BMW Drive Belt Idler Pulley for M57N2 - INA 11287799859Part number 11287799859 Suits BMW M57N2 X5 E70 Series *NOTE: This product is an OE BMW Product, without the BMW logo, with a considerably cheaper price tag. Referred to as a deflection pulley, 80mm diameter Your BMW's idler pulley is tucked in the front of the engine accessory rack. Most often this part is overlooked for replacement until its too late. Usually a worn idler pulley will cause the drive belt to squeak or squeal upon starting the engine.