goals, target market, desired sound and feel, manufacturing capabilities, and cost constraints. Different crankshaft configurations, such as 180°, 270°, or 360°, can offer distinct characteristics, and manufacturers choose the one that aligns with their overall design objectives for a particular motorcycle model.