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Discussion Starter · #1 · (Edited)
I've spent several hours the past few days reading the rod bearing threads and find them very interesting, and I'm even more impressed now by the knowlege on this board. You can get quickly up to speed on the issues after 4 or 5 twenty page threads and their sublinks.

What bothers me is the inability to determine that there is a problem brewing before a catastrophic failure; hence the preventative maintenance strategy of replacing them. I'm not one to argue against replacing known weak links before they make their presence known but on the other hand, I don't want to open up my car's chest cavity just to confirm it's heart is still in good condition. Anytime we open an engine, there's the risk of knock-on effects (dust on bearings, incorrect torque settings when reassembled, etc.) Also, we operate under the assumption that the repair will be done correctly, but we know this is not always the case. That's why we don't just let anyone work on an M5 engine; especially if it's to save a couple hundred dollars.

But here's what I'm thinking and hope some of you can tell me why this will/won't work. The failures occur following wear on the bearings. The wear means metal is being removed. Although the bearings can't be seen until they're removed, I would think the metal would end up in the oil.
Blackstone oil analysis measures metal content in oil and compares it against an expected norm. Could an oil analysis, or series of analyses, especially after track days detect the metal?

Which brings up my related questions; What metal is the actual bearing made of? I assume it's a base metal with a specific second layer as a coating. Anyone know what that top coating is made of? If the particular metal is used in multiple internal parts, using it's presence in oil as a potential indicator of rod bearing issues is difficult; however if the particular metal is only used in rod bearings, it would be more useful information.

Also, do any of you that have had rod bearings replaced, and saw damage to them, still have the oil drained prior to the replacement? If so, it might be interesting to mix it up and send in a sample. I know I sometimes keep oil in my garage until I have an opportunity to take it to a recovery center so I thought it would be worth asking.
 

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Hmmm... far too much logic being presented here :D

I'm a big believer in used oil analysis and use it as another tool in the caring and feeding of the S62 (or any specialty engine). The key is to get multiple tests done over a period of time so that a trend can be recognized. Blackstone themselves will tell you that a single test can be inconclusive, but multiple tests can give you a very clear picture of how your engine is wearing. In addition you'll get average results of all of the S62s that they've tested so you can see how your values stack up in comparison.

Copper and lead are typically going to be the trace metals that will show accelerated bearing wear.
 
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But there is only one way to be really sure...pull them!
Exactly. A high trace metal reading will show that some bearing is wearing, but it could be top or bottom end. High readings give justification for further investigation and based on the history of the S62 the bottom end bearings are the place to start.

Most of the posts here that have shown worn bearings have shown severely worn bearings. This should produce a fairly large spike in trace metal readings. In the absence of a high trace metal reading from a UOA I would be hesitant to open up the bottom end due to potential risks.

The UOA on the S54 in my E46 shows a slightly higher than average reading for copper and lead, but this was on BMW's change interval of 15,000 miles (I just got the car with 56K on it). Both Blackstone and I agree that these values on their own don't warrant tearing into the engine. If they are still higher than normal at the next test (about 5000 miles) then I'll begin looking for a culprit.
 

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Discussion Starter · #5 ·
Amp, I probably do analyze too much. It's a defect associated with being an engineer.:D

From your and VantaaM5's feedback, it appears copper and lead may be the trace elements that would show up. I agree you can't tell from what source the material is coming without going in. I also agree that a series of tests over a longer period would be best. However, determining the source of the material by means of an oil test is secondary to me; determining that excessive bearing wear is occurring within the engine is of primary interest. Because of this, I will send in a sample in a few weeks just to see where the levels are currently in my car.

I did find a couple of interesting writeups that have metallurgy discussions in them. Ignoring the thin babbitt overlay material, copper values should spike if a bearing is wearing excessively I would think. I still think it would also be a good idea to pull an oil sample after changes to the car described by Lcsman such as the addition of a chip, addition of a SC, or significant track time.

King Engine Bearings

Engine Crankshaft Bearings
 
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