Rod bearing wear, up close and personal.

[deansbimmer]

We do a lot of rod bearing jobs here at Mporium and answer a lot of questions on the subject. I wanted to make an informational post to highlight up close views of what the bearing wear looks like under magnification. With most rod bearings coming out looking "not too bad for an S65", this may help clear up some misconceptions and clarify how bad the visible wear really is. Maybe later I will take measurements of the worn bearings compared to new bearings to see how the oil wedge may be disrupted from the abnormal wear. This post isn't very scientific and is only based on my professional experience and ponderings.


Here are the bearings as removed from a 2011 M3 with 69k miles that I just did yesterday (OEM 702/703). As you can see these are typical of the poorly wearing S65 bearings, but a very poor example of how rod bearings are supposed to lookby industry standards.




We will be looking more closely at this bearing, the #7 upper bearing. It has some interesting debris embedded into the babbit layer.




Here is the embedded debris, and the close up. Due to the discoloration I would speculate that it is some steel flashing left over from assembly. Also of note, this shot helps you visualize the "micro-grooving" of the OEM style babbit which aids in oil retention and to flush out debris. See how it has been worn almost flat, with only the groove valleys still visible.





Here is the parting edge of the matching lower shell. It shows the resulting wear from a slight crush, as well as some delamination of the babbit layer at the corners.



On the back of the bearings we see the cross-hatching which is a physical imprint from the honing process of the rods. This is quite functional in that it is the main mechanical method of securing the bearing shells from rotation (a spun bearing). Contrary to popular belief the shell's locator or 'pin' is not what prevents the shells from rotating in the rod bore. Too much (or too little) honing of the rods (and the resulting bore diameter) will affect crush and final bore size/consistency.




Lastly, and perhaps most alarming, we will look at the most highly worn area of the top shell, where the first layer of the babbit has been completely worn away down to the binding layer. .






Up close, we can see that this layer has become so thin that is has some perforations in it from the layer starting to break down. It will continue to craze and break apart until delaminating altogether which is when your rod will start to knock, or the journal will seize altogether. Since we can't track these bearings for abnormal wear in oil analyses, nobody can know how close their journals are to this state without removal. This is why we replace these as preventative maintenance. Under extreme magnification, we start to see how poor these bearings really look..





To compare wear to an older style lead/copper OEM 088/089 bearing with similar miles (78K), here is an upper shell showing typical S65 wear, that we will get close to in the next photo.. It's easy to see the lead literally flaking from the babbit.






Being a softer metal, its edges do not "feather" as smoothly as the later style bearings of harder composition. These particles that flake off are what we look for in oil analyses. The elevated lead content is what tells owners that there is poor wear. Abnormally high levels are alarming, and when the lead and its binding layer is worn through to the copper underneath, the red flags are raised and alarm sirens should sound. It's time to replace the bearings. This is also why replacement with lead/copper type bearings such as BE is preferable to replacement with new 702/703 OEM or even WPC treated OEM bearings with no uniquely traceable metals.








Lastly, we see what can happen when rod bearings are not replaced preventatively. Total carnage.

[aswy6]

Thank you very much for this post! Gotta do stuff like this more often)

[pbonsalb]

That was very helpful to those of us who are not professional mechanics or engine builders.

[donut_boi]

Thank you for the great in depth explanation as well up close pictures!

[6ixSpd]

Great write up! Good to know what constitutes wear and tear on these bearings.

[SYT_Shadow]

Thank you, great post

[Helmsman]

Thanks Deansbimmer, like always interesting input!

[Redd]

Deansbimmer, what's your view on BE bearings? Are they lifetime parts? If not, what are the recommended change intervals for BE vs OEM bearings?

[Teufel_Hunden]

Great lesson. Thank you!

[admranger]

Originally Posted by Redd

Deansbimmer, what's your view on BE bearings? Are they lifetime parts? If not, what are the recommended change intervals for BE vs OEM bearings?

No bearings are lifetime parts. The replacement interval will be determined as people get more miles on their cars is my guess.

SYT_Shadow goes through withdrawal symptoms if he isn't spinning wrenches so I imagine we'll see him pull his BE bearings at some point in a year or two.

[deansbimmer]

Right. No bearings are technically lifetime parts but bearings in most engines go hundreds of thousands of miles without being replaced. Since BMW decided to employ abnormally close bearing tolerances in many of their ///M engines, especially the S65 (See HERE and HERE) we see accelerated wear to the bearings which is not normal for gasoline engines. The leading solution so far has been to increase the clearance closer to the industry standard with custom bearings (BE Bearings) which should return lifespan of the S65's bearings back to the 100-200k mile lifespan typical of most engine bearings. Since it takes time to rack up that kind of mileage in an M3, it will be a while until we can start stating it as a proven and 'permanent' solution.

[SYT_Shadow]

Originally Posted by admranger

No bearings are lifetime parts. The replacement interval will be determined as people get more miles on their cars is my guess.

