Engine internals
Cylinder bore surface
Forms the wall the piston and rings slide against.
Inside each cylinder of the engine block.
The bore may be a pressed liner or a thermally sprayed coating; its fine crosshatch holds a thin oil film.
A smooth, hard runway inside a tube.
Scoring, oil consumption or low compression can involve the bore, rings or both.
Usually condition-based rather than a routine replacement. Lubrication, overheating and the exact engine affect wear.
Internal-engine work is usually labor-intensive. Diagnosis and the engine code determine the repair scope.
Several modern BMW aluminium blocks use a twin-wire-arc sprayed iron coating instead of thick liners.
BMW petrol and diesel engines; petrol-only systems are identified individually.
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