[F87source]

Originally Posted by M-Pilot

Yup, exactly! Tony from VTT also says it's more RPM related:

Originally Posted by doughboy

Looking logically, a sudden increase in (clockwise) crank rpm would place a strong anticlockwise (ie undo right hand thread) force on the hub. Conversley a sudden decrease in rpm would apply force to tighten the hub. This may go some way to explaining the slipping on it money shifts and kickdowns.

I just wanted to also bring this up and some more thoughts I had on the issue being RPM related.

1) I think this issue is more prevalent on the S55 because there is more stuff running off of the timing chain, i.e. mechanical water pump, and more indirectly the dual HPFP's running off the cam lobe which is also related to the timing system, this means alot more intertia is present in the timing assembly when it is rotating. This means that the rapid RPM changes from down shifting or up shifting puts more torque on the friction disc because the whole timing system has more inertia. A counter clockwise torque would be worse because it would loosen the hub, which is evident in down shifts when rpms jump and the crank spins faster clock wise meaning a counter clockwise torque is applied while trying to accelerate the rest of the timing chain components.

2) More horse power leads to faster revving which could also be a cause in spinning the hub. So this is why you see it more on high horse power cars.

3) DCT shifts extremely harshly and quickly leading to rapid rpm changes.


A non RPM related issue would be the bolt vibrating loose over time. Could this be the harmonic dampener not being as good (I saw this posted a few pages before and this is really a food for thought moment), because vibrating the crank bolt loose doesn't seem to happen on n54's and n55's even super high mileage examples.




All of these issues are infinitely more prevalent on the S55 vs. N54's and N55's which almost never experience these issues (by almost never it might as well be never since they literally do not experience these issues with the exception being the really rare super high horse power N54's). So this is why I think my reasons above are likely probable as the S55 engine has more running off the timing system, makes more power easier than most of the n55 and n54 cars, has the dct.

[Megator]

Originally Posted by F87source

I just wanted to also bring this up and some more thoughts I had on the issue being RPM related.

1) I think this issue is more prevalent on the S55 because there is more stuff running off of the timing chain, i.e. mechanical water pump, and more indirectly the dual HPFP's running off the cam lobe which is also related to the timing system, this means alot more intertia is present in the timing assembly when it is rotating. This means that the rapid RPM changes from down shifting or up shifting puts more torque on the friction disc because the whole timing system has more inertia. A counter clockwise torque would be worse because it would loosen the hub, which is evident in down shifts when rpms jump and the crank spins faster clock wise meaning a counter clockwise torque is applied while trying to accelerate the rest of the timing chain components.

2) More horse power leads to faster revving which could also be a cause in spinning the hub. So this is why you see it more on high horse power cars.

3) DCT shifts extremely harshly and quickly leading to rapid rpm changes.


A non RPM related issue would be the bolt vibrating loose over time. Could this be the harmonic dampener not being as good (I saw this posted a few pages before and this is really a food for thought moment), because vibrating the crank bolt loose doesn't seem to happen on n54's and n55's even super high mileage examples.




All of these issues are infinitely more prevalent on the S55 vs. N54's and N55's which almost never experience these issues (by almost never it might as well be never since they literally do not experience these issues with the exception being the really rare super high horse power N54's). So this is why I think my reasons above are likely probable as the S55 engine has more running off the timing system, makes more power easier than most of the n55 and n54 cars, has the dct.

I have come to much the same conclusion.

I think failure is due to "luck" or standard distribution. The joint is designed to exert "at least" X clamping load but due to small variations some joints fall under X. These joints are the ones that fail when overloaded.

Maybe not common knowledge but torquing up bolted joints is more like "alchemy" than an exact science. The final force exerted by the bolt can varry quite a bit. OFC this can be controlled to quite tight margins but that comes at a cost and complexity that cannot always be reproduced.

If it was the bolt backing out then threadlocker, a finer thread, or more engagement should cure the problem. If its harmonics then balancing should have fixed things.

Instead BMW changed the washer, which makes me thing they where trying to up the X clamping load thereby moving the failure distribution curve so 0/less cars fail.

Edit: Clamping load is a bit of a misnomer, I mean the frictional force between the various components that are otherwise free to spin with respect to each other. This is a function of the clamping load and friction coef and area between the parts.

[F87source]

Originally Posted by Megator

I have come to much the same conclusion.

I think failure is due to "luck" or standard distribution. The joint is designed to exert "at least" X clamping load but due to small variations some joints fall under X. These joints are the ones that fail when overloaded.

