Scary rod bearing thread s85

[Longwong]

Well perhaps it will pay off that I have driven my car from day 1 (broke it in 500 miles) like a race car. Redlining, lowest gear possible, working out the engine as hard as I can on the freeway, lots of 3rd gear pulls and 4th gear on the freeway. Always have engine temps up and revs pushing 8k many many times a drive. Perhaps since I did this from the beginning I have kept the oil at proper viscosity and thin enough it did a good job.

Seems on cold start or not driving it hard/keeping oil temps too low would cause the most problems as the thick oil would not lubricate

Seems the answer is too drive the car harder and keep the engine temps up so the oil is nice and thin

[Gearhead999s]

Interesting read here about bearings in Nascar V8's that run to 9600 rpm and produce 900 bhp.They are running tighter clearances now than they used to.

http://www.precisionenginetech.com/t...g-tech-part-1/

[Transfer]

Originally Posted by Longwong

Well perhaps it will pay off that I have driven my car from day 1 (broke it in 500 miles) like a race car. Redlining, lowest gear possible, working out the engine as hard as I can on the freeway, lots of 3rd gear pulls and 4th gear on the freeway. Always have engine temps up and revs pushing 8k many many times a drive. Perhaps since I did this from the beginning I have kept the oil at proper viscosity and thin enough it did a good job.

Seems on cold start or not driving it hard/keeping oil temps too low would cause the most problems as the thick oil would not lubricate

Seems the answer is too drive the car harder and keep the engine temps up so the oil is nice and thin

Multi grade oil gets thicker (higher SAE viscosity) as you reach full operating temp, not thinner.

[Longwong]

Um no. Cold oil is thicker than hot oil. The first number is the viscosity rating when cold and the second when it is hot. It does not get thicker. Hence the entire reason you need to warm up the oil and engine to get the oil flowing. Its common sense. take a bottle of oil and pour it at 0 degrees and than 100 degrees and tell me which oil is thinner or less viscous may be the proper term

[V8FunNaturally]

There are two schools of engine design. The first school is from racing with the experience of pushing engines to their limits, using reverse failure analysis and an intuitive understanding of design compromises. The second is based on computer simulations to model and solve the elastohydrodynamic problem. In reality manufacturer use a combination of both but in some cases where there is no precedence they will rely overly on simulation to push the curve of what had been done previously. Models used in simulation softwares like AVL EXCITE combines the elastic and inertial properties of the crankshaft, the flexibility of the crankshaft and block, and the elastohydrodynamic lubrication and asperity contact nature of the journal-bearing systems.

Tribology is not my field of expertise but reading some recent articles on the topic the key for a realistic simulation that can reveal problems is the copulation between the elastohydrodynamic lubrication model and the flexible structure motion models (both large rigid-body motion and small elastic deformation). The flexibilities of crankshaft and block can dramatically affect elastohydrodynamic performance of bearings, the elastics of journal-bearing system can not be ignored in rigorous bearing hydrodynamic lubrication analysis. From these simulations a couple of BMW engineers had to decide on a clearance for the slide bearings. Apparently, they had sufficient confidence in the simulation tool to ignore Mahle-Clevite -The bearings manufacturer- recommendations and deviate significantly from safe clearance numbers.
Extensive computer simulation is only as good as the underlying models used to simulate what is happening in real. How much pre production life-limit testing was done by BMW on the S85 and S65 block under load ? I am guessing not more than 100,000 equivalent miles and probably on only a couple of blocks.
These engineers or someone who know them are probably reading this thread.

For the interested reader here is a peak at the AVL EXCITE simulation tool that would be used by BMW to simulate this (or a similar software).



The elastohydrodynamic contact solutions of AVL EXCITE
provide realistic results for slider bearing and piston-liner
contacts like minimum oil film thickness and pressure
distributions etc. Typical applications are listed as follows.
Elastohydrodynamic bearing analysis:
• determination of accurate bearing characteristic
• assessment of split line position and crush relief
• assessment of oil supply layout and oil flow
• reduction of hydrodynamic / mixed friction, wear
prediction
• support of slipping and fretting analysis of bearing
shells and in split-line
• support of investigating damage and cavitation
• support of noise optimization

[kawasaki00]

If we went off simulation we would have multiple engines out of the race every week. The problem with some of that stuff is everyone wants to try and re-invent the wheel, somethings just have to be... like having enough bearing clearance. Lets not forget how bad they screwed up the e46 bearing deal and they did it again on the next generaton car. Of course it is not the same extint as the e46 but they still muffed it up. The only way a rod bearing should come out of a engine is because there is no oil in it. Even too much timing will not beat rod bearings out like that. Beat the pin bores out but not rod bearings. Problem with todays society is too many things are built off computer models and not so much common knowledge.

