Which one of the following is not a recommended break-in practice for an overhauled engine?

Running an overhauled engine at idle with no load for the first few hours is not a recommended break-in practice. The break-in period for an engine is crucial for ensuring proper seating of the piston rings, bearing surfaces, and overall component wear. During this time, the engine should experience various loads and conditions to help create the necessary wear patterns for proper operation.

When an engine runs at idle without load, it does not generate sufficient heat or stresses to properly seat the components. Insufficient temperature can lead to inadequate oil circulation, preventing the necessary lubrication and potentially allowing components to wear unevenly. Idle running may also result in a situation where the engine's components do not break in effectively, which can lead to long-term performance issues such as blow-by or increased oil consumption.

In contrast, gradually increasing engine load, varying engine speeds, and allowing the engine to reach operating temperature are all practices that encourage the optimal break-in of new and overhauled engines. These practices help in achieving the right compression, ensuring that the components work together harmoniously, and reducing the likelihood of premature wear.