Maybe not common knowledge but torquing up bolted joints is more like "alchemy" than an exact science. The final force exerted by the bolt can varry quite a bit. OFC this can be controlled to quite tight margins but that comes at a cost and complexity that cannot always be reproduced.

If it was the bolt backing out then threadlocker, a finer thread, or more engagement should cure the problem. If its harmonics then balancing should have fixed things.

Instead BMW changed the washer, which makes me thing they where trying to up the X clamping load thereby moving the failure distribution curve so 0/less cars fail.

Edit: Clamping load is a bit of a misnomer, I mean the frictional force between the various components that are otherwise free to spin with respect to each other. This is a function of the clamping load and friction coef and area between the parts.

Yeah I agree.

However I would not use thread locker on the crank bolt, if you ever have to remove it because the hub itself slipped from breaking friction and not the bolt itself vibrating loose you will be in a huge amount of trouble. The hub is already torqued with a giant bar, imagine breaking that loose with thread locker.

[doughboy]

Originally Posted by Thescout13

Gotta love the British (assuming you are since from the UK, but apologies if you're a Scot or Welsh) and their concise use of language to get right at the point.

Haha, sometimes blunt is good...

BTW, Scots and Welsh are British too, I'm English so British also, and thus not bothered what Scots and Welsh think..... We love to hate each other, kind of like siblings that have been fighting for 1500+ years

[F87source]

Originally Posted by doughboy

Haha, sometimes blunt is good...

BTW, Scots and Welsh are British too, I'm English so British also, and thus not bothered what Scots and Welsh think..... We love to hate each other, kind of like siblings that have been fighting for 1500+ years

Lol

[Got f1?]

Great points, thanks for sharing them.

[F87source]

Originally Posted by Got f1?

Great points, thanks for sharing them.

No problem!

Since you have an M2C I recommend getting a VTT CBC on black friday this year when they have really good sales.

I managed to get an even better than black friday deal (30% off) earlier this year when VTT had a forum sale so that was really nice.

[Megator]

Originally Posted by F87source

No problem!

Since you have an M2C I recommend getting a VTT CBC on black friday this year when they have really good sales.

I managed to get an even better than black friday deal (30% off) earlier this year when VTT had a forum sale so that was really nice.

Meh not sure the CBC is a good idea/worth it. There is at least one in DE that failed. A German tuner in the thread blamed it on being an ebay special tho...

Like I said, your either good or your not. CBC wont help with that as it is just another anti bolt backing out solution.

[F87source]

Originally Posted by Megator

Meh not sure the CBC is a good idea/worth it. There is at least one in DE that failed. A German tuner in the thread blamed it on being an ebay special tho...

Like I said, your either good or your not. CBC wont help with that as it is just another anti bolt backing out solution.

The CBC will deal with 1/2 of the issue which is the bolt backing out due to vibrations, it is not a complete solution since the friction disk can still slip but it is better than nothing.


Likely the one that failed just has the hub break friction and spin.


IMO $99 to prevent 1/2 of the hub issue is pretty worth it to me, especially since I got it for 30% off.

[Megator]

Originally Posted by F87source

The CBC will deal with 1/2 of the issue which is the bolt backing out due to vibrations, it is not a complete solution since the friction disk can still slip but it is better than nothing.


Likely the one that failed just has the hub break friction and spin.


IMO $99 to prevent 1/2 of the hub issue is pretty worth it to me, especially since I got it for 30% off.

Well we dont know if it is "half the issue" as discussed above. Once the hub spins the preload on the bolt is gone so it can back out. To me the bolt backing out is not a root cause of the failure but a symptom of it.

Maybe a CBC stops the bolt from backing out more and the timing getting messed up even more. For the German guy it did not work out that way.

Also instal costs are way more than the cheap aluminium part and bolt cost. Depending on your shops rate this could be several hundred dollars to instal.

There is also the fact that you added weight to the nose of the crank. People forget that cranks are also balanced fore to aft and that an imbalance along the crank can cause a crank to fail. I have seen it with my own two eyes on a poorly made crank that had a fatigue crack running accross a 10cm dia rod bearing journal.

So my 2 cents. Put the 500-1k of the CBC instal costs into Tesla stock and hope you get SPCH before the bubble bursts.

[F87source]

Originally Posted by Megator

Well we dont know if it is "half the issue" as discussed above. Once the hub spins the preload on the bolt is gone so it can back out. To me the bolt backing out is not a root cause of the failure but a symptom of it.

It has to be the friction being broken if the CBC is working properly, and it should since it is a retention device preventing the bolt from backing out.

