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I'm definitely enjoying this. I always thought as well that bearings would self level but of course was just a theory of mines. The whole break in period to allow for things to create it's own clearances and continue functioning given the variables (oil squiters, oil thickness, etc) would correct itself.
 

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The researchers drew the following conclusions:
Abrasive Engine wear can be substantially reduced with an increase in single pass efficiency. Compared to a 40-Micron filter, Gasoline Engine wear was reduced by 50 percent with 30-Micron filtration. Likewise, wear was reduced by 70 percent with 15-Micron filtration. Controlling the abrasive contaminants in the range of 2 to 22 Microns in the lube oil is necessary for controlling Engine wear. "
I'm assuming any oil filter with those specifications would have to be a custom job? I'm only aware of the BMW oem and MAHN paper filters, and the K&P life time metal filter but only goes as low as 35 microns as advertised.

And with how sensitive the vanos system is on this car, cutting the oil flow rate with a more fine filter doesn't negatively impact the system at all?
 

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I would NOT recommend running a stainless mesh filter on really anything, particularly on an S85. Mesh filters are not very efficient for debris removal.
 

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"Could you please elaborate more on the cam phaser bit, if possible in a way for a non engineer?"

Basically the cam phasers (i.e. VANOS actuators) need oil flow to function properly. If the tolerances are loose and/or flow passages large the oil flow goes up. The flow through the cam phaser passages can be decreased via thicker oil (like an old Harley oil spec!). The phaser presumably needs the viscosity to function correctly, so not knowing any better I'd be careful going much thinner than say 5w50 (I backed off 0w40 to 5w50 personally). Torsional and/or just running data could alleviate this concern (which I don't have yet).

"-- would it make the motor more reliable? efficient?"

Reliable, probably no difference. Could improve fuel economy or torque though. Basically the exhaust valve closure can be delayed (thus increasing overlap), which causes exhaust to back-flow into the cylinder. This displaces intake charge mass, which lowers combustion pressures/temperatures to decrease NOx emissions. jcolley's suspicions that I've read elsewhere were correct on why the VANOS map looks like it does.

"Is there a point if you've already put in higher clearance bearings?"

Basically these adjust the clearance to come to the oil. Nothing wrong with that. If you've already got the increased clearance I'd stick with thicker oils. IF the phasers would work correctly with thinner oils, the ~25 micron clearance would match up to say a 5w30 or 0w20 to me...(not having run the bearing calculations here).

I presume that the Schrick cams are a different profile and would still have to be timed/mapped.
 

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I'm assuming any oil filter with those specifications would have to be a custom job? I'm only aware of the BMW oem and MAHN paper filters, and the K&P life time metal filter but only goes as low as 35 microns as advertised.

And with how sensitive the vanos system is on this car, cutting the oil flow rate with a more fine filter doesn't negatively impact the system at all?
EXTRA GUARD Cartridge Oil Filter BMW M5 2008 V10 5.0L | FRAM

I will try this filter once i get my oil pressure gauge installed, i will change out filter after first sign of pressure drop
 

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"Could you please elaborate more on the cam phaser bit, if possible in a way for a non engineer?"

Basically the cam phasers (i.e. VANOS actuators) need oil flow to function properly. If the tolerances are loose and/or flow passages large the oil flow goes up. The flow through the cam phaser passages can be decreased via thicker oil (like an old Harley oil spec!). The phaser presumably needs the viscosity to function correctly, so not knowing any better I'd be careful going much thinner than say 5w50 (I backed off 0w40 to 5w50 personally). Torsional and/or just running data could alleviate this concern (which I don't have yet).

Makes sense, but i recall that in a BMW paper that the intent of the separate Vanos pump run at high pressure was to ensure a sufficient speed of response to keep up with an 8200 rpm motor.
Turns out this was overkill hence the s65 vanos system is much lower pressure that does not require the expensive tight tolerance solenoids


"-- would it make the motor more reliable? efficient?"

Reliable, probably no difference. Could improve fuel economy or torque though. Basically the exhaust valve closure can be delayed (thus increasing overlap), which causes exhaust to back-flow into the cylinder. This displaces intake charge mass, which lowers combustion pressures/temperatures to decrease NOx emissions. jcolley's suspicions that I've read elsewhere were correct on why the VANOS map looks like it does.

"Is there a point if you've already put in higher clearance bearings?"

