An article written by Randy Yuan.
Recently there have been many threads sprouting up on M5board regarding the E60/61 M5 and E63/64 M6 cars having worn/spun rod bearings. Some bearings show minimal signs of wear of just the lead layer being exposed, but majority show heavy wear in that the deepest layer of copper is visible. Definitely if you are down to the copper layer it is time to change out the bearings. Many of these instances actually result in the owners replacing the entire S85 engine block due to metal shavings found in the oil or in worst case engines just completely failing to operate. It seems that having an F1 inspired engine comes with F1 tolerances. BMW had released a newer rod bearing supposedly with larger tolerances to help address these issues.
Taking oil samples and sending them to Blackstone Labs for an oil analysis is one way to check on the health of your engine. For me, my past two Blackstone reports came back clean, but my car's mileage was getting to be high at 83,000 miles so I decided to take preventative measures and approached Performance Technic to have my rod bearings changed out for WPC treated ones, which are not only stronger and more durable than OEM bearings, but also have reduced friction due to the treatment. Details on the treatment can be found here (http://www.wpctreatment.com/).
Even though the newer OEM rod bearings supposedly had larger tolerances, I wanted to play it extra safe by adding the WPC treatment.
In addition,I also asked PTech to use ARP bolts as they only require one torque instead of three in order to properly stretch the bolts. I also decided to install a new VANOS high pressure line and engine mounts. Leaking VANOS high pressure lines is another common failure for the S85 cars due to the line not having a proper bend to attach to the VANOS pump. A lot of the folks on M5board suggested swapping this line out with rod bearings while the car is apart so I decided to do the same. The engine mounts I also threw into the job since they would be easily accessible and my current ones already had over 80k miles of use. I basically vouched for a whole refresh of that engine bay area for preventative measures.
Some fellow M5 owners question me as to why I would change out my bearings when my Blackstone reports looked great. Three words: Peace Of Mind. Every few weeks I see a new thread appear on M5board regarding a rod bearing failure. Peace of mind trumps all in my book and the cost of a rod bearing job is much cheaper than having to buy a new engine God forbid the worst happens. It's important to me to do whatever I can to keep my engine running strong and healthy and preventative maintenance is the path I use for accomplishing that.