Not true, the hub is unthreaded so if it spins the bolt will remain tight since it is threaded onto the crank extremely tightly and not the hub, and the CBC is holding that in preventing it from backing out. Even in normal cases if the hub spins the bolt stays put. So all the preload is between the bolt and the crank snout.

The bolt backing out is due to vibrations.

The hub spinning is due to counter clockwise torque from RPM changes - acting Kind of like an impact gun or the hub can also spin if the bolt comes loose.

Originally Posted by Megator

Maybe a CBC stops the bolt from backing out more and the timing getting messed up even more. For the German guy it did not work out that way.

Like I said before you can have these scenarios:

1) Hub spins bolt does not back out, if it spins bad enough you will jump alot of timing and boom engine damage. If it spins but not too bad then the crank position sensor will catch it and limp mode the car saving the motor.

2) bolt backs out, sometimes the car can catch it and limp the car but it can be all or nothing and you get catastrophic engine damage.

CBC solves issue 2, German guy likely had issue 1.

Originally Posted by Megator

Also instal costs are way more than the cheap aluminium part and bolt cost. Depending on your shops rate this could be several hundred dollars to instal.

Intall it yourself problem solved. It is a fairly easy task.

Originally Posted by Megator

There is also the fact that you added weight to the nose of the crank. People forget that cranks are also balanced fore to aft and that an imbalance along the crank can cause a crank to fail. I have seen it with my own two eyes on a poorly made crank that had a fatigue crack running accross a 10cm dia rod bearing journal.

Incorrect people did not forget that fact. I was extremely worried about this issue and spoke to alot of engineers from both VTT, litchfield, and the lexus RCF and ISF community (more on this later) before I pulled the trigger on this.

Yes it is true the crank is carefully balanced and if it were off balanced catasrophic engine damage would occur.

BUT the CBC is a perfectly symmetrical object that bolts right on the central axis of the crank and weighs very very little, like 30 grams. Since it is symmetrical and weighs so little and bolted to the middle axis of the rotating crank balance is a non issue.

Individuals run lightened harmonic dampeners all the time with no issue, people in the lexus RCF community run aluminium drive ring add ons (adds quite a bit of weight) to the damper for supercharger belts without issue because it is balanced and on the central axis of rotation.

Also the crank is balanced via the counter weights, the dampener does not really contribute to that, it contributes to vibration dampening. Since the I6 engines are inheriently quite well balanced and since the crank has substantial counter weights and weighs in at a total of 20kg+ I believe the BMW engine is internally balanced. This means the flywheel and harmonic balancer is not part of the balancing process of the crank and the damper is only there for vibration dampening purposes. https://help.summitracing.com/app/an...ine-balance%3F
Alternatively if the engine were not internally balanced people who run different mass fly wheels or dampers would be screwed, and since that is not that case it is extremely probable that the engine is internally balanced.


so as long as the CBC is balanced and light it should be fine and not add any more vibrations to the crank (and since the CBC is symmetrical and bolted on axis of rotation it is fine). Also the CBC is 30 grams, if you get dirt and debris build up on the damper over time that would weigh more than the CBC, and dirt doesn't seem to throw the crank off. I've seen some dampers caked in dirt that defintely added weight to the damper without issue.

Originally Posted by Megator

So my 2 cents. Put the 500-1k of the CBC instal costs into Tesla stock and hope you get SPCH before the bubble bursts.

LOL

the only issue is that if the failure is catastrophic and costs $22K the return on the stocks wouldn't be enough.

[Megator]

Originally Posted by F87source

It has to be the friction being broken if the CBC is working properly, and it should since it is a retention device preventing the bolt from backing out.

Not true, the hub is unthreaded so if it spins the bolt will remain tight since it is threaded onto the crank extremely tightly and not the hub, and the CBC is holding that in preventing it from backing out. Even in normal cases if the hub spins the bolt stays put. So all the preload is between the bolt and the crank snout.

The bolt backing out is due to vibrations.

The hub spinning is due to counter clockwise torque from RPM changes - acting Kind of like an impact gun or the hub can also spin if the bolt comes loose.


Like I said before you can have these scenarios:

1) Hub spins bolt does not back out, if it spins bad enough you will jump alot of timing and boom engine damage. If it spins but not too bad then the crank position sensor will catch it and limp mode the car saving the motor.

2) bolt backs out, sometimes the car can catch it and limp the car but it can be all or nothing and you get catastrophic engine damage.

CBC solves issue 2, German guy likely had issue 1.


Intall it yourself problem solved. It is a fairly easy task.


Incorrect people did not forget that fact. I was extremely worried about this issue and spoke to alot of engineers from both VTT, litchfield, and the lexus RCF and ISF community (more on this later) before I pulled the trigger on this.

