BMW (finally) publishes S65 Rod Bearing Clearance Specs

[Green-Eggs]

There's a new and "shocking" development for the people following the BMW S65 rod bearing issue. After 10+ years, BMW has finally published their rod bearing clearance specifications. To put it mildly, the specs are shocking and are worse than we had imagined.

Every time a new TIS is published, Bert checks to see if BMW has finally published the rod bearing clearance specs. Such was the case last week when Bert was researching the rod bearing specs for S63 motor. That's when Bert pulled up the S65 engine specs, and noticed that they finally contain rod bearing clearances. [LINK]

The specs aren't good and confirm a worse-than worst case scenario. When Van Dyne measured the original bearings @ 0.0013 inch, they didn't imagine that was at the top end of the clearance specs. Stewart Van Dyne gave the following comment over the phone: "Well, BMW just confirmed that they're doing what we all know doesn't work."

Minimum clearance: 0.0004 inch
Nominal clearance: 0.0009 inch
Maximum clearance: 0.0013 inch



* Same information is posted in the Bearing Clearance Wiki thread.

[Helmsman]

Thanks Green-Eggs, how interesting! Yeah certainly seems to be on the (extremely) tight side and assumingly a good reason to the wear issues we see. BMW engineering certainly been around so bit of a mystery.

These numbers also make me curious about your own measurement of BMWs shell which comes out with quite a bit more clearance?

Nominal Rod Bearing Clearance 0.0381mm
Bearing Clearance Variance 0.0292 - 0.0508mm

Just trying to understand what we're comparing here.

Thanks

[Siajoon]

So does this mean all of us who paid out of Pocket are going to get reimbursed for our RB job... loll

[slicer]

Link doesn't provide the same info found in body of your post. Is there another location with that info. Thanks for posting this!

[Helmsman]

Originally Posted by slicer

Link doesn't provide the same info found in body of your post. Is there another location with that info. Thanks for posting this!

Believe it does: 10-34um with the 22um half way inbetween.

[derbo]

so now what?

[slicer]

Originally Posted by Helmsman

Believe it does: 10-34um with the 22um half way inbetween.

I believe that "connecting rod play" is side play - not bearing clearance.

[ItsGary]

Originally Posted by Siajoon

So does this mean all of us who paid out of Pocket are going to get reimbursed for our RB job... loll

One could only hope but that won't happen

[Green-Eggs]

Originally Posted by Helmsman

Thanks Green-Eggs, how interesting! Yeah certainly seems to be on the (extremely) tight side and assumingly a good reason to the wear issues we see. BMW engineering certainly been around so bit of a mystery.

These numbers also make me curious about your own measurement of BMWs shell which comes out with quite a bit more clearance?

Nominal Rod Bearing Clearance 0.0381mm
Bearing Clearance Variance 0.0292 - 0.0508mm

Just trying to understand what we're comparing here.

Thanks

This is just the data, no other comparisons are implied. We'll leave that to others to discuss and debate.

One thing about those numbers, you' pulled them from the 702 bearings, not the 088 bearings. Since these specs just appeared 10+ years later, we have no idea whether they are for both bearings or not. My personal opinion is that the specs between 088 and 702 bearings didn't change. I know that goes against the general opinions of others. I think those measurement differences are rather insignificant. 0.5/10000 to 2/10000 of an inch difference between paper specs and measured specs is pretty insignificant IMO.

[Green-Eggs]

Originally Posted by slicer

Link doesn't provide the same info found in body of your post. Is there another location with that info. Thanks for posting this!

Originally Posted by Helmsman

Believe it does: 10-34um with the 22um half way inbetween.

Correct. The numbers are the same.

[Green-Eggs]

Originally Posted by slicer

I believe that "connecting rod play" is side play - not bearing clearance.

Bert looked at this and discounted it for two reasons:
1. Side clearance is typically 10x - 35x larger than these values. If these were side clearance values, the engine wouldn't last.
2. The S63TU engine and other BMW engines also list these specs but add the word "Radial" to them. For S63TU, it's very clearly bearing clearance specs as the wording is consistent across many BMW engines. Here's the link: https://www.newtis.info/tisv2/a/en/f...rings/GIecw87b

Still being concerned with the odd wording, Bert checked with Indy and NASCAR engine builder friends. Both confirmed it meant rod bearing clearance; side clearance was therefore excluded.

