Quote:
Originally Posted by rusnak
Why would a bottom end bearing fail, and not something in the top end? It's as if it's a parts failure or something related to the engine manufacture process.
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That's a very severe lubrication regime upon start-up. That main bearing most likely has the most stress upon it. Not sure about the BMW but until the bearing has established what is called hydrodynamic film formation its at the mercy of boundary film and that is where the most wear occurs during start-up. If you have a tendency to rev you engine at start up your not giving the oil a chance to separate the babbit surface. The more revs with out mixed film or hydrodynamic film and the more times the semi-lubricated surface is presented...more wear sooner.
Its a good reason to not rev the engine at start-up.