Yes it is true the crank is carefully balanced and if it were off balanced catasrophic engine damage would occur.

BUT the CBC is a perfectly symmetrical object that bolts right on the central axis of the crank and weighs very very little, like 30 grams. Since it is symmetrical and weighs so little and bolted to the middle axis of the rotating crank balance is a non issue.

Individuals run lightened harmonic dampeners all the time with no issue, people in the lexus RCF community run aluminium drive ring add ons (adds quite a bit of weight) to the damper for supercharger belts without issue because it is balanced and on the central axis of rotation.

Also the crank is balanced via the counter weights, the dampener does not really contribute to that, it contributes to vibration dampening. Since the I6 engines are inheriently quite well balanced and since the crank has substantial counter weights and weighs in at a total of 20kg+ I believe the BMW engine is internally balanced. This means the flywheel and harmonic balancer is not part of the balancing process of the crank and the damper is only there for vibration dampening purposes. https://help.summitracing.com/app/an...ine-balance%3F
Alternatively if the engine were not internally balanced people who run different mass fly wheels or dampers would be screwed, and since that is not that case it is extremely probable that the engine is internally balanced.


so as long as the CBC is balanced and light it should be fine and not add any more vibrations to the crank (and since the CBC is symmetrical and bolted on axis of rotation it is fine). Also the CBC is 30 grams, if you get dirt and debris build up on the damper over time that would weigh more than the CBC, and dirt doesn't seem to throw the crank off. I've seen some dampers caked in dirt that defintely added weight to the damper without issue.



LOL

the only issue is that if the failure is catastrophic and costs $22K the return on the stocks wouldn't be enough.

You are missunderstanding two fundamental issues

1) When you tighten a bolt it is the "free" part of the bolt which is elastically deformed (ie the distance between the bottom of the head which in this case rests on the hub and the end of the thread engament in this case where it threads into the crank) and therby the bolt exerts a preload on all the sandwiched components.

To put it another way you are stretching 9.8mm of "free" bolt length to 10mm (the thickness of the components being sandwiched). The bolt wants to be 9.8mm long, so it pulls everything together. It is esentially a stretched out spring clamping everything together. Just like a spring its force is proportional to the amount of stretch from its resting position.

When the hub spins then the length of the assembly also changes by a miniscule amount. So the bolt is no longer stretched to 10mm but 9.9mm. This results in a loss of preload without the bolt spinning or changing position with respect to the crank.

Easy backyard mechanic test. Take a bolt and nut and sandwich something between them you can remove once they are tight (like a U shaped washer). Now remove the between component and the nut and bolt are free to rotate with respect to each other again. Esentially this is what happens with SCH

CBC does nothing in this regard.

Once the preload is gone/reduced, the threads of the bolt no longer exert the same force on the threads of the crank and the bolt is free to back out.

But the damage was already done! You just get into a spiral where less preload = more SCH/ bolt backing out = even less preload = even more SCH/bolt backing out.

The way you explain it does not work. If the preload in the bolt was built solely between the bolt and crank then you could never ever in a 1000 years apply preload to the crank hub components.

The numbers are obv. made up and just to illustrate a point.

So to me your point 1 is the failure mode and point 2 is a symptom of the failure not a cause.


2) I am not talking about the rotational balance of the crank. I am talking about the balance from the front to the rear.

I dont know how better to transimit this info to you. A crank is also balanced from the front to the rear. If it is not then it will start doing the worm from front to back.

Adding on stuff to the front will upset this balance. OFC the weights are tiny and there is quite a bit of tolerance, but as far as I know no one has run a CBC for the 50-100k km it might take for the symptoms to show up.


So in conclusion, why spend time and money on a solution that doesnt protect against the primary failure mode and that may even do more harm than good? And on something that happens to a fraction of a % of these engines. And lets forget price because you are min maxing to your advantage. Most SCH only result in off timing that does not result in 22k bill.

I understand one feels a need to justify their actions but one should also look at things objectively.

If this was such a great solution wouldn't BMW run this on their S55 engined race cars? Because loosing a race due to SCH is much much more expensive than this simple fix.

EDIT: Not to toot my own horn but I am a Mech Eng and my first job as an Eng was failure mode analysis of large diesel engines for a well known manufacturer. This entailed analysing why shit failed and proposing and designing fixes. A major issue we had was problems with bolted joints. Of which I was asked to carry out the calulations to ensure they were within spec or not.

[Got f1?]

