Bmw cylinder wall assessment

Hello everyone,

I recently bought an 09 BMW 750i with the infamous N63 engine. I endoscoped all cylinders, cyl 8 has some markings on it that I have no clue what they are and how much concerned I should be. Would appreciate some expert review. [url=https://www.youtube.com/watch?v=0pyPGadEHBA]https://www.youtube.com/watch?v=0pyPGadEHBA

Thanks!

Not an engine I'm familiar with, but it appears BMW used a Alisil bore finish for it, and if so, those black spots may indicate an area where the alloy wasn't quite as well 'mixed' as expected, and it's breaking down unevenly in thar spot.

https://drjlt.com/article/tech/389/nikasil-alusil-lokasil-silitec

Have you noticed any other issues with that cylinder, more specifically plug fouling or differences from the other cylinders? My personal thoughts are if I liked the car to just keep using it until there is an actual problem with the cylinder, or engine, or even the rest of the car. If I didn't care either way, I'd sell it while it's working fine, which would remove any worries. Either way, you may lose money (like with ANY car), but it's your choice which way that goes.

If you go for the first, and especially if you're thinking of making significant power increases, you can keep using it while you get the money for sleeves, etc.

Thanks for your reply. Correct this is an alusil engine. These engines suffer from valve guide seal issues and they start buring oil. The plug on that cylinder was more fouled than other ones and it was misfiring every once in a while. I switched plugs and it only misfired on the other cyl only. I was planning on replacing the valve seals but not sure if it's worth doing if that cyl is on its way out. I also noticed some scoring, seems minor but not sure also.

Ah, rather than swap plug's around, I'd pick up a box of them and just replace the fouling one when the mis-fire starts.

It's actually bad to run a modern engine with a misfire, as that will show up as excess oxygen at the lambda, and the ECU may try to enrichen the mixture to compensate - the additional fuel used may be expected to be a lot more than the cost of the new spark plugs, and the rich mixture, if it is occuring, will 100% compromise the ring and bore wear by diluting the oil on the cylinder walls, which is the opposite of what you want.