Basically these adjust the clearance to come to the oil. Nothing wrong with that. If you've already got the increased clearance I'd stick with thicker oils. IF the phasers would work correctly with thinner oils, the ~25 micron clearance would match up to say a 5w30 or 0w20 to me...(not having run the bearing calculations here).

I presume that the Schrick cams are a different profile and would still have to be timed/mapped.
+1 on sticking with 10w-60 once bearings worn
 

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Regarding the location of the wear spot, I don't think there is much disagreement in terms of location. Most of the pictures I've seen are all from S85 and S65s. Engines from other OEM's don't really have this problem at such low mileage. The spot is generally in the 1:00 position, 12:00 being the top of the arc, with 9:00 and 3:00 being the sections when it is split. I agree that there is not much variation in location for rod bearing wear in engines where it oil starvation/lack of proper oil film thickness is the culprit for the wear. The spot is largely dictated by where the the crank journal is in relation to TDC of the piston, the rod length relative to the stroke (more specifically rod ratio) dicates the angles. It is simple geometry, but complicated by rod clearance, and inertia from RPM. Given all the same conditions in the same engine the wear pattern would look different if on cold start the engine was idling at 800 RPM vs. idle on cold start at 4000 RPM.

Regarding whether the S85 has high cylinder pressure, I disagree. Certainly boosted engines like a N54 have far higher cylinder pressures, that is not a fair comparison if that is what you mean to draw. I don't have the data from an instrumented engine with a piezoelectric pressure sensor in the cylinder, but that is the way to measure max cylinder pressure. I also can no longer calculate the theoretical pressures either, but few people care about theory here. That said for a naturally aspirated engine the BMEP and specific power output is quite high for the S85 almost on par with the F20C in the Honda S2K. I would not expect the cylinder pressure of an alusil block engine to compare what can be achieved in the N54 which was designed to be stronger due to it being designed for a turbo. The S85 was designed to be lightweight, the N54 was designed for strength. A 12.0:1 CR is very high especially since the S85 is port injected vs. direct injected. This high CR is what gives a relatively high cylinder pressure, quite a bit higher than a more conventional naturally aspirated engine from this time period, which is certainly not a 12:1 high RPM engine. Pre-ignition is a big concern with a 12:1 CR with port injection and the ionic current monitoring replacing conventional knock sensors is really impressive. I've not come across any info to suggest that pre-ignition is a problem and I agree that the wear pattern on the bearings do not appear to be related to pre-ignition.

The bearing wear is consistent with what has been established as oil starvation, it has been a while since I had looked into it since I don't think it makes sense to debate it as it has bene extensively discussed for years on other forums. It doesn't seem like there is much disagreement with that.

The cause for the excessive wear that some have seen MAY actually be caused by oil starvation at high RPM and NOT cold start. I don't know, but that certainly could be the reason for accelerated wear. I don't know if anyone has ever datalogged oil pressure and flow in the passage that supplies the oil to the crank. That would really help to establish whether there is sufficient flow and pressure.

Regarding the statements about ~25 micron clearances, 25 microns is 0.0009843". I think you were mixing SI and imperial units, but that is a big difference. The "optimal" clearance is ~0.0025" (63.5 microns) based on the 0.0010 per inch of journal diameter with an additional 0.0005 clearance.

I believe that BMW chose 10W60 for a very specific reason, I don't believe it was strictly related to cam phasers. I've never heard of this theory you mention but it may be true. 10W60 has very nice high temp sheer properties and this engine is a high revving engine with a short stroke. The piston speeds for such an design are very high and that generates a very high amount of heat. An oil that can provide adequate lubrication along the piston walls (alusil) and other parts of the valve train are critical.

The cam phasers are hydraulically actuated with a feedback loop. The camshaft sensors know precisely how much advance or retard has been delivered and will iteratively engage/disengage the vanos actuators to achieve the desired angle. The actuators feed the pressure to a double acting cylinder and there is a torsional spring to further assist with the return to the default position. The DME controls the logic for all of this. I don't disagree with the your contention that the cam phasers are garbage, but trying to solve flow issues with a thicker oil doesn't really jive. The fluidity of oil is correlated to its temperature, so at some point the oil will be too thin. All applications of variable valve timing utilize overlap in lieu of more traditional means to reduce NOx. BMW can simply adjust the parameters in the software to command the correct valve timing to pass emissions or even set the default cam lobe timing to meet the standards. Remember that in 2013 BMWNA authorised the use of LL4 oils in the 0W40 and 5W30 viscosities for the S85 and S65. They would never be able to do that if those oils could not maintain the necessary emissions requirements. CARB and the EPA would fine them and the cars wouldn't pass SMOG.

