BMW N51, N52, N54, N55 6-Cylinder Sepentine Belt Failure and Power Steering Pulley Hitting Subframe
A Serpent In My BMW/MINI?
Most BMWs from the early ’90s-on and all MINIs employ the now common, serpentine type accessory drive belt systems. In deference to the older (classic) multiple V-belt system, with each belt commonly used to drive a single engine accessory (alternator, water pump, power steering, air conditioning), the serpentine system uses a single long belt to drive multiple engine accessories. As the serpentine drive system wears, it is not uncommon to begin to hear squeaking, squealing or other belt and/or pulley related sounds, indicating replacement time is near. It is far more preferable to preventatively replace the belt and pulleys prior to failure. A failed pulley or belt will, at a minimum, put the vehicle out of commission. However, as the belt derails from the pulleys, it may cause other damage as it wraps and entwines itself around the various accessories at the front of the engine. Not only is this a mess to take care of, but it may also cost more to repair due to the incidental damages from the flailing belt.
How Do I Prevent Belt Failure?
Our common recommended interval for preventative serpentine belt and pulley replacement is 80,000 to 100,000 miles. On the late model BMW “N” family 6-cylinder engines (N51, N52, N54, N55), we recommend 60,000 mile belt and pulley replacement, or sooner, if inspection shows ANY belt or pulley wear.
The N-series engines add a bit of urgency to the belt and pulley preventative replacement idea. Unlike other BMW engines, these engines do not have a balancer wheel between the crankshaft pulley (the serpentine belt drive pulley) and the engine’s timing cover. This can allow an errant belt (one that has come apart or is being derailed by a failing pulley) to slip between the pulley and the timing cover, to the crankshaft hub and oil seal. At a minimum, the oil seal can be damaged. However, it is not uncommon for the belt to be “sucked” into the timing cover, past the oil seal, and into the timing chain. If this happens, the timing chain will derail and cause the camshafts to become “untimed”, likely causing valve to piston contact and catastrophic engine damage.
When used in the E90/91/92/93 3-series chassis, the N-series engines can experience contact between the power steering pulley and the engine sub-frame. This can damage the pulley and/or the belt, resulting in the scenarios noted above. Therefore, additional detail in belt and pulley inspection is called for on these models.
BavAuto prefers and recommends the CRP (Continental Rubber Products) replacement serpentine belts and belt/pulley replacement kits (everything you need in one box). The pulleys in the CRP replacement kits are manufactured by INA, the original BMW manufacturer.
Check out this CRP video supporting and explaining the serpentine problems on the N-series 6-cylinder engines: