Engine internals

Connecting rod

Transfers piston force to the crankshaft.

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

Between each piston pin and crankshaft journal.

How it works

The small end pivots at the piston and the big end rotates around a lubricated crank journal.

Think of it as

The link between a pedal and a bicycle crank.

Symptoms when it fails

Deep knocking or metal in oil demands diagnosis; running the engine can worsen damage.

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

Connecting rods must match a BMW engine’s crank geometry, piston and balancing requirements.

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.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.