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      02-17-2019, 10:56 PM   #419
InnerBlueSkies
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Quote:
Originally Posted by Eau Rouge View Post
I have been around these forums a very long time. I can assure you that not everybody that says that they did it by the book actually did it by the book. I am referring to engine break in and allowing the oil temperature to attain the optimal range before going WOT + redline.

Having said that, I do think parts such as rod bearings can fail. I think they will fail more often when the driver / owner disregard recommended best practices by the manufacturer.

We will never know how many rod bearings' failure were due to flawed parts nor how many failures were the result of driver decisions.

Mine has 61k on the odometer and I cannot remember ever having wondered whether bearings would fail on my next road trip.

The whole RB thing, to me, is pointless. If one has a rod bearings concern, drive something else. If it isn't a concern enjoy the BMW model that has the ultimate naturally aspirated engine.

Cheers
I second that motion
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      02-18-2019, 01:20 AM   #420
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If only I knew the engine warm up and driving habits of the previous owner of my M3.

If I purchased my M3 new I probably wouldn't deal with replacement RBs.
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      02-18-2019, 01:30 AM   #421
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Quote:
Originally Posted by Timujin View Post
If only I knew the engine warm up and driving habits of the previous owner of my M3.

If I purchased my M3 new I probably wouldn't deal with replacement RBs.
You probably still would have to deal with it, the bearing shells see wear everytime you start the motor and oil has to flow into the bearings.
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      02-18-2019, 12:51 PM   #422
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Originally Posted by amrazM View Post
You probably still would have to deal with it, the bearing shells see wear everytime you start the motor and oil has to flow into the bearings.
Not really - oil film is still there and when your car starts, it does so under no load conditions and at low RPM. Relative to the forces seen at 8400RPM, startup is not even worth talking about. EDIT: See below for further discussion on startup wear. The intent was not to mislead. Yes, "wear" does happen during startup...

Regardless of warmup etc., if your bearings are too tight, then you will need to replace them or risk spinning one of them.

Cheers,
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Last edited by Scharbag; 02-18-2019 at 02:32 PM.
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      02-18-2019, 01:32 PM   #423
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Quote:
Originally Posted by Scharbag View Post
Not really - oil film is still there and when your car starts, it does so under no load conditions and at low RPM. Relative to the forces seen at 8400RPM, startup is not even worth talking about.

Regardless of warmup etc., if your bearings are too tight, then you will need to replace them or risk spinning one of them.

Cheers,
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      02-18-2019, 01:41 PM   #424
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Quote:
Originally Posted by Timujin View Post
If only I knew the engine warm up and driving habits of the previous owner of my M3.

If I purchased my M3 new I probably wouldn't deal with replacement RBs.
My previous owner had zero modifications and a bicycle rack installed on the roof. Less than 6000 miles a year. Could be a good or bad thing
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      02-18-2019, 01:43 PM   #425
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Quote:
Originally Posted by Scharbag View Post
Not really - oil film is still there and when your car starts, it does so under no load conditions and at low RPM. Relative to the forces seen at 8400RPM, startup is not even worth talking about.

Regardless of warmup etc., if your bearings are too tight, then you will need to replace them or risk spinning one of them.
No, it is a fact that in normally operating engines the most bearing wear occurs at startup. Wear is occurring to the bearings until oil pressure builds which produces the hydrodynamic bearing that the crankshaft rides on during operation. Under oil pressure this fluid bearing prevents the physical contact between bearings and journals.

In addition to every startup, engines with unfavorable tolerance stacking from the factory are hit with the double whammy. Its why we see "babied" engines fail just like those that are tracked. How the engine is treated only speaks to a portion of how the bearings will wear.

You can read about how engine bearings work here:
http://kingbearings.com/files/Engine..._They_Work.pdf
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      02-18-2019, 02:06 PM   #426
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Quote:
Originally Posted by deansbimmer View Post
No, it is a fact that in normally operating engines the most bearing wear occurs at startup. Wear is occurring to the bearings until oil pressure builds which produces the hydrodynamic bearing that the crankshaft rides on during operation. Under oil pressure this fluid bearing prevents the physical contact between bearings and journals.

In addition to every startup, engines with unfavorable tolerance stacking from the factory are hit with the double whammy. Its why we see "babied" engines fail just like those that are tracked. How the engine is treated only speaks to a portion of how the bearings will wear.

You can read about how engine bearings work here:
http://kingbearings.com/files/Engine..._They_Work.pdf
For sure, hence the "not really" comment.

Yes, the majority of "wear" occurs at startup, because the hydrodynamic bearings are not yet operating under pressure. BUT, on a properly designed engine, that wear is soooooo minuscule that we might as well ignore it. If that were not the case, then my buddies 32 year old E30 city commuter would be a paperweight cause he starts that damn thing at least 10 times every day!!

Now, if you drive a cold engine hard right after startup, then that is a recipe for additional wear, and a good hard slap.

By no means am I disagreeing with you sir. You know far more about engines than I do. I do think it is important to clarify that the normal startup "wear" would never cause a rod bearing to look like some that have been pulled from S65 engines. The issue with the S65 is that under load, and at higher RPM, the rod bearings are NOT operating as a proper hydrodynamic bearings.

Cheers,
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Last edited by Scharbag; 02-18-2019 at 02:33 PM.
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      02-18-2019, 02:28 PM   #427
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Quote:
Originally Posted by Scharbag View Post
I do think it is important to clarify that the normal startup "wear" would never cause a rod bearing to look like some that have been pulled from S65 engines. The issue with the S65 is that under load, and at higher RPM, the rod bearings are NOT operating as a proper hydrodynamic bearings.
This is key and why I felt your last post could have been misleading to some readers. If you're considering that startup accounts for some .00001% of an engine's run time then it could be said that it is not worth considering.

The fluid bearing in stock S65's is inadequate indeed compared to an M20, but factually the most wear per revolution does still occur during startup. Carry on.
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      02-18-2019, 08:22 PM   #428
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Quote:
Originally Posted by deansbimmer View Post
This is key and why I felt your last post could have been misleading to some readers. If you're considering that startup accounts for some .00001% of an engine's run time then it could be said that it is not worth considering.

The fluid bearing in stock S65's is inadequate indeed compared to an M20, but factually the most wear per revolution does still occur during startup. Carry on.
I have an 08 with 64000 miles and will likely get the bearings done around 75-100k, most likely at your shop. Im the farthest thing from a mechanic but a lot of times I see reference to start/stop cycles when talking about bearing wear which is consistent with your statement. That said, do the OEM bearings remain inferior once the car is at operating temperature? A lot of us are red light Mario Andrettis, I can't imagine that type of driving and associated loads can be good for any rod bearing...am I correct?
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      02-18-2019, 09:16 PM   #429
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Quote:
Originally Posted by InnerBlueSkies View Post
That said, do the OEM bearings remain inferior once the car is at operating temperature?
Yes. Inadequate OEM clearances remain inadequate regardless of engine temperature. Extra clearance bearings like BE bring the dimensions back to the industry suggested .001" per journal inch.
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