How far apart must connecting rod journals be positioned in a four-cylinder engine?

In a four-cylinder engine, the connecting rod journals must be positioned 180º apart in order to ensure proper engine balance and operation. This configuration allows for smoother power delivery and reduces vibrations, as each cylinder's power stroke is evenly spaced in relation to the others.

When the journals are spaced 180º apart, the engine operates in a manner where two pistons reach their top dead center (TDC) positions while the other two are at bottom dead center (BDC). This setup provides a balanced firing sequence, contributing to the overall stability of the engine, enhancing performance, and providing a smoother ride by minimizing any imbalance that could lead to increased wear or inefficient power delivery.

In contrast, other angles like 90º or 120º would result in uneven firing intervals, leading to more vibrations and less efficient engine operation. Therefore, the optimal configuration is the 180º spacing, ensuring that the power output from the engine remains consistent throughout the engine cycle.