The N51 and N52 engines are in-line 6-cylinder gas motors used in several popular BMW models.
These engines use aluminum motor mount brackets as well as aluminum bolts to secure the engine to the motor mount bracket. While these components were designed to have a service life of 8 to 10 years, we have heard numerous reports of the bolts shearing prematurely — in as few as 50,000 miles. So it’s a good idea to pre-emptively change them at or before this 50k interval.
When the bolts fail, the engine movement torques the motor mounts in a way they were never designed for. Failure can also cause the engine to drop within the engine bay, damaging the water pump and other parts of the vehicle’s cooling system.
In this episode of Inside the Brands, you’ll learn more about this issue and the Rein Automotive bolt sets and kits available to do a repair. Keep in mind that both the original bolts and replacement bolts are one time use, torque-to-yield units and should be replaced in sets. We also recommend changing the motor mounts in pairs.