[tdott]

Great to finally get confirmation what we pretty much knew all along. Or actually it is slightly worse than we thought, but we knew it was less than industry standards.

Queue those who don't know anything coming in to say...."but BMW must know what they were doing and must have done it for a reason."

[dparm]

Originally Posted by tdott

Great to finally get confirmation what we pretty much knew all along. Or actually it is slightly worse than we thought, but we knew it was less than industry standards.

Queue those who don't know anything coming in to say...."but BMW must know what they were doing and must have done it for a reason."

Well it's not like BMW has never built engines before. A bearing clearance is not something they just arbitrarily pick, this shit goes through a lot of R&D. That being said, we don't have any information about what kind of data led them to that design. It's very possible it was based on bad data.

[SoCalRPM]

Thanks for the info, OP. Similar to what someone asked in the parallel thread on this issue - why did BMW do this?

Perhaps, the tight clearance stems from some kind of performance based standard that originated in F1 or some other racing development? If they carried over specs from race engines that likely see rebuilds long before road-going passenger vehicles ever would, then maybe there wasn't sufficient data on the long-term reliability.

I suppose it's immaterial, the clearance data itself being outside of industry standard should be enough to deter them.

Ultimately, it still comes down to either BMW didn't know, or worse, they didn't care.

[Helmsman]

Originally Posted by Green-Eggs

This is just the data, no other comparisons are implied. We'll leave that to others to discuss and debate.

One thing about those numbers, you' pulled them from the 702 bearings, not the 088 bearings. Since these specs just appeared 10+ years later, we have no idea whether they are for both bearings or not. My personal opinion is that the specs between 088 and 702 bearings didn't change. I know that goes against the general opinions of others. I think those measurement differences are rather insignificant. 0.5/10000 to 2/10000 of an inch difference between paper specs and measured specs is pretty insignificant IMO.

Looking at your (BE's) measure of the 088 shells the number is 0.0152 - 0.0533 also with an assumed average of ~0.04mm clearance, again almost twice the assumed average of BMW. With a difference that big something is in my mind strange.
For what its worth it seems that at least the 702 shell often comes out around 0.04mm using plastigage, which would match your own number pretty well.

[Assimilator1]

Old thread I know, but still relevant.

I've recently been involved in an argument over at m3cutters regarding S65 bearing clearances and rod bearing problems (some there don't believe it's a clearance problem...).

As a side shoot from that discussion Paul Gros of MAR Motorsport, an official seller of Mahle MotorSport bearings etc (& he's apparently formerly from Mahle itself), has dipped his toes into it, and then in a separate thread posted clearance specs for the OEM lead/copper bearings which he states are not made by Clevite, but by Mahle/Glacier Vandervell and that the "mean clearance was 0.046mm and the grading scheme allowed a total range of 0.029/0.062mm"

It would seem the figures from TIS (& AIR) are not the rod bearing clearances....
And it would seem the OEM mean (nominal) figures aren't as tight as we thought, although still less than industry standard and BE bearings and Mahle Motorsports own bearings.
Seems to me the OEM ones are still somewhat on the tight side, especially at the lower end, just a little less tight than we originally thought (in respect to nominal clearances, not measured).

Thoughts?

[charliev68]

Does anyone know of any other engine that runs a similar tight tolerance successfully?

[DrFerry]

Originally Posted by Assimilator1

Old thread I know, but still relevant. I've recently been involved in an argument over at m3cutters regarding S65 bearing clearances and rod bearing problems (some there don't believe it's a clearance problem...).

As a side shoot from that discussion Paul Gros of MAR Motorsport, an official seller of Mahle MotorSport bearings etc (& he's apparently formerly from Mahle itself), has dipped his toes into it, and then in a separate thread posted clearance specs for the OEM lead/copper bearings which he states are not made by Clevite, but by Mahle/Glacier Vandervell and that the "mean clearance was 0.046mm and the grading scheme allowed a total range of 0.029/0.062mm"

It would seem the figures from TIS (& AIR) are not the rod bearing clearances.... And it would seem the OEM mean (nominal) figures aren't as tight as we thought, although still less than industry standard and BE bearings and Mahle Motorsports own bearings. Seems to me the OEM ones are still somewhat on the tight side, especially at the lower end, just a little less tight than we originally thought (in respect to nominal clearances, not measured). Thoughts?

