Which of the following actions is most detrimental during the break-in of an overhauled engine?

Exceeding recommended RPM limits during the break-in of an overhauled engine is particularly detrimental because the break-in period is crucial for ensuring that the engine components, especially the piston rings and cylinder walls, properly mate with each other. This process involves controlled wear that helps establish optimal contact and seal between the parts.

When RPM limits are exceeded, it can lead to excessive wear or even catastrophic failure due to the increased stresses placed on the engine components. High RPMs can cause the engine to operate beyond its designed limits, leading to overheating, oil starvation, or mechanical failure due to the components not yet being fully settled.

To achieve a proper break-in, it is essential for the engine to operate within the manufacturer's specified limits to allow for a gradual and even settling of the components. This is vital for longevity and performance, making adherence to recommended RPMs during this phase critical.