What type of metal key must the flywheel have to prevent crankshaft damage?

The correct answer is that a soft metal key is essential for the flywheel to prevent crankshaft damage. The primary purpose of the metal key is to connect the flywheel to the crankshaft while allowing for some flexibility. When the engine operates, there can be unexpected forces and stresses, especially during starts, stops, and load changes.

Soft metal keys act as a sacrificial component; they can deform or shear under excessive load or stress, thereby absorbing shock and preventing more serious damage to the crankshaft. In contrast, if a hard metal key were used, it would be less likely to deform and could transmit excessive forces directly to the crankshaft, leading to potential cracking or severe damage. Soft materials, therefore, serve as a protective measure, ensuring that the crankshaft can withstand the variances in operating conditions without sustaining permanent damage.

Choosing a soft metal key ensures that when failure occurs, it is localized to the key itself rather than affecting more critical engine components.