BMW and I disagree with your statement on mesh filters on the S85. There is an 80 micron stainless steel mesh filter that is nested in the block right where the outlet of the VANOS pump is. It looks like this (courtesy of FCP Euro). Part number 11367834525. The purpose of this filter is in fact to remove metal debris. The oil that has been sucked up by the main oil pump feeds the HP VANOS oil pump. None of that oil has been filtered through the remote oil filter (located in front of the passenger tire) before it goes to the actuators. The actuators have a 50 micron filter in front of it too.


934919
 

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I'm assuming any oil filter with those specifications would have to be a custom job? I'm only aware of the BMW oem and MAHN paper filters, and the K&P life time metal filter but only goes as low as 35 microns as advertised.

And with how sensitive the vanos system is on this car, cutting the oil flow rate with a more fine filter doesn't negatively impact the system at all?
The two best filter manufacturers for us are MANN and Mahle-Knecht. I believe BMW OEM is Mahle- Knecht. However even with the best filters, the problem still remains that the HP oil circuit feeding the VANOS is fed by oil that comes from the sump. The metal shavings (or chunks) that come from erroded bearings are flushed out of the rod bearing area straight into the sump and those suspended particles are then sucked up my the main oil pump which then feeds the VANOS oil pump.
 

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I'd further add that if 0W40 and 5W40/5W50 were insufficient to operate VANOS, I doubt that the VANOS quality tests will show that the it passed. I'm not just talking about the pass fail screen for valve quality, I'm talking about the other screens regarding min/max limits and adjustment time. I don't recall ever seeing anyone complain about how they went to a thinner oil and now the VANOS tests come back bad.
 

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25 microns (or yes, micrometers) is 0.001".

I agree on the VANOS performance with 0w40. I did run it in my car for ~5000mi on 0w40 without issue. I did try 5w50 on the next change and I did notice that the top end was quieter after warmed up with the 5w50, so I'm sticking with that. The screens are basically last chance screens, they get the big chunks out that really shouldn't be there to begin with. I need to look at the lube system diagram some more, I'd be surprised to see that the VANOS system was unfiltered, but I'll take your word for it. I stand by my comment on mesh filters, they generally have a beta ratio of only 2 at their mesh size. There is lots of info about this out there, so I'd suggest a read on that elsewhere.

As for bearing wear, they wear where the load is highest. Generally peak cylinder pressure is 12-16 degrees ATDC, obviously varies with load. I do not agree that ionic current is the best method of knock control. I would guess that the S85 started development in 2000/2001 (assuming ~5 year development cycle)...back then ionic current was en vogue for knock control. The acoustic knock systems I've worked with have been simply excellent, but we developed those in house. Some of the other stuff not so great.

The S65/85 engines are interesting. For the life of me I cannot understand why BMW ran 10w60 with those journal sizes/clearances. And this is coming from someone who typically uses 10 microns (0.0005") per inch of journal diameter. When I've mentioned running 10w60 to colleagues I generally get a look back like I just grew a dick out of my knee. I do have a friend that I meet up with every May that was let us say a senior development guy at BMW. It is interesting that he bought an E60 M5 to mess around with in his retirement. I suspect he worked on the program, but I'll find out and abuse him a corresponding amount. If I find out he had any bearing issues, I promise there will be no mercy shown!
 

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here is an interesting observation by Jim many moons ago:

"As for the thinner oil and bearings, I talked with the shop that is working a couple of crankshafts for me and they work with a high performance marine engine builder (who they would not name), but mentioned they had tended to run some extremely tight clearances on some engines and had attempted to run thinner oils to prolong life. To their surprise, thinner oils aggravated the wear and since switched to heavier oils with improved wear characteristics. This isn't much to go on, so I don't make much of it"

Custom Clevite Rod Bearings for S65/S85

Getting back to the S85 wear pattern on the top shell, with the claimed* tight bearing clearances i am surprised the damaged area is not elongated more spread over a larger area.
The idea being BMW's motive to set up bearings as "tight" is to increase the load capability of the bearings since the tighter the clearances the combustion impact forces are spread over a larger area of contact, while the looser the bearing the damaged area would be closer to a point contact.