SYT_Shadow goes through withdrawal symptoms if he isn't spinning wrenches so I imagine we'll see him pull his BE bearings at some point in a year or two.

I'm not sure about withdrawal syndrome, but I have committed to pull then after 100 track days. At the latest that will be next year

[Scharbag]

That is quite the chunk of swarf that was embedded in the 702/703 bearing. Another reason that lead/copper bearings are nice to have as the babbitt is softer. Was there any crank scoring on that journal? It looks like that chunk got hot by its coloration.

Thanks for the great information.

Cheers,

[Redd]

That's my concern. There is quite a fair bit of data now on how long the OEM bearings last but almost zero on the BE bearings. 100-200k miles is a huge gap. I somehow feel safer with OEM as I know when to preemptively replace them.

[deansbimmer]

Originally Posted by Scharbag

That is quite the chuck of swarf that was embedded in the 702/703 bearing. Another reason that lead/copper bearings are nice to have as the babbitt is softer. Was there any crank scoring on that journal? It looks like that chunk got hot by its coloration.

Thanks for the great information.

Cheers,

Luckily there was no damage to the journal. Yes, aside from being able to track wear via oil analysis, the softer face of the lead/copper bearings also embeds debris better than the harder tin bearings. The engines I've seen fail with the harder bearings have utterly destroyed journals. I've been able to save cranks from failed engines with the 088/089 lead bearings. It's just a couple of the reasons why I can't understand why people would use oem when you could use Pb/Cu bearings.

[deansbimmer]

Originally Posted by Redd

That's my concern. There is quite a fair bit of data now on how long the OEM bearings last but almost zero on the BE bearings. 100-200k miles is a huge gap. I somehow feel safer with OEM as I know when to preemptively replace them.

That may be an understandable viewpoint for a layman. I consider low BE feedback as good, as "no news is good news" here. Hundreds (thousands?) of failed OEM bearings from 13k miles to 1xx,xxx miles and everything in between. There's no comfort in that inconsistency for me. Thousands of BE bearings in engines out there with no bearing failures that I've heard about. That would still make hundreds of thousands of cumulative miles in BE bearing'd engines.

[NeverL8]

Originally Posted by deansbimmer

That may be an understandable viewpoint for a layman. I consider low BE feedback as good, as "no news is good news" here. Hundreds (thousands?) of failed OEM bearings from 13k miles to 1xx,xxx miles and everything in between. There's no comfort in that inconsistency for me. Thousands of BE bearings in engines out there with no bearing failures that I've heard about. That would still make hundreds of thousands of cumulative miles in BE bearing'd engines.

What is your view on VAC? (besides the inventory confusion that happened while back) strictly as a product, not customer service

[deansbimmer]

Originally Posted by TheRussski

What is your view on VAC? (besides the inventory confusion that happened while back) strictly as a product, not customer service

I've installed a lot of VAC bearings which are a fine product but I prefer BE whenever possible. VAC is undeniably better than OEM but still do not provide the .001" clearance per journal inch that the industry suggests (ref HERE) and is typical with other engines. With our journal size and oil spec, .0024 nominal clearance is what we find as an ideal starting point. This is what BE targets with their bearing sets. VAC is closer to .0020 which is only a bit larger than the OEM 702/703 at .0017 nominal (ref HERE). Bottom line IMO is that it's most important to just get new bearings in your engine. With that said, if I'm going to do the job I'm going to choose the aftermarket bearings with the most published engineering background to support the theory of a sizing deficiency, and that remedies it. Also see HERE for more BE support (zero anything from VAC)

[Richbot]

Thanks for getting some good closeups. Can you shoot a few mains too? Would be curious to see wear patterns side by side and most of us don't have access, thankfully, to our main bearings yet.

[G80indy]

Doesn't this reinforce the thinking to change oil at break-in, often, perhaps multiple times....
Perhaps at 200, 500, and 1000 miles...
Especially if the particles are suspected to be in there from engine assembly.

[deansbimmer]

Originally Posted by Richbot

Thanks for getting some good closeups. Can you shoot a few mains too? Would be curious to see wear patterns side by side and most of us don't have access, thankfully, to our main bearings yet.

Here is a set real quick. These failed in a 2010 w/56k. I have other unfailed sets I'll get up too when I get a minute.

[kyrix1st]

Originally Posted by 330indy

Doesn't this reinforce the thinking to change oil at break-in, often, perhaps multiple times....
Perhaps at 200, 500, and 1000 miles...
Especially if the particles are suspected to be in there from engine assembly.

I think I read a paper somewhere that ~50% of particles are from debris past air filter and fuel. low mileage OCI can't hurt.

Also seen a UOA that break-in oil has around 11.0 cSt at 1200 mile service without any moly or boron so it is suspected to be a mineral based 5w-30/0w40, so major wear components should have been flushed if break in procedure was properly followed.

Here's the link: http://www.m3post.com/forums/showthread.php?t=848738