[urBan_dK]

Originally Posted by Obioban

https://www.google.com/search?q=s200...oe=UTF-8&hl=en

The burden of proof is on you to back up your claim that the S2000 has rod bearing issues resulting from design issues. Any car can have a rod bearing go from oil starvation.

[aussiem3]

How will one know there is a bearing issue prior to a catastrophic failure? I am no expert and I drive the car listening out for the odd noise. There is so much happening inside the hood it's very difficult to say what noise is coming from where.

From what I read is that an interim solution is that don't push the car until the oil temperature has reached the optimum for operations ... needle close to 12 o'clock as possible. Oh boy ... what a dilemma!

[Gearhead999s]

Originally Posted by aussiem3

How will one know there is a bearing issue prior to a catastrophic failure? I am no expert and I drive the car listening out for the odd noise. There is so much happening inside the hood it's very difficult to say what noise is coming from where.

From what I read is that an interim solution is that don't push the car until the oil temperature has reached the optimum for operations ... needle close to 12 o'clock as possible. Oh boy ... what a dilemma!

That's common sense to keep revs & load down till your oil temps are up to normal operating temps.But the again I grew up around round engines in aircraft

[aussiem3]

Originally Posted by Gearhead999s

That's common sense to keep revs & load down till your oil temps are up to normal operating temps.But the again I grew up around round engines in aircraft

That's how I have driven the car from day one ... waiting for the optimum temp before even topping 5k rpm. I am glad that I have driven like that given this ugly issue of bearing failures. I just wish there is a solution from BMW. I will contact BMW in Australia and ask them what their stand is in case of a bearing failure ... hope I don't get answer like "it's a consumable and it's like all other wear and tear ..."

[Transfer]

Originally Posted by Longwong

Um no. Cold oil is thicker than hot oil. The first number is the viscosity rating when cold and the second when it is hot. It does not get thicker. Hence the entire reason you need to warm up the oil and engine to get the oil flowing. Its common sense. take a bottle of oil and pour it at 0 degrees and than 100 degrees and tell me which oil is thinner or less viscous may be the proper term

Ok, then someone edumacate me. 10w-60 means SAE viscosity of "10" when cold, right? and "60" when at temp, right? soooo, what am I doing wrong here?

[///M Power-Belgium]

Originally Posted by aussiem3

That's how I have driven the car from day one ... waiting for the optimum temp before even topping 5k rpm. I am glad that I have driven like that given this ugly issue of bearing failures. I just wish there is a solution from BMW. I will contact BMW in Australia and ask them what their stand is in case of a bearing failure ... hope I don't get answer like "it's a consumable and it's like all other wear and tear ..."

Now my friend, i'm curious to heare what answer you will get ?
And i hope for all of us...that this answer will be...pos.+

[kawasaki00]

Originally Posted by Transfer

Ok, then someone edumacate me. 10w-60 means SAE viscosity of "10" when cold, right? and "60" when at temp, right? soooo, what am I doing wrong here?

http://www.upmpg.com/tech_articles/motoroil_viscosity/

This explains it.
For this problem we have if there were a 5w-60 that would be the ultimate for us. Unfortunately there is no such grade. The 5w would help a ton at start up but still protect like a 60 weight at temp. This is why the rotella 5-40 is a trade off. It is better at low temps and flows better but the untimate high temp shear strength is not as much as a 60.
The second number is the protection factor not the weight. A 10w-30 and a 10w 60 is till the same weight at cold temp.

[Gearhead999s]

Originally Posted by aussiem3

That's how I have driven the car from day one ... waiting for the optimum temp before even topping 5k rpm. I am glad that I have driven like that given this ugly issue of bearing failures. I just wish there is a solution from BMW. I will contact BMW in Australia and ask them what their stand is in case of a bearing failure ... hope I don't get answer like "it's a consumable and it's like all other wear and tear ..."

I use 3000 till I see about 90c.It is a pain when I hop on the highway and the traffic is running 120 kph +.

[V8FunNaturally]

Originally Posted by kawasaki00

If we went off simulation we would have multiple engines out of the race every week. The problem with some of that stuff is everyone wants to try and re-invent the wheel, somethings just have to be... like having enough bearing clearance. Lets not forget how bad they screwed up the e46 bearing deal and they did it again on the next generaton car. Of course it is not the same extint as the e46 but they still muffed it up. The only way a rod bearing should come out of a engine is because there is no oil in it. Even too much timing will not beat rod bearings out like that. Beat the pin bores out but not rod bearings. Problem with todays society is too many things are built off computer models and not so much common knowledge.