Of course there are many other factors involved as always, I recall One of first owners that i had known personally of the high revving S-type 6 cylinder M3's lost the crank and rod bearings after a few stints at Gingerman, BMW gave him a new motor but instructed to only use their new at time 10-60 oil, a TSB to that effect followed.

It seems to me BMW was caught off guard on the frequency of loosing their early S-motor bearings, but the fact that 10-60 alleviated the problem; TSB's to use 10-60 oil came out for e39 as well .

I believe 10-60 was specified since for whatever reason it helped avoid loss of bearings inside warranty period.

I find it also interesting that no one has had worn bearings analysed to see weather the excessive wear is due to load limit of bearing shells have been exceeded, or if pattern is due to overheating due to insufficient cooling related to oil-flow rate or heating due to prolonged high rpm use.

* i do not recall much discussion on this but there was a claim by Troy back in 2014 that he found OEM rod big end bores to be oval and elongated thus effectively increasing bearing clearance right at the point where bearing experiences maximum combustion pressure.

This concerned me so much that i elected to join the s85 fold with an all new forged/billet bottom end motor with a 20% lighter reciprocating weight.



More food for thought.
 

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I generally agree with you. Regarding ionic current control, I'm also a bit speculative of how well it really works especially as the spark plugs wear. However there's enough evidence to show that pre ignition is not a problem in the S85. The fact that the PCM can command increasing amounts of spark advance and not trigger pre ignition simply by monitoring the voltage through the spark plug gap a production engine is really damn cool. I never said it was better than standard piezo knock sensors, but BMW seems to think that. It is interesting that the S65 does have conventional knock sensors and the S85 does not. I believe it was due to costs. I'd love to see how much SA you could get from the S85 with conventional piezos, it may be less which is why only their crown jewel engine had ionic feedback and nothing else did. If course that changes the entire control strategy of the S85, but whichever system could give more SA while staving off detonation would be the cheapest power mod by far.

Regarding the statements about 25 microns relating to this engine, I'm still unclear where that is coming from since you clearly know the difference in units. Your earlier posts about "...a ~25 micron clearance for the journal size". I fully agree that 10W60 would not be the right choice for an engine designed to have ~25 microns of clearance. Are you saying that BMW only meant to design in 25 microns of clearance? They way you referenced this doesn't seem to indicate that you meant 25 microns per inch of journal diameter.

There have been extensive teardowns and measurements of the bearing situation on S65 (rod and main bearings). The S85 and S65 are design dimensions are identical in that regard (I don't think there is disagreement on this point). When careful analysis was done on the the nominal dimensions along with some teardowns (I believe this was done by Van Dyne Engineering), they determined the nominal clearance BMW designed in to the engine is 0.00140" (35.56 microns). If they adhered to Mahle Clevite's white paper on bearing clearances, they should have designed in 0.00254" (64.52 microns) of clearance. I don't have reason to question the accuracy or recommendations of Van Dyne or Mahle Clevite. It seems that we agree that BMW's design clearance was questionable, especially when one considers the worst case situation of tolerance stackup, the clearances are far too small. The outcome is the failure mode that we see, which is accelerated bearing wear due to insufficient oil film thickness. The main bearings are also "under clearanced", there do not seem to be many S85 failures which makes sense given there is no radial force directed at the journal or the block, unlike what the rod bearing encounters via a point load coming from the rod. Further consider cold weather situations and the inherent lack of flow from a 10W60 at that temperature, and it is not hard to see why there have been extensive discussions on oil relating to bearing wear.

BMW has a habit of taking decades to resolve design deficiencies. The S54 and S62 also suffer from rod bearing wear also. I believe that BMW's thoughts on these clearances come directly from the fact that these engines were designed by the M division (all about Motorsport). Tight clearances are ideal for high performance "Motorsport" engines. They just stuck to their formulas and DID NOT properly consider tolerance stackups and standard deviation. We know that for the main bearings they gauged and fit specific bearings there. Apparently they did not gauge and fit rod bearings in the same manner. This explains why there are some engines that failed at very low mileage, and others that are just fine. Furthermore, it is quite common in the automotive world to have deviation approvals (read:exemptions) from certain corporate durability tests. These bearing failures are absolutely discoverable during the teardowns of engines subjected to durability testing in engine dyno cells. It makes sense to me that they installed a variable redline and stated the need to ensure a proper warm up procedure. I thought about installing a external oil pan heater element, but 0W40 is better for me.

