BMW 11257577581 Piston

The N55 engine block is a two-piece unit made of die cast aluminum with cast iron cylinder liners and a separate bedplate. The cylinder liner features a groove between each cylinder bore, allowing coolant to flow from one side of the cooling duct to the other. The engine also features a lightweight crankshaft made of cast iron, which is approximately 3 kg (6.6 lbs) lighter than the crankshaft in the N54 engine and is counterweighted asymmetrically. The N55 engine uses KS pistons with a diameter of 82.5 mm (3.25 in). A plain rectangular ring is used for compression. The second piston ring is a taper-faced Napier ring. The oil scrape ring is a steel band ring with spring, also known as the VF system.