I have a problem believing that they simply mindlessly and foolishly mis-designed the clearance on the bearings. I cannot believe that one individual engineer at BMW just said "screw common sense, I am going to design this with no margin at all". This had to be scrutinized, reviewed and decided by the whole group unless they let one star senior individual fool the whole arena. Why would they screw something so obvious there had to be something positive to go opposite from accepted practices. The HP gain isn't significant, the noise reduction cannot justify a reliability risk, the volume of the oil pump is not significantly reduced by the tighter clearance. So why ? There had to be something really positive in it for them to justify it. All I can be sure of at the end of the day is they are trying to make a profit, not repeat mistakes.

[Transfer]

Originally Posted by kawasaki00

http://www.upmpg.com/tech_articles/motoroil_viscosity/

This explains it.
For this problem we have if there were a 5w-60 that would be the ultimate for us. Unfortunately there is no such grade. The 5w would help a ton at start up but still protect like a 60 weight at temp. This is why the rotella 5-40 is a trade off. It is better at low temps and flows better but the untimate high temp shear strength is not as much as a 60.
The second number is the protection factor not the weight. A 10w-30 and a 10w 60 is till the same weight at cold temp.

Thank you. I had it slightly twisted.
I was on the fence, but now I'm glad I had Benvo code in the lower warm up RPM range when he did all my other coding/tuning. Thanks Mike

[BPMSport]

Originally Posted by Transfer

Thank you. I had it slightly twisted.
I was on the fence, but now I'm glad I had Benvo code in the lower warm up RPM range when he did all my other coding/tuning. Thanks Mike

My pleasure. We recognize the importance of keeping RPM's low when the engine is cold. We believe that the factory 6,500 RPM limit on cold start is way too aggressive and could induce premature wear or damage on engine internals.

So for that reason we suggest the cold start rev limit reduction to those that use our performance software.

Better safe than sorry!

[aussiem3]

Originally Posted by Transfer

... but now I'm glad I had Benvo code in the lower warm up RPM range when he did all my other coding/tuning. Thanks Mike

Same here ... Thank you Mike Benvo

[Obioban]

Originally Posted by sunsweet

I have a problem believing that they simply mindlessly and foolishly mis-designed the clearance on the bearings. I cannot believe that one individual engineer at BMW just said "screw common sense, I am going to design this with no margin at all". This had to be scrutinized, reviewed and decided by the whole group unless they let one star senior individual fool the whole arena. Why would they screw something so obvious there had to be something positive to go opposite from accepted practices. The HP gain isn't significant, the noise reduction cannot justify a reliability risk, the volume of the oil pump is not significantly reduced by the tighter clearance. So why ? There had to be something really positive in it for them to justify it. All I can be sure of at the end of the day is they are trying to make a profit, not repeat mistakes.

Agreed.

Also, worth noting that the s54 bearing issue was not a design issue but a manufacturing fault by the bearing company. They didn't redesign them, the had a recall and put in bearings that were actually made to their spec.

[DFDubM]

Originally Posted by sunsweet

I have a problem believing that they simply mindlessly and foolishly mis-designed the clearance on the bearings. I cannot believe that one individual engineer at BMW just said "screw common sense, I am going to design this with no margin at all". This had to be scrutinized, reviewed and decided by the whole group unless they let one star senior individual fool the whole arena. Why would they screw something so obvious there had to be something positive to go opposite from accepted practices. The HP gain isn't significant, the noise reduction cannot justify a reliability risk, the volume of the oil pump is not significantly reduced by the tighter clearance. So why ? There had to be something really positive in it for them to justify it. All I can be sure of at the end of the day is they are trying to make a profit, not repeat mistakes.

I'm certainly not an engineer but this is exactly what I've been thinking. Those of you who are engineers or who know about such things, what is the trade-off or advantage to reducing clearance?

[BPMSport]

I'm no engine building engineer - but to my understanding:

1: A smaller clearance will more evenly spread the load across the surface of the bearing, and will keep pressure across the bearing more consistent

2: A smaller clearance will decrease the amount of oil that is necessary to properly lubricate between the bearing and crankshaft

Now this is given that the oil viscosity is low enough to support the thinner clearance. If the oil is too think, then it's not going to lubricate properly.

3. Having tighter clearances reduces the amount of oil pressure needed to effectively lubricate those parts.

4: Tighter clearances can increase oil temperature and also increase bearing temperature.

5: On higher HP applications there might be a slight advantage to running slightly wider clearances to prevent distortion.

I will definitely defer to the engine experts on these points. Hope this helps somewhat.

[VCMpower]

I am such a procrastinator Good job Mike!

Originally Posted by Mike Benvo

My pleasure. We recognize the importance of keeping RPM's low when the engine is cold. We believe that the factory 6,500 RPM limit on cold start is way too aggressive and could induce premature wear or damage on engine internals.

So for that reason we suggest the cold start rev limit reduction to those that use our performance software.

Better safe than sorry!