The VANOS hydraulic schematic is out there in many places, but you can just look at how the main oil filter is routed to see that it is not a part of the VANOS circuit. It seems that alot of people that do the rod bearing job but don't inspect their VANOS and main oil pumps. I can see why, it is a bit of a pain and takes time to tear down. They also don't bother or even know about the mesh filter I mentioned. The only way to get to that filter is to remove the VANOS pump, which requires work to set the backlash when you put it back. Makes total sense. If you're not going to change the HP VANOS line, why bother even removing the VANOS pump? The answer is to inspect and change that filter. I'm happy to report that mine was free of any particles. Clearly it is not as good as a 20 micron synthetic media filter, but tighter filtration means decreased flow rate. BMW chose a 80 micron filter on purpose, it was to prevent larger sized pieces of junk from being sent upstream, a 20 micron filter would clog and have to be changed regularly.

I'm still interested in more info about the "garbage" cam phasers, you mentioned. Do you think the increased top end noise when you ran 0W40 was from the cam phasers? I mentioned before in my posts I run 0W40 only for its superior cold weather flow and I want faster oil flow in areas that have proven to suffer from oil starvation. My engine will not see much if any periods of sustained high RPM operation with 0W40.
 

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On the knock system, I think the state of the art on the acoustic method advanced sufficiently to outpace the earlier 'best system' that was ionic current (I'm speculating here).

Sorry to be confusing on the microns deal, all my posts microns were micrometers. I believe that 25 microns was the min possible clearance. Agree on the 0.0014"/35.5 micron number being nominal clearance value.

Why are the mains ok at the lower clearances as opposed to the rods? Basically there is a lot more oil flow to the mains as they are supplied first.

The cam phasers are not garbage from the perspective that you put x oil in and they work for the customer. edited They definitely are garbage though from the perspective that something that really shouldn't be driving the tribology in the rest of the engine is doing just that. edited For some time progressively thinner oils have been used to improve fuel economy, now a significant step to thicker viscosity oils is required for the cam phasers (BTW this is also the situation with Ford). From an engine development perspective I would consider this as a negative....obviously on balance it isn't though as they are used in the greater universe of the automobile industry. I do think it was the cam phasers that were more clattery, but hey, maybe it was the HLA's?
 

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The ionic sensing was invented and patented by Saab, It turned out to be dead reliable, in Car & Driver test reports the turbo Saabs always put down much better performance figures than competing turbo motors of greater advertised horsepower.

I believe this was by monitoring real time cylinder pressures there was no unwarranted preemptive timing pull back as in a knock sensor only motor.

BMW mentioned that the reason for going with ionic sensing was that in the range of 6000 to 8200 rpm the s85 had too much mechanical noise for reliable knock sensor operation.
 

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Toyota's 2007 Tundra 5.7 L cam phasing technology worked flawlessly with the specified energy saving 0-20 oil even in the summer heat
The fact the 5.7 L is a 6000 rpm motor with low valve spring pressure of course helps
 

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Also Japanese vendors of phasers! Believe it or not, the valvetrain 'stab' torques (due to each valve event) are worse at low engine speeds. I would think that this would work the valvedrive (including phasers) harder on the S85 as it does on any other engine.

The thing with acoustic knock sensors is that you have to be able to, yes, characterize the noise of the engine accurately. I can tell you that it is done on engines that are a lot noisier and higher revving than the S85.

While I have certainly measured ionic current experimentally in the test cell, I have no real experience using it as a means of knock control. I do understand it to be reliable though.
 

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here is an interesting observation by Jim many moons ago:

"As for the thinner oil and bearings, I talked with the shop that is working a couple of crankshafts for me and they work with a high performance marine engine builder (who they would not name), but mentioned they had tended to run some extremely tight clearances on some engines and had attempted to run thinner oils to prolong life. To their surprise, thinner oils aggravated the wear and since switched to heavier oils with improved wear characteristics. This isn't much to go on, so I don't make much of it"

Custom Clevite Rod Bearings for S65/S85

Getting back to the S85 wear pattern on the top shell, with the claimed* tight bearing clearances i am surprised the damaged area is not elongated more spread over a larger area.
The idea being BMW's motive to set up bearings as "tight" is to increase the load capability of the bearings since the tighter the clearances the combustion impact forces are spread over a larger area of contact, while the looser the bearing the damaged area would be closer to a point contact.

