What are the main journals in an engine?

The main journals in an engine refer to the round surfaces on which the crankshaft rotates. These journals are critical components of the crankshaft assembly that allow for smooth rotation and effective transfer of power from the engine. The design ensures that the crankshaft can spin freely within the engine block while minimizing friction and wear.

These journal surfaces are precisely machined to withstand significant loads and operate at high speeds, which is essential for the efficiency and longevity of the engine. Proper lubrication is typically supplied to these journals to reduce friction and heat generation, enhancing engine performance.

While other components like cylindrical shafts, connecting rods, and engine bearings play vital roles in engine operation and efficiency, the primary focus of the question is on the specific surfaces that facilitate the crankshaft's rotational motion, making the round surfaces where the crankshaft spins the correct answer.