Why is it important to do rod bearings?
For years BMW has been designing their engines with the goals of producing the most horsepower while also maintaining good fuel mileage for emissions purposes. Somewhere along the design phase BMW dropped the ball on some of the fundamental components of these high horsepower engines.
Engines such as the S65 and S85 were designed with less than industry standard oil clearance. In some cases this choice in clearance can be useful for efficient power but are normally compensated by using a thinner style oil for the tighter spaces.
Engines with small oil clearance along with oil that is too thick can lead to metal-to-metal contact of the bearings to rod journal creating intense heat. This heat can lead to the break down of the metal bearing coating and can lead to the bearing seizing onto the crankshaft or even spin out of place inside of the engine causing catastrophic engine failure.
