Rod Bearing Break-in (hint: there isn't a need)

[IamFODI]

FWIW, I recently came across a PDF from Glyco (attached) that has this nugget on page 10:

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.

I don't know what "minimal" means in this context, so I can't say how widely applicable this, but... does this count as break-in? Looks like it to me. Maybe it's only for some applications.


Side note: I do know Andre is wrong on ZDDP in engine oils. Many modern oil standards have imposed limits on phosphorus and/or other chemical properties (e.g. ash formation) that force a reduction of ZDDP content, but it hasn't been eliminated entirely from car engine oils. Also, modern forms of ZDDP are more effective and there are other anti-wear chemistries available, so it's not necessarily a given that modern oils have poor anti-wear performance.

[mrgizmo04]

Incorrect on several counts:
-They were never specced too tight-- that was the s65 and s85. S54 bearings follow conventional engine design theory on bearing clearances
-the spec didn't change. The original batch of bearing were manufactured incorrectly. The bearings that replaced them were built to the original spec, just thing time they were made correctly.
-if they had been too tight, going to a thicker oil would have exacerbated the situation
-the engine was originally designed for 10w-60. We had (m3forum) testimony to that effect from the guy that led the oil team. 5-30 was a last minute change by the marketing team to make it seem like they were easy to maintain cars. When bearings were spinning, the engineers got their way finally.

What does "manufactured incorrectly" mean? I guess they could not have been any narrower before (lol), so my guess is that they were too tight. Narrow = width they take up on the crank, not the thickness of the shell that increases/decreases the space between the rod and the crank. When I say tight/loose I am talking about thickness - space it takes up between rod and crank. Were they manufactured too long resulting in ovaling once the rod cap was torqued?

Once they started manufacturing them correctly (looser) it started making sense with the oil.

I'm happy to learn facts, my spiel is based on prior readings and research years ago about what engine builders like Lang and others thought on the subject specific to S54.

[Obioban]

My take on the TSB comments.

Remember this was written during the chaos around 2003-2004 when they had to do a recall on all cars because the original clearances they engineered were too tight, and did not provide enough of an oil lubrication layer so the bearing shell rode on the cranks a lot resulting in friction/heat/etc and caused the problems at the oil pressure the system could produce and maintain. The bandaid solution that they came up with so they would not lose much $ on at the time, was to increase oil viscosity (I believe they started on these engines at 5-30 and because of this they switched to 10-60), along with making the bearing clearances a bit larger. I think someone in corporate and legal said - better safe than sorry, we know these guys like to go 8k all day, we can't keep replacing these things indefinitely, so let's get them out of our hair for at least 1.2k miles, tell them to use half the rpm range and see if it works. It kinda did. Proper way to do it would be to redesign the crank/bearing/rod width and make the system into a dry sump with higher pressure, but that would be catastrophic in terms of time and cost and then rebuilding every engine.

Incorrect on several counts:
-They were never specced too tight-- that was the s65 and s85. S54 bearings follow conventional engine design theory on bearing clearances
-the spec didn't change. The original batch of bearing were manufactured incorrectly. The bearings that replaced them were built to the original spec, just the this time they were made correctly.
-if they had been too tight, going to a thicker oil would have exacerbated the situation
-the engine was originally designed for 10w-60. We had (m3forum) testimony to that effect from the guy that led the oil team. 5-30 was a last minute change by the marketing team to make it seem like they were easy to maintain cars. When bearings were spinning, the engineers got their way finally.

[mrgizmo04]

My take on the TSB comments.

Remember this was written during the chaos around 2003-2004 when they had to do a recall on all cars because the original clearances they engineered were too tight, and did not provide enough of an oil lubrication layer so the bearing shell rode on the cranks a lot resulting in friction/heat/etc and caused the problems at the oil pressure the system could produce and maintain. The bandaid solution that they came up with so they would not lose much $ on at the time, was to increase oil viscosity (I believe they started on these engines at 5-30 and because of this they switched to 10-60), along with making the bearing clearances a bit larger. I think someone in corporate and legal said - better safe than sorry, we know these guys like to go 8k all day, we can't keep replacing these things indefinitely, so let's get them out of our hair for at least 1.2k miles, tell them to use half the rpm range and see if it works. It kinda did. Proper way to do it would be to redesign the crank/bearing/rod width and make the system into a dry sump with higher pressure, but that would be catastrophic in terms of time and cost and then rebuilding every engine.

The 10-60 oil is a bit of a catch 22. It is super thick when the car is cold (think of honey or molasses trying cover and roll on the spoon, basically exact analogy) and that increases resistance to being pumped everywhere it needs to go and that decreases the pressure. However the oil needs to be this thick in order to keep up (best it can) with proper lubrication at high rpm at the pressure the pump is able to generate and maintain when the car is being beat on and the temps climb.

