Which component serves as the center of rotation and support on the crankshaft?

• A. Main journals
• B. Crank throws
• C. Connecting rod journals
• D. Piston pins

Answer: (A)

Main journals form the crankshaft's axis and support. They ride in the engine block’s main bearings, carrying the crankshaft and anything attached to it, so they establish the center of rotation and keep the shaft properly aligned as it spins. The offset portions called crank throws create the turning radius for the connecting rods, enabling the conversion of piston motion to rotation, but they are not the rotation center. The rod journals are the bearing surfaces where the connecting rods attach and move with the crank, yet they don’t define the shaft’s rotation axis. Piston pins connect the piston to the connecting rod and don’t contribute to supporting or rotating the crankshaft.