The state of an engine, gearbox, or bearing assembly after completing its initial run cycle. During this period, microscopic surface asperities wear down, piston rings seat against cylinder walls, and friction stabilizes. A broken in machine operates at peak efficiency and lower temperatures than a brand new assembly.
Heard on the job
Don't run the dyno at wide open throttle until the new piston rings are fully broken in.
Also heard as
- run in
Related terms
Run-in
The initial operating period of a new or rebuilt machine during which mating parts wear into a precise fit.
Piston
A sliding cylinder that moves back and forth inside a hollow tube to compress fluid or transmit force.
Bearing
A machine element that constrains relative motion to a desired direction and reduces friction between moving parts.