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

Running an engine at idle (with no load) for the first few hours after an overhaul is not a recommended break-in practice because it does not allow the engine components, such as the piston rings and cylinder walls, to properly seat against each other. During the break-in period, it is crucial to subject the engine to varying loads to create the necessary conditions for the components to wear in correctly.

When an engine runs at idle, there is insufficient load and pressure to ensure complete contact between the parts that need to wear in together. This can lead to improper sealing of the piston rings, resulting in poor performance, increased oil consumption, and potentially premature engine wear. Therefore, starting the engine under load at varying speeds and loads helps to seat components effectively, ensuring a smoother and longer-lasting operation.