Originally Posted by Megator

So in conclusion, why spend time and money on a solution that doesnt protect against the primary failure mode and that may even do more harm than good? And on something that happens to a fraction of a % of these engines. And lets forget price because you are min maxing to your advantage. Most SCH only result in off timing that does not result in 22k bill.

To me, this is an interesting point. I am certainly not as technically knowledgable as either you Megator or F87source.

I am thinking in this way and would love both your thoughts. Presuming that overall failure rate with SCH is low (low single digits as %?) and a subset with catastrophic failure at less than half (is that fair?), the exposure seems to be that if I have a SCH, it will more likely results in limp mode.

For clarity, engine is not currently modified at all, save for mid-pipe and rear section. If I do modify, I will not exceed stage 1 levels so under 500BHP. As I understand, these levels and lower are "safer" although not "safe".

Seems like risk is pretty low to me.

Thoughts?

[bmwfan1234]

Mine suffered the dreaded SCH after a few thousand miles on a "Mild" Stage 1 tune. Let's just say it was a MAJOR headache and after three weeks, i now have it back after fitting a full 1 piece hub upgrade and capture bolt.


скачать картинки пнг

[F87source]

Originally Posted by Megator

You are missunderstanding two fundamental issues

1) When you tighten a bolt it is the "free" part of the bolt which is elastically deformed (ie the distance between the bottom of the head which in this case rests on the hub and the end of the thread engament in this case where it threads into the crank) and therby the bolt exerts a preload on all the sandwiched components.

To put it another way you are stretching 9.8mm of "free" bolt length to 10mm (the thickness of the components being sandwiched). The bolt wants to be 9.8mm long, so it pulls everything together. It is esentially a stretched out spring clamping everything together. Just like a spring its force is proportional to the amount of stretch from its resting position.

When the hub spins then the length of the assembly also changes by a miniscule amount. So the bolt is no longer stretched to 10mm but 9.9mm. This results in a loss of preload without the bolt spinning or changing position with respect to the crank.

Easy backyard mechanic test. Take a bolt and nut and sandwich something between them you can remove once they are tight (like a U shaped washer). Now remove the between component and the nut and bolt are free to rotate with respect to each other again. Esentially this is what happens with SCH

CBC does nothing in this regard.

Once the preload is gone/reduced, the threads of the bolt no longer exert the same force on the threads of the crank and the bolt is free to back out.

But the damage was already done! You just get into a spiral where less preload = more SCH/ bolt backing out = even less preload = even more SCH/bolt backing out.

The way you explain it does not work. If the preload in the bolt was built solely between the bolt and crank then you could never ever in a 1000 years apply preload to the crank hub components.

The numbers are obv. made up and just to illustrate a point.

So to me your point 1 is the failure mode and point 2 is a symptom of the failure not a cause.


2) I am not talking about the rotational balance of the crank. I am talking about the balance from the front to the rear.

I dont know how better to transimit this info to you. A crank is also balanced from the front to the rear. If it is not then it will start doing the worm from front to back.

Adding on stuff to the front will upset this balance. OFC the weights are tiny and there is quite a bit of tolerance, but as far as I know no one has run a CBC for the 50-100k km it might take for the symptoms to show up.


So in conclusion, why spend time and money on a solution that doesnt protect against the primary failure mode and that may even do more harm than good? And on something that happens to a fraction of a % of these engines. And lets forget price because you are min maxing to your advantage. Most SCH only result in off timing that does not result in 22k bill.

I understand one feels a need to justify their actions but one should also look at things objectively.

If this was such a great solution wouldn't BMW run this on their S55 engined race cars? Because loosing a race due to SCH is much much more expensive than this simple fix.

EDIT: Not to toot my own horn but I am a Mech Eng and my first job as an Eng was failure mode analysis of large diesel engines for a well known manufacturer. This entailed analysing why shit failed and proposing and designing fixes. A major issue we had was problems with bolted joints. Of which I was asked to carry out the calulations to ensure they were within spec or not.

First off no hard feelings I am just trying to exchange ideas! we are all friends here on the forum trying to solve a crappy problem and I respect you opinion since you are an engineer and I am not. So really looking forward to hearing your response.


AH yes you are correct I see what you are say by the bolt stretches out.


However I am still unsure about 1 failure mode, especially when the entire industry keeps talking about mechanical vibrations shaking the bolt loose, which is why the CBC was made by a few companies (3 iirc). It also does not explain why the CBC solved the spun crank hub issue on multiple cars that had multiple crank hub failures on the stock bed plate, update bed plate etc. A few of these cars have had 10' of thousands of km placed on them.

