Which component and cover serve as the main supports for the crankshaft?

The engine cylinder assembly serves as the main support for the crankshaft in a four-stroke engine. This assembly incorporates the cylinder block, which houses the crankshaft and provides the necessary alignment and stability for its functions. Within the engine cylinder assembly, the crankshaft is mounted on main bearings that allow for smooth rotation and proper sealing, ensuring efficient engine performance.

The cylinder walls also contribute to the overall strength and rigidity of the engine structure, which is vital for maintaining the crankshaft's position and minimizing vibrations during operation. In addition, the assembly facilitates the transfer of force from the combustion process into rotational motion, making the crankshaft an essential component in the engine's power delivery system.

Other components listed, such as the cylinder head and oil seals, have specific roles in the engine but do not serve as the primary support for the crankshaft. The flywheel, while important for energy storage and smoothing out engine motion, is not part of the structural support system for the crankshaft itself.