I will definitely share once I get the engine torn down but before then I need to source a replacement.
I went to look at an N62 4.8 yesterday and saw this in cylinder 1. This cylinder also had oil on the plug...
It looks to me like this is the beginning stages of the failure that happened to my engine. This was at a local car breaker, so not really sure the history of this engine either.
I do have a 200,000+ mile N62 that doesn't smoke at all so I don't think it affects all N62's, but I am wondering if it affects more than most people realize.
I found this online when researching the topic (page 6
https://lnengineering.com/files/2019...er-Systems.pdf)
Quote:
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Critically important is the use of barrel-shaped piston ring faces, so as to glide across the surface, as opposed to a scraping action caused by some ring types. Excessive ring tension or incompatible ring types can damage the exposed silicon particles, resulting in a failure of the cylinder sliding surface to support the piston and ring system due to plastic deformation of the aluminum matrix
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The N62 technical manual states the pistons have three rings:
First piston ring groove = square ring
Second piston ring groove = taperface ring
Third piston ring groove = three-part oil control ring
I am wondering if incorrect geometry rings (square vs barrel face) are a contributor to the problem. BMW did use Alusil in other applications prior to the N62 (including the M62 which this issue has not been documented on afaik) - but most the Alusil I6's had iron sleeves...
Still trying to figure out the root cause as best as possible in order to avoid buying a replacement engine with the same problem.