Engine internals

Piston

Receives combustion force and moves up and down inside a cylinder.

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

Inside each combustion-engine cylinder.

How it works

The piston transfers force through its wrist pin to the connecting rod; its crown and ring grooves manage heat and sealing.

Think of it as

The plunger of a syringe pushed by expanding gas.

Symptoms when it fails

Oil consumption, noise or compression loss may involve pistons, rings or cylinder wear.

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 piston shapes are tailored to combustion and valve clearance, so matching bore size alone is insufficient.

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