This guy is one example, over 15 thousand miles in 2018 and now likely alot more, it is daily driven at 732 whp and launched alot:
https://f80.bimmerpost.com/forums/sh....php?t=1420455
https://f80.bimmerpost.com/forums/sh....php?t=1417704


That is why the industry believes the S55 has nasty harmonics that vibrates the bolt loose over time. Because if the hub spins you can see the friction marks on the hub, when the bolt goes loose you don't see those scoring marks. You also see the hub fail while driving at a steady rpm meaning it has to be vibration related, there is no jerking force caused by a sudden acceleration on the hub when it is moving at a constant speed. There are definitely harmonics involved I don't see any other answer for failures under these conditions.



Ah yes front and rear balance, I was wired on rotational balance. You do have a point here. I wonder how large the tolerances are since the crankshaft is attached to the flywheel and damper and there are alot of variations of the weights of these things without issue:

1) M2:
a) crank is 22.5 kg https://www.realoem.com/bmw/enUS/par...&q=11217602972
b) the damper shared by all F series is 3.445 kg https://www.realoem.com/bmw/enUS/par...&q=11237573655
c) The dual mass flywheel is 11.530 kg https://www.realoem.com/bmw/enUS/par...&q=21212283028

That is a difference of 8.085 kg rear to front. This decreases for single mass fly wheel users since the weight of the flywheel drops.


2) The m235i:
a) same crank shaft as the m2 at 22.500 kg https://www.realoem.com/bmw/enUS/par...&q=11217602972
b) dual mass fly wheel is 13.500 kg https://www.realoem.com/bmw/enUS/par...&q=21207638495
auto matic fly wheel is 1.924 kg https://www.realoem.com/bmw/enUS/par...&q=11228604045

so huge variation here
c) same harmonic damper at 3.445 kg https://www.realoem.com/bmw/enUS/par...&q=11237573655

so now you are seeing with a manual: 10.055 kg bias to the rear of the crank
with an auto: 1.521 kg bias to the front of the crank

Since the m2 and m235i share the exact same crank, the flywheel is the exact same throughout the F series n55 cars despite non forged crank shafts on the normal n55's this leads me to believe the n55 is internally balanced rotationally, not the point of our discussion here. The point is the huge variations in weight front to rear on the exact same crank shaft on various models of the n55. This leads me to believe (I can be totally wrong so ready to eat my words if proven) front to rear balance is not a huge factor. it could be because of the way the crank sits in the bed plate and is sandwiched down (could explain why the front bearings on the m2 have some increased wear vs. the rest of the bearings from a tear down I saw online as the rear of the crank would have more weight pushing the front up, they said it could also be due to the oil pump being driven off the front of the crank). This means a CBC will be fine since it is a very small weight added to the front of the crank.

[F87source]

Originally Posted by bmwfan1234

Mine suffered the dreaded SCH after a few thousand miles on a "Mild" Stage 1 tune. Let's just say it was a MAJOR headache and after three weeks, i now have it back after fitting a full 1 piece hub upgrade and capture bolt.


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Damn that sucks, glad you got it fixed.

Now 4 companies including mmr make the CBC.


BTW: how come your once piece hub does not look like it has pins on it? If it doesn't have a means to affix it to the crank the friction disk can still break loose, if that happens timing will still be thrown off if the hub moves.

[F87source]

Originally Posted by Got f1?

To me, this is an interesting point. I am certainly not as technically knowledgable as either you Megator or F87source.

I am thinking in this way and would love both your thoughts. Presuming that overall failure rate with SCH is low (low single digits as %?) and a subset with catastrophic failure at less than half (is that fair?), the exposure seems to be that if I have a SCH, it will more likely results in limp mode.

For clarity, engine is not currently modified at all, save for mid-pipe and rear section. If I do modify, I will not exceed stage 1 levels so under 500BHP. As I understand, these levels and lower are "safer" although not "safe".

Seems like risk is pretty low to me.

Thoughts?

Yeah it is only a small percentage that fails, no idea why, and yes an even smaller percentage have catastrophic engine failure. Yup if you spin you most likely will get a limp mode because the ecu and crank position sensor is so damn good. Good job bmw!


There is no defining power that makes it safe or not safe. It can spin stock too, albeit more power seems to make it more likely to spin. But the issue seems to be rpm related as well, so if you have a huge jump in rpm you could spin it.


IMO I always would go for a solution because I don't want to be a statistic. Also because I am paranoid af.

[Megator]

Originally Posted by Got f1?

To me, this is an interesting point. I am certainly not as technically knowledgable as either you Megator or F87source.