What is the source of information posted by Paul Gros? Sorry for not reading his entire thread. Not that it matters, but over the last 14 years of contributing to this forum I developed quite a negative view of the U.K. based m3cutters forum (and some of its members) especially with regard to the entire S65 rod bearing saga. Paging "Green-Eggs".

[DrFerry]

Originally Posted by charliev68

Does anyone know of any other engine that runs a similar tight tolerance successfully?

The Honda S2000
Honda S2000 (F22C1)
Engine capacity - 2 ltr
Engine power - 237 hp
Hp/ltr - 118.5
Redline - 8000 RPM
Preferred oil spec - 5w30
Rod bearing clearance variance - 0.02-0.06mm
Crankshaft pin/rod journal diameter - 49.988mm
Clearance to Journal Size Ratio - 0.008mm

S65 specs
Engine capacity - 4 lts
Engine power - 414 bhp
Bhp/ltr - 103.5
Redline - 8300 RPM
Spec'd oil - 10w60
Nominal rod bearing clearance - 0.0381mm (0.00150")
Rod bearing clearance variance - 0.0292 - 0.0508 mm (from BE's S65 wiki for the later Alu/tin shells, which apparently have a slightly higher minimum)
Crankshaft pin/rod journal diameter - 51.9786-51.9887 mm (official specs posted in the S65 wiki)
Clearance to Journal Size Ratio - 0.0007mm

Source Assimilator1 's thread:
https://www.m3post.com/forums/showthread.php?t=1827360

[Adam M]

I started the initial discussion thread over on m3cutters and after a private email conversation with paulgros, I found myself hanging on his every word. His engineering and specifically bearing knowledge is almost encyclopedic.

The key point is that the numbers that started this thread are definitely the correct ones for con rod play and con rod play is very much not the same as clearance.

It seems that a lot of people have been taken in by an incorrect assumption.

The oem nominal clearance is certainly bigger than is being touted here. Main reason for UK skepticism is the disproportionate number of failures you have had compared with us. It suggests there’s something else going on, other than just slightly lower than normal rod bearing clearance.

[2226cc]

Originally Posted by DrFerry

The Honda S2000
Honda S2000 (F22C1)
Engine capacity - 2 ltr
Engine power - 237 hp
Hp/ltr - 118.5
Redline - 8000 RPM
Preferred oil spec - 5w30
Rod bearing clearance variance - 0.02-0.06mm
Crankshaft pin/rod journal diameter - 49.988mm
Clearance to Journal Size Ratio - 0.008mm

S65 specs
Engine capacity - 4 lts
Engine power - 414 bhp
Bhp/ltr - 103.5
Redline - 8300 RPM
Spec'd oil - 10w60
Nominal rod bearing clearance - 0.0381mm (0.00150")
Rod bearing clearance variance - 0.0292 - 0.0508 mm (from BE's S65 wiki for the later Alu/tin shells, which apparently have a slightly higher minimum)
Crankshaft pin/rod journal diameter - 51.9786-51.9887 mm (official specs posted in the S65 wiki)
Clearance to Journal Size Ratio - 0.0007mm

Source Assimilator1 's thread:
https://www.m3post.com/forums/showthread.php?t=1827360

Interesting to see the difference in chosen oil thickness, I’m running a high quality 5w40 in my s65 and really curious how the bearing will look, probably doing them next winter

[PaulGros]

Originally Posted by DrFerry

What is the source of information posted by Paul Gros? Sorry for not reading his entire thread. Not that it matters, but over the last 14 years of contributing to this forum I developed quite a negative view of the U.K. based m3cutters forum (and some of its members) especially with regard to the entire S65 rod bearing saga. Paging "Green-Eggs".

The source of the information is the original Glacier Vandervell drawing.