The summary is - I'm not sure how much I trust engineers or corporate or lawyers who originally designed something incorrectly and put a band aid fix on it (and all the other fun areas on this car like vanos and subframes and diff clutch - they just can't seem to get clearances and tolerances right 😁 including the subframe body cavity). Take it easy on the car when it is cold and start opening it up only when the OIL temp gets up to operating, NOT the coolant (which I think most folks use as the indicator for when to start sending it). If you do send it a lot once it is up to temp, just reduce your oci and give it fresh oil more frequently. Also keep an eye on oil levels - higher mileage cars that might burn some or leak. Treat the bearings as a maintenance item every ~75k miles. I will not get into Blackstone tests in this thread .

[oceansize]

Just what I wanted to see before I do mine. Gulp....

[mrgizmo04]

One of the local M3 owners posted this the other day. He had just bought the car and it was making a ticking sound but he thought it just needed a valve adjustment. Now the block is well ventilated with a total of 5 windows. It looks like someone messed up the rod bearing replacement.

That sucks. Did he post on facebook that he had a ticking noise, got responses that "it's normal", to which he said, "thanks, sending it"...?

[Mspir3d]

What's more important than break-in is proper install. Which is what I think individuals nerf when they have rod bearing failure after a replacement.

One of the local M3 owners posted this the other day. He had just bought the car and it was making a ticking sound but he thought it just needed a valve adjustment. Now the block is well ventilated with a total of 5 windows. It looks like someone messed up the rod bearing replacement.

[mrgizmo04]

☝️full send 👍

[liam821]

When I'm breaking in the engine in my race car it's start the car on crappy oil, idle until operating temperature checking for leaks etc, change the oil to your oil of preference, strap it to a dyno and let it eat.

[terra]

Where is the max RPM logged on the DME? The service bulletin states, "reprogram DME control module" after rod bearing service is performed. There is also something about the SMG control module - http://www.siwilson.com/BMW/Service_...20Bulletin.pdf

It’s not stored with the program/tune. Newer software may have had more aggressive knock control or something as a last ditch effort to protect the bearings.

[Slideways]

Yeah, but I doubt anyone who got it done back then is still working on reaching the break-in period.

In any case, the dealer actually wouldn't be able to tell by the DME since it only records the max RPM *ever* reached. It doesn't keep a continuous log or last X number of drives or anything like that. Very likely the car would have been red lined at least once before being brought in for a bearing changed.

Where is the max RPM logged on the DME? The service bulletin states, "reprogram DME control module" after rod bearing service is performed. There is also something about the SMG control module - http://www.siwilson.com/BMW/Service_...20Bulletin.pdf

[terra]

Well, it wasn't a 20 year old car 20 years ago when I had the bearings done.

Yeah, but I doubt anyone who got it done back then is still working on reaching the break-in period.

In any case, the dealer actually wouldn't be able to tell by the DME since it only records the max RPM *ever* reached. It doesn't keep a continuous log or last X number of drives or anything like that. Very likely the car would have been red lined at least once before being brought in for a bearing changed.

[mrgizmo04]

In the stack of crank->layer of oil->bearing shell->rod/cap there are 2 variables that can change thickness and distance between the crank and the rod/cap. Original tolerances in the engine were built to have fresh bearing shells. Oil layer changes based on temp and oil pressure and acts somewhat like a dampening spring, as does the softer layer of the bearing shell (lead, followed by a harder layer - copper). It's not always just rotational friction, but there is also impact of the bearing shell onto the crank (from bigger boom in the combustion chamber that sends the piston flying a tad bit faster than the crank is spinning away from it, generating contact and hot spots that wear the much weaker bearing shell material instead of the crank when you ask for higher load from the engine). As the bearing wears some of that space is then taken up by more of the oil, but there is also more (tiny talking microns) distance created between the crank and the bearing shell, producing a tiny drop in pressure. Oil viscosity drops with temperature as the engine warms up and you start wringing it out, and thus pressure drops too. You can also get contact/friction/heat/wear between the crank and the bearing shell by running low on oil (burning it, leaking it, etc) dropping the pressure. Once a new bearing shell is replaced, the thickness of the shell goes back to spec what it was designed to be vs the crank via plastigauge, there are no surfaces that need to wear in together (unlike flywheel/clutch disk/pressure plate, or brake disc/pad where they are hard surfaces meeting each other), you get a slight bump up in pressure from a fresh layer of lead (assuming it were off on the old bearing), you have a film of oil coating it and things are back to hunky dory. The "boom" impact (per above description) is lessened (think of dropping a hammer on a nail head from 3 feet high vs now only from few inches high). If you had to wear them in, how far would you need to do it? What is the new equilibrium? Maybe you should just put the old "worn in" bearings back in?

[Jimbo's M]

Well, it wasn't a 20 year old car 20 years ago when I had the bearings done.

[terra]

I had to do it three times, but as I stated on the old forum, whether I thought it was needed or not is irrelevant. If you don't follow their guidelines, blow your motor and they pull the DME (which is guaranteed), guess who's footing the bill?

On a 20 year old car you’re paying regardless. But yeah, I think it’s reasonable to just follow the break in procedure. Not like any harm results from doing so.