Of course there are many other factors involved as always, I recall One of first owners that i had known personally of the high revving S-type 6 cylinder M3's lost the crank and rod bearings after a few stints at Gingerman, BMW gave him a new motor but instructed to only use their new at time 10-60 oil, a TSB to that effect followed.

It seems to me BMW was caught off guard on the frequency of loosing their early S-motor bearings, but the fact that 10-60 alleviated the problem; TSB's to use 10-60 oil came out for e39 as well .

I believe 10-60 was specified since for whatever reason it helped avoid loss of bearings inside warranty period.

I find it also interesting that no one has had worn bearings analysed to see weather the excessive wear is due to load limit of bearing shells have been exceeded, or if pattern is due to overheating due to insufficient cooling related to oil-flow rate or heating due to prolonged high rpm use.

* i do not recall much discussion on this but there was a claim by Troy back in 2014 that he found OEM rod big end bores to be oval and elongated thus effectively increasing bearing clearance right at the point where bearing experiences maximum combustion pressure.

This concerned me so much that i elected to join the s85 fold with an all new forged/billet bottom end motor with a 20% lighter reciprocating weight.

More food for thought.
Gingerman! Fond memories a few times back when I used to work at Ford. Kinda of a small pathetic track, but many of us track guys got our jollies off at work at the proving grounds. I remember going there with my boss who had a red E36 M3 and John Heinricy was there with a bunch of his guys with a C4 Z06, they seemed to be doing driver development. GM had alot of "can't do it on company property stuff back then". I remember my boss had just reinforced the rear strut towers and John was quite interested in it. Funny (actually not) how the E46s also had even more serious major rear body structure issues. I also had been thinking about E46 M3 too for over 10 years, but failures in the rear body structure are just unacceptable and hard to really fix. I'm glad that the M5s have not had issues like that. I've been looking to get an e39 M5 for close to 10 years and never did it because of all the issues. Prices never seemed to dip below 15k for ones that had reasonable miles and good condition. I always thought that they were a bit overpriced. It's funny that I ended up with a few e60 M5s, which I think have more problems overall, but all seem to be fixable but it's reputation has been earned.
 

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Why are the mains ok at the lower clearances as opposed to the rods? Basically there is a lot more oil flow to the mains as they are supplied first.
I've not come across much in the way of S85 main bearing failures, but have seen a few instances of failures on the S65 on the other forum. While I'm inclined to agree that there is a lot more oil flow to the mains, I have some theories of how that could be a contributor to the rod bearing issues on the respective engines. There are several instances of seized and overheated rod bearings on the S65. There should be more main bearing failures on the S85. I don't think that the fact that M3 guys are more active posters explains the difference. One instance in particular the OP never indicated what the root cause was, but he had BE bearings installed and they failed a short time after. It could have been inadequate side clearance so both bearings on the same journal simply overheated, but it also could have been blockage of oil flow at main bearing which cut off flow downstream. He said he was going to have it torn down but I don't remember seeing him report back.

The pictures of S65 main bearings are not pleasing as far as wear. We don't see many S85 pictures because very few people here are pulling their engines and removing the bed plate to replace the mains. I really don't care for the harder bearing material the BMW phased in in 2009 to eliminate lead. I'm also damn curious, but this is a new can of worms and I don't have the tools to put it back together. I've toyed with the idea of tearing down my spare 2010 S85 but have never disassemble a glued together bedplate design like what we have with the S65 and S85. Two of the handful of guys that have done this are Troy and Jim Colley. I'm not sure if they farm out the line boring work. Maybe this is a seperate thread. But curious to know if anyone has insight or experience with this.

My theory on main bearing is this-it is only a theory, I don't have the means to instrument a test: In the main bearing, there is a channel and hole that allow the oil to flow in and around the bearing surface. That hole is an orifice, which will affect the flow and pressure down stream. This is simple fluid dynamics. If that orifice is too large, flow increases, but pressure decreases. That decrease in pressure may lead to insufficient oil pressure at the rod bearings to build up the hydrodynamic layer at cold start but depending on the pressure (and flow) the oil starvation may continue beyond cold start. If the main bearing ever spins out of position, then the hole is no longer in the correct position and everything down stream will be starved. I believe the main bearings are the same design between the S85 and S65, but obviously the oil pump designs are different and the lube circuit for the S85 is a bit bigger due to the extra cylinders. There could be noteworthy pressure differences at the rod journal between the two engines that explain some of the differences in wear/oil starvation that are compounded by inadequate rod bearing clearances.
 
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