Break-in Procedure

[Obioban]

If you are in the BMW says so therefore i will follow camp fair enough cant expect the average/lay person with zero technical understanding (and not interested in improving) to think much about this stuff but if you're an enthusiast don't pretend there's a technical reason for it just because BMW says to do it. The OP knows BMW says so.

It's better to understand (or try to) whats going on otherwise what will you do in life when there is no procedure. This is an enthusiast forum if you cant handle discussions and differing (informed) opinion then why are you posting in this thread? i'm all for people with alternate opinions but if you aren't prepared to be called out on them if they are flawed then..........BMW says so is not a valid opinion that adds anything useful to the discussion.

I'd give up on the bad analogies (should have used cartilage), the rod bearings will always wear out eventually if you use the engine as intended, even if you had a 6k redline they still wear out on automotive applications they are sacrificial parts. on other equipment they can outlast the equipment life when done properly

Here is a quote from the company that makes BMW's revised s65/s85 bearings (Glyco):

If the clearance is minimal there is good conformability between the bearing and crankshaft journal. This conformability is a result of material that is worn in some parts of the bearing in the order of magnitude of μms. This process leads to less local stress on the sliding layer, a better absorption of shock loads and less wear.

So there's your rod bearing break in benefit/what's going on.

[digger]

Can you provide the link ? it may be in the context of a "sacrificial" coating that some use e.g. clevite tri armour. Otherwise why is there minmal clearance

[R60BBA]

Rod bearings (or head gaskets for that matter) do not require breaking in.

They are not pistons.

However, for peace of mind it may be worth breaking the engine in after a rod bearings service and dropping the oil after 1,200 miles.

[Obioban]

Can you provide the link ? it may be in the context of a "sacrificial" coating that some use e.g. clevite tri armour. Otherwise why is there minmal clearance

https://nam3forum.com/forums/filedata/fetch?id=42909

[digger]

https://nam3forum.com/forums/filedata/fetch?id=42909

the context was in the amount of clearance used, its fairly straight forward that with larger clearances under during shock loads the supported area is less leading to higher contact stress and vice versa with minimal clearance.

It says nothing about break in creating a magically better finish like with rings which is visible with a profilometer as far as peaks, valleys and plateau.

think about it if you baby the engine the crank wont touch the bearing so how is it even going to break in? if you are trying to break in something the surfaces need to touch .

We wouldn't be having this discussion if the bearing manufacturers specified break in / running in / bedding in as part their procedures and installation guidelines as it would be black or white. yet if you want to find about ring break-in or cam breaking then you don't need to look too hard.

i'm still waiting for where it says you cant go WOT as part of the BMW rod bearing break-in . i expect them to say as as part of full engine break-in.

[Jimbo's M]

For those that go back long enough back to remember this site...

http://www.madrussian.net/m3/faq.shtml#28

Did BMW recall E46 M3's for engine failure related issues?

Technically no: BMW issues a "service action." To quote BMWNA, "The problem has been identified as contamination of the engine lubricating system during assembly in combination with unfavorable tolerances in the engine oil pump for the M3 coupe/convertible produced from October 2001 through February 2002. These cars require replacement of the engine oil pump and as a precautionary measure, replacement of the connecting rod bearings. In addition, the engine control module will be programmed with the latest software, which includes improved cold start characteristics. We ask that you contact your authorized BMW center to arrange a service appointment to have this service action carried out. Your vehicle can still be driven with no immediate need to have the repairs carried out. The service action will take approximately one days work, however, the actual time will vary with center scheduling. BMW of North America, LLC, will cover all necessary repair costs related to this action as well as providing you with alternate transportation if necessary. After the service action is performed on your M car, a 1,200 mile break-in period must be observed. Do not exceed 5,500 engine rpm or 105 mph road speed during this period. Please observe your local & state maximum speed limits. " - This "service action" is being done by VIN number and generally effects 2002 M3's manufactured between October of 2001 and February 2002.

As all can see, no mention of WOT. That said, I know for a fact that I received explicit instructions to avoid full throttle. I had to do this procedure three times, whether WOT was deemed unnecessary for the last two, I honestly am not sure (17-18 years ago) but am willing to bet it was. I am NOT arguing the validity, merely the messenger.