Engine internals

Piston pin

Joins the piston to the small end of the connecting rod.

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

Through the piston bosses and the rod’s small end.

How it works

A hardened, polished tube lets the rod swing while carrying the full combustion load; clips or a press fit locate it.

Think of it as

The hinge pin in a door.

Symptoms when it fails

A light, rhythmic knock that changes with load can point to pin clearance but needs professional diagnosis.

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

High-revving BMW M engines use short, light pins to keep reciprocating mass down.

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.