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

[Tbonem3]

The BMW break in procedure is about rpms for a particular period (miles), not oil.

[Chanman1029]

Standard M spec 10w60 oil. Let's not have an oil discussion thread here.

Some people also just use oil to lubricate every surface prior to bearing assembly and some use an engine assembly lube. From what I've read, both methods work fine.

its break in oil, in a break in thread, seems pretty relevant to me….

[eljay]

So which oil?

Standard M spec 10w60 oil. Let's not have an oil discussion thread here.

Some people also just use oil to lubricate every surface prior to bearing assembly and some use an engine assembly lube. From what I've read, both methods work fine.

[jet_dogg]

So which oil?

[Tbonem3]

Using a less viscous (when cold) oil doesn't make sense. Just use your regular oil IMO. If in a cold climate, if you're worried, run some euro formula 0-40 or usual bmw spec 5w30.

It's not about possibly making contact or not, it's about seating - making contact on purpose.

Piston rings must take a set in a freshly diamond honed cylinder for maximum compression. The rings scrape the "peaks" created by the honing, to make a flat surface.

You're not preparing the crank to mate with new bearings such that a break in would create a new relationship between the two surfaces. You're not modifying the surface of the crank such that the new bearings will "seat" against it like a cylinder wall.

[Chanman1029]

What sort of break in oil do you recommend? I just did a full rebuild, and was recommended to use 15w-50 break in oil by driven, does that sound right?

[lemoose]

It shouldnt need it- but people in this thread are basing that off the fact that they are supposed to be a contactless surface which is comical because we all know empirically hasnt been the case for this motor- hence why were all here discussing bearing jobs.

unless youre taking the rods out and checking clearances and round with a micrometer- truth is you really dont know if there will be contact. Im willing to bet that 90% of s54 rod bearing jobs dont go to such length. Best case scenario they probably plastigauge it and call it a day. So at least for these jobs, A “break-in” procedure could save you from one of the more catastrophic failure modes for bearing contact.

in any case I dont believe a break in is necessary but thats just because i think the s54 bearing issue stems from a combination of 3 things:
- tight tolerances that made proper oil temp imparative
- accessible price point which led to many novice owners who didnt appreciate the above
- large production numbers for such a high strung motor which amplifies the perceived failure rate

[Syfon]

Rod bearings don't require break-in.

If you're motor is brand new or freshly built, different story altogether.

If you've just replaced rod-bearings as a course of routine maintenance, breaking them in is a waste of time. Always wait for oil to reach temp, then send it. Per usual.

[jbfrancis3]

Maybe I should've broken in my new tube of toothpaste

[tnord]

maybe not valve adjustments, but we should break in water pumps and alternators, they have bearings too you know!

[Tbonem3]

Poor logic.

If it doesn't need it, it doesn't need it.

Should we do a break in after valve adjustments too???

[Tjkenny15]

Seems silly not to break in rod bearings, for any car, even if it isn't 100% necessary. You just spent a lot of time and money to get your s54 healthy again, seems foolish not to.

I break in literally everything, electronics, rotors, pads, my car battery, shoes... its peace of mind at the end of the day.

[tnord]

In an ideal world bearings don't touch the crank. In the same ideal same world, S54 bearings wouldn't have a wear issue to begin with.

this ideal world is where every other mfg lives.

[lemoose]

In an ideal world bearings don't touch the crank. In the same ideal same world, S54 bearings wouldn't have a wear issue to begin with.

[tnord]

Just throwing this out as a "yeah but" as I have little idea...but, does Mazda have a motor with piston speeds that the S54 has which upon debut was just shy of the BWM F1 V10 of the day? Maybe that matters a little..

I don't think that really matters. Mazda's warranty exceeds BMW and they would be more interested in longevity. I'd be surprised if Mazda's PPI procedure was unique also. Specialist cars like Singer, run their engines on an engine dyno prior to installation. Do you think they limit that to 5500 rpm?

What I can't wrap my head around is why they had that procedure to start with. Did they know they f'd up before production and put that procedure in there to try and avoid catastrophic failure?

That said, in the case of rod bearing replacement, I agree that you've got nothing to lose (other than having the patience to drive that way for 1k miles) by following the procedure. I actually just got my car back from rod bearing replacement a couple days ago, and I'll sort-of be following it. The shop drove it around a bit keeping it under 4500 to make sure all was good, I've probably driven it another 20miles not exceeding 6k rpm, but I've probably hit full throttle a few times. I have a 400mile road trip coming up where it won't be difficult to baby it, so I'll probably do that then call it good.