The first hours or cycles of a new component's life, during which the tallest asperities are worn or plastically flattened, friction and temperature drop, and the mating surfaces conform. Oil from this period carries more wear metal than normal, so many shops change or filter the first fill. Gear builders sometimes call for stepped loads or special running-in oils to avoid scuffing before the flanks have bedded.
Gearbox is fresh off the rebuild, iron will look high on the first sample because it's still running-in.
Also heard as
- break-in
- wearing-in
- bedding-in
Related terms
Asperity
One of the microscopic peaks on a machined surface that makes first contact when the film gets too thin.
Scuffing
Sudden, severe adhesive damage where the oil film fails and sliding surfaces locally weld and tear.
Oil analysis
Lab testing of in-service oil samples to judge oil condition, contamination and machine wear.
Elemental analysis
Spectrometric measurement of wear metals, contaminants and additive elements in oil, in parts per million.