I am thinking in this way and would love both your thoughts. Presuming that overall failure rate with SCH is low (low single digits as %?) and a subset with catastrophic failure at less than half (is that fair?), the exposure seems to be that if I have a SCH, it will more likely results in limp mode.

For clarity, engine is not currently modified at all, save for mid-pipe and rear section. If I do modify, I will not exceed stage 1 levels so under 500BHP. As I understand, these levels and lower are "safer" although not "safe".

Seems like risk is pretty low to me.

Thoughts?

First of all this is all speculation, I only have internet stories to go by, my experience, and parts diagrams to make an educated guess.


In my mind its not so much about power but torque and changes in RPM/power output. When you jump from cruising at 2-3rpm to 6.5-7krpm full bore (using kickdown for example). The rotating assemblies attached to the various crank hub components need to be spun up by 5k rpm in an instant. This requires a huge amount of torque/force.

So on the one hand you have the crank being accelerated in one direction to reach 7k rpm and output power, and on the other hand you have a rotating assembly that is "braking" the crank. Everything still spins clockwise, the rotating assembly is just saping TQ out.

All that force is only held back by the preload and friction between the various components of the crank hub.

Increasing engine TQ causes that delta to be even greater, leading to more chances of a SCH.

So do you need a CBC? well that depends on so many factors. Are you keeping the car for longer than the warranty? How risk averse are you? Do you plan to run a bunch of TQ? do you regularly launch and or use kickdown? Are you OK investing several 100$ on something that might be snake oil?

As for statistical analysis, this is impossible to do 100% accurately even for BMW. It is very hard as an engineer to get accurate data back from the field. Sometimes all we get is an excel sheet with vague cusotmer comments! At most BMW will know how many SCH have been warrantied. They will be blind to post warranty/tuned cars and maybe even cases where warranty work was rejected.

So at this point my gut feeling says it affect 1% or less of these engines. With maybe 10% of that being catastrophic failure.

F87source good sleuthing I think you are right that the CBC does not affect balance much. It was just something to consider. However you quoted N55 and not S55 parts.

That multiple tuners offer a solution does not mean its a good one. I had Focus RS, they shat their engines for a while, everyone had fixes. Guess what none were 100% right and even Ford's solution is a bit of a bandaid.

The failure modes are hard to ascertain without some further testing. It is all combined though and hard to say which occurs 1st or if they occur in combination.

"That is why the industry believes the S55 has nasty harmonics that vibrates the bolt loose over time. Because if the hub spins you can see the friction marks on the hub, when the bolt goes loose you don't see those scoring marks. You also see the hub fail while driving at a steady rpm meaning it has to be vibration related, there is no jerking force caused by a sudden acceleration on the hub when it is moving at a constant speed. There are definitely harmonics involved I don't see any other answer for failures under these conditions."

Do you have a source for this? I would like to see the witness marks myself. It can be so many factors, if the joint was already slightly weakend thermal expansion could push it over the edge.


So if you look at the hub and BMWfans pics highlight this, the CBC does nothing to further mechanically connect the crank hub to the crank. All it does is rotationally fix the bolt to the front vibration damper/belt drive pulley.

It in no mechanical geomteric way stops the bolt from backing out of the crank.

I postulate that IF the CBC does indeed work, then it is not by "holding" the bolt but by moving some harmonics on the crankshaft/bolt.

As to people having repeated failure that are solved by the CBC, this is an anecdote and not hard data point. So many variables that were likely not controlled make this hard to take as fact or data.


Hell my RS suffered from SCH even though that is unheard of on the RS engine (similar crank/hub connection). It did so because the mechanics put in an old used friction washer (per Ford's instructions) and likely didnt get everything as clean as needed. I was a major outlier here just like the other guys might be.

[F87source]

Originally Posted by Megator

First of all this is all speculation, I only have internet stories to go by, my experience, and parts diagrams to make an educated guess.

Yeah me too, only info I have to go off of is reading paranoia inducing threads one after the other and talking to vendors, engineers, and mechanics in this industry. The only two conclusions I keep hearing reverberated is vibrations backing the bolt out and the friction disc slipping.

Originally Posted by Megator

In my mind its not so much about power but torque and changes in RPM/power output. When you jump from cruising at 2-3rpm to 6.5-7krpm full bore (using kickdown for example). The rotating assemblies attached to the various crank hub components need to be spun up by 5k rpm in an instant. This requires a huge amount of torque/force.

So on the one hand you have the crank being accelerated in one direction to reach 7k rpm and output power, and on the other hand you have a rotating assembly that is "braking" the crank. Everything still spins clockwise, the rotating assembly is just saping TQ out.

All that force is only held back by the preload and friction between the various components of the crank hub.

