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Originally Posted by sunsweet
I did not realize a rod bearing is so cheap (machining the crankshaft isn't).
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That's $4 for WPC treatment on each bearing. You still have to buy the bearings themselves. But yes, $400 is cheaper than machining the crank.
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The technical probing and volunteering of information and insights given by forum members deserve praise, but I do not see clear evidences that a significant number of stock engines have failed in so many years. Is it 1 in a thousand ? If the problem had started to be known publicly in 2011, then bmw who has the full database of failed engines was certainly on it too and would have made changes to new cars for 2012 and 2013 model years. Especially if any significant numbers of stock engines under warranty had failed in numbers but I see the large majority of these examples are SC. How many known stock engines failures are we talking about grand total ? 3, 5 ?
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If only supercharged motors were experiencing rod bearing failure, then nobody would be investigating -- I know I wouldn't. The fact that so many NA engines are having rod bearing failure was my motivation for trying to figure out why it's happening. Since it was my engine builder who made the discovery and alerted me to the problem, I wanted to know how much evidence I could find. I also wanted to verify his measurements with those of my own.
As of now, there are many orders of magnitudes of NA motors failing than supercharged motors. As I mentioned in the top articles, if you made it past 25000 miles, then you would likely make it past your entire warranty period. All along, I have been speaking of NA motors, not supercharged motors, though I will include photos of supercharged bearing failures as well in the photo database.
Over the past five years, I've probably seen 25-30 failed NA engines on this forum, not just 3-5. I think I've already posted pictures of five, and have many more to go. Most M3 owners aren't on the forums, so you don't hear about the problems. Last week alone, our local dealer had three M3's with rod bearing failure. Two months ago, a local guy blew his engine with rod bearing failure and punched a hole in the side of his block. Three days ago, it happened to another local buddy. All of these are NA cars under warranty -- and all just in my own area. None of them are supercharged.
Even if BMW knew there was a problem, I don't see them changing the engine design unless it's financially cheaper than replacing engines under warranty. A recall has all kinds of negative financial consequences, and changing the design without a recall could lead to a class action lawsuit and plumetting sales, etc. So BMW isn't going to change the design without a recall; they'd rather roll the dice and know that 99% of all engines will make it out of warranty even if 1% don't.
This Wiki thread was created to spread information about rod bearing clearance and measurements. The clearance issue was discovered without looking for it. But once it was found, it became a very compelling set of evidence to explain so many NA engine failures. But the story isn't over yet, there's another shoe about to fall. Bearing clearance isn't the only problem we discovered. Hopefully I'll have time to gather the pictures and write that article tomorrow.