What does the term "engine break-in" refer to?

The term "engine break-in" refers to the practice of gradually acclimating a new or rebuilt engine to its operating conditions to ensure optimal performance and longevity. During this break-in period, it is essential for the engine's components, such as piston rings, bearings, and cylinder walls, to properly seat and wear in together. This gradual acclimation helps to prevent excessive wear, reduces the likelihood of future mechanical failures, and ensures that the engine reaches its full performance potential.

This process is crucial because newly manufactured or rebuilt engine parts often have microscopic roughness that needs to be smoothed out through normal operation. Proper break-in procedures typically involve varying the engine's speed and load during the initial hours of operation. This strategy allows components to adjust to one another before subjecting them to high-stress conditions, ultimately contributing to the engine's reliability and efficiency over its lifespan.