Increasing engine TQ causes that delta to be even greater, leading to more chances of a SCH.

No disagreements from me, it's pretty much what I said earlier about having to accelerate the inertia putting alot of counter clockwise torque on the hub spinning it.

Originally Posted by Megator

So do you need a CBC? well that depends on so many factors. Are you keeping the car for longer than the warranty? How risk averse are you? Do you plan to run a bunch of TQ? do you regularly launch and or use kickdown? Are you OK investing several 100$ on something that might be snake oil?

No disagreements here. But $100 is alot cheaper than the other bmw taxed products, if you get it on sale too then it's even cheaper if you just want something to play with.

Originally Posted by Megator

As for statistical analysis, this is impossible to do 100% accurately even for BMW. It is very hard as an engineer to get accurate data back from the field. Sometimes all we get is an excel sheet with vague cusotmer comments! At most BMW will know how many SCH have been warrantied. They will be blind to post warranty/tuned cars and maybe even cases where warranty work was rejected.

So at this point my gut feeling says it affect 1% or less of these engines. With maybe 10% of that being catastrophic failure.

You are absolutely right, unless you are one of those lucky good will people you are going to be out of luck with bmw. Also agreed on the likely failure rate being 1%, but keep in mind there are ALOT of M owners who drive their cars like regular cars, comfort mode don't even accelerate etc. They pretty much bought it for the prestiege.

Originally Posted by Megator

F87source good sleuthing I think you are right that the CBC does not affect balance much. It was just something to consider. However you quoted N55 and not S55 parts.

Thanks! You had me on a loop not gonna lie, I was so worried about this issue messing up the crank I had to do some digging into it. Yup quoted N55 because of 2 reasons:
1) I have an N55 m2
2) There is no way to compare the S55 engine to anything because there are no close equivalents, too many factors would be off.

Originally Posted by Megator

That multiple tuners offer a solution does not mean its a good one. I had Focus RS, they shat their engines for a while, everyone had fixes. Guess what none were 100% right and even Ford's solution is a bit of a bandaid.

The failure modes are hard to ascertain without some further testing. It is all combined though and hard to say which occurs 1st or if they occur in combination.

Exactly correct, iirc TPG tuning made the first "fix" and that was a horrendous attempt and iirc it blew engines and caused them to leave the forum from the back lash. i'm just glad we have people trying to fix it and not abandoning us.

Originally Posted by Megator

"That is why the industry believes the S55 has nasty harmonics that vibrates the bolt loose over time. Because if the hub spins you can see the friction marks on the hub, when the bolt goes loose you don't see those scoring marks. You also see the hub fail while driving at a steady rpm meaning it has to be vibration related, there is no jerking force caused by a sudden acceleration on the hub when it is moving at a constant speed. There are definitely harmonics involved I don't see any other answer for failures under these conditions."

Do you have a source for this? I would like to see the witness marks myself. It can be so many factors, if the joint was already slightly weakend thermal expansion could push it over the edge.

It's in a thread somewhere can't remember if it was this forum, SS, BB, BF, or a british forum.

Originally Posted by Megator

So if you look at the hub and BMWfans pics highlight this, the CBC does nothing to further mechanically connect the crank hub to the crank. All it does is rotationally fix the bolt to the front vibration damper/belt drive pulley.

It in no mechanical geomteric way stops the bolt from backing out of the crank.

No it does not add any other attachment of the hub to the crank shaft, it only functions to prevent the bolt from backing out which is why it is called the crank bolt capture.

Yes it does prevent the bolt from backing out, since it locks the bolt to the hub it cannot rotate counter clockwise to loosen due to vibrations.

Originally Posted by Megator

I postulate that IF the CBC does indeed work, then it is not by "holding" the bolt but by moving some harmonics on the crankshaft/bolt.

It could be a factor albeit I don't think it is the case since all of the vibrations should be delt with by the deformation of the elastomeric ring. If it really is harmonics then maybe if ATI made a super damper for the N55/S55, it solved alot of vibration issues on the S54 and they even have one for the N54.

Originally Posted by Megator

As to people having repeated failure that are solved by the CBC, this is an anecdote and not hard data point. So many variables that were likely not controlled make this hard to take as fact or data.

True, but good to see something imo.

Originally Posted by Megator

Hell my RS suffered from SCH even though that is unheard of on the RS engine (similar crank/hub connection). It did so because the mechanics put in an old used friction washer (per Ford's instructions) and likely didnt get everything as clean as needed. I was a major outlier here just like the other guys might be.

That sucks man, and I was close to buying an RS too... So glad I didn't.

Dude don't even