Engine internals

Piston rings

Seal combustion gas and control the oil film on cylinder walls.

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

In grooves around each piston.

How it works

Compression rings limit gas leakage; the oil-control ring meters oil while allowing the piston to slide.

Think of it as

Flexible sealing bands around a moving plunger.

Symptoms when it fails

Excessive oil use or blow-by may involve rings, but ventilation and valve seals can cause similar symptoms.

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

BMW oil-consumption diagnosis considers the whole engine before concluding that piston rings are worn.

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.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.Connecting-rod bearingLets a connecting rod rotate around its crankshaft journal.