Two of these are not like the others - #5 Rod Bearings Spun

[bigjae46]

I'd be more concerned about the rod. If you heard a knocking noise then the rod is being hammered against the crank. The crank may be ok but the rod end is likely ovaled. Now...will it make a difference street driving? Hard to say, apparently not so far. I'm not sure I could rev the motor to redline with any confidence which is kind of the point of driving an M3.

But weird things happen. Maybe the motor will survive indefinitely but I wouldn't bet on it.

[Ramage]

I'd be more concerned about the rod. If you heard a knocking noise then the rod is being hammered against the crank. The crank may be ok but the rod end is likely ovaled. Now...will it make a difference street driving? Hard to say, apparently not so far. I'm not sure I could rev the motor to redline with any confidence which is kind of the point of driving an M3.

But weird things happen. Maybe the motor will survive indefinitely but I wouldn't bet on it.

Too be clear I am not advocating my current approach, I am simply adding another data point to the rod bearing saga. Anyone reading this now or in the future should be sure to fully inspect the condition of the bearings and crank before proceeding to button it back up. The fact that I missed the condition of the backside of the bearings on cylinder 5 is amateur hour and took a job that is designed to restore confidence in my motor to creating more of an emotional rollercoaster ride than prior to doing the bearings.

In other words if you are NOT 100% sure you are simply replacing worn bearings in known good rods attached to a known good crank than you likely created more anxiety for yourself than you solved, like I did.

What MIGHT have saved this thing so far:

• For the first 1000 miles after changing the bearings I did not go over 5k RPM even though I have always found it odd that we need to "Break-in" hydrodynamic lubricated bearings in an already operating engine... I did it anyway. It was only after those first 1000 miles and sending in my first post bearing swap oil for analysis did I catch the backside of the bearings.
• I caught the knock (not the cold start for 2 - 3 seconds that I heard for a while) on a Thursday and parked it and replaced the bearings on Saturday so it did not knock for long or at anything higher than 4k RPM.
• The journal appeared to be fine - No marks that I could catch a finger nail on.
• My plasti-gage results were consistent and within spec.

I would not bet on it lasting either, and if the cars operation was critical for work or transportation I would have found a way (cannot wait to finish building our house and shop) to get back in there already. For now I am still making the occasional trip to 8200K (no more of less than before) and if it lets go I am prepared to rebuild it.

[Slideways]

If it lasted 1000km, I would not sweat it. Would probably go for a lottery ticket over the oil analysis lol. If it makes you feel any better, Redish MS have a few videos of bearings looking as bad if not worse -

https://youtube.com/shorts/clIzA4tws1Y?si=-TaFTgahQVQ894Bv

On your bearings, you can still see the locating tangs, so the rod should be fine. It is a forged connecting rod and can take some abuse. Fully spinning a bearing and generating a ton friction and heat, now that is a different story.