S65 Engine Main Bearing Service, Documented

[Watermelon6161]

Unfortunately, today when I planned to replace my 09 E90M3 with 130,000 kilometers on it, I discovered scratches on one of the crankshafts, clearly caused by metal shavings. What should I do? Do I need to replace the crankshaft? I'm devastated.

[deansbimmer]

Originally Posted by Watermelon6161

Unfortunately, today when I planned to replace my 09 E90M3 with 130,000 kilometers on it, I discovered scratches on one of the crankshafts, clearly caused by metal shavings. What should I do? Do I need to replace the crankshaft? I'm devastated.

That type of damage is problematic, and would certainly necessitate engine removal for replacement of the crankshaft for a correct repair. With that said- that type of damage has resulted from imperfections in the crankshaft and created valleys in the hardened layer of the crankshaft. The damage is not proud of the journal's surface like most type of scoring. The journal *can* still function if needed, and obviously has remained functional since the damage occurred.

The best route is removal and rebuild. However if that is not possible and you feel adventurous or in an experimental mood, I would check the journal carefully and confirm there are no proud gouges, clean it up as best as possible and install new bearings. Reassemble and see how long you can go. You might be surprised how many more miles the engine will go.

[DrFerry]

Originally Posted by Watermelon6161

Unfortunately, today when I planned to replace my 09 E90M3 with 130,000 kilometers on it, I discovered scratches on one of the crankshafts, clearly caused by metal shavings. What should I do? Do I need to replace the crankshaft? I'm devastated.

If you run your finger nail ever so gently over the crank journal markings (shown in the photographs) do you feel the markings are raised or recessed? The reason I ask is I'm wondering "if" what you're seeing is some lead deposition (smearing) transferred from the bearing shell surface onto the crank journal surface? If the marks are just lead deposits from the bearings then I think the journal can be polished and cleaned up. As deansbimmer mentioned "if" the markings are gorges or valleys i.e. not raised the crank could still be cleaned up and returned to service IMO.

[Assimilator1]

As the other guys discussed, if they are grooves (which wouldn't gouge any new bearings) and not raised 'lines' (which would gouge bearings), then I'd be installing new bearings and seeing how it goes.
Unless a rebuild is not a major issue for you.

Can you see what caused those gouges on the old shells?
Have you got full photos of the shells for that journal?

[Watermelon6161]

Originally Posted by deansbimmer

That type of damage is problematic, and would certainly necessitate engine removal for replacement of the crankshaft for a correct repair. With that said- that type of damage has resulted from imperfections in the crankshaft and created valleys in the hardened layer of the crankshaft. The damage is not proud of the journal's surface like most type of scoring. The journal *can* still function if needed, and obviously has remained functional since the damage occurred.

The best route is removal and rebuild. However if that is not possible and you feel adventurous or in an experimental mood, I would check the journal carefully and confirm there are no proud gouges, clean it up as best as possible and install new bearings. Reassemble and see how long you can go. You might be surprised how many more miles the engine will go.

Thank you very much for your input. It was indeed a difficult decision to make. In the end, I have decided to follow your advice and lightly polish the scratches before installing the new BE tile. I will observe it for a while. It has been installed now, and after a brief test drive, I haven't noticed any other issues so far.

[Watermelon6161]

Originally Posted by DrFerry

If you run your finger nail ever so gently over the crank journal markings (shown in the photographs) do you feel the markings are raised or recessed? The reason I ask is I'm wondering "if" what you're seeing is some lead deposition (smearing) transferred from the bearing shell surface onto the crank journal surface? If the marks are just lead deposits from the bearings then I think the journal can be polished and cleaned up. As deansbimmer mentioned "if" the markings are gorges or valleys i.e. not raised the crank could still be cleaned up and returned to service IMO.

After a slight polishing and the installation of new bearings, nothing has happened yet.

[Watermelon6161]

Originally Posted by Assimilator1

As the other guys discussed, if they are grooves (which wouldn't gouge any new bearings) and not raised 'lines' (which would gouge bearings), then I'd be installing new bearings and seeing how it goes.
Unless a rebuild is not a major issue for you.

Can you see what caused those gouges on the old shells?
Have you got full photos of the shells for that journal?

Upon inspection on site, it was observed that there were metal-like substances on the bearings, indicating the presence of foreign objects during the second installation of the bearings.

[Assimilator1]

Got any more photos of that?

Originally Posted by Watermelon6161

After a slight polishing and the installation of new bearings, nothing has happened yet.

I hope it works out well in the long run too (if I had to bet on it, I'd bet it would last a long time).
Keep us posted.

Oh btw, a similar case to yours, although his shells were much worse, the copper had started flaking off! Is discussed in this thread
He did 28k miles on the scored crank! (with new OEM bearings), then sold it.