Engine internals

Cylinder bore surface

Forms the wall the piston and rings slide against.

Drag to turn it Open in the 3D lab
Where it sits

Inside each cylinder of the engine block.

How it works

The bore may be a pressed liner or a thermally sprayed coating; its fine crosshatch holds a thin oil film.

Think of it as

A smooth, hard runway inside a tube.

Symptoms when it fails

Scoring, oil consumption or low compression can involve the bore, rings or both.

Lifespan

Usually condition-based rather than a routine replacement. Lubrication, overheating and the exact engine affect wear.

Repair cost

Internal-engine work is usually labor-intensive. Diagnosis and the engine code determine the repair scope.

The BMW angle

Several modern BMW aluminium blocks use a twin-wire-arc sprayed iron coating instead of thick liners.

Used in

BMW petrol and diesel engines; petrol-only systems are identified individually.

Sources
Same system

Engine internals

Engine blockHolds the cylinders and supports the engine’s rotating parts.Cylinder headCloses the cylinders and carries the valves that control breathing.Cylinder-head gasketSeals combustion pressure, oil and coolant between the block and head.PistonReceives combustion force and moves up and down inside a cylinder.Piston ringsSeal combustion gas and control the oil film on cylinder walls.Connecting rodTransfers piston force to the crankshaft.CrankshaftTurns the pistons’ back-and-forth motion into rotation.Crankshaft main bearingSupports the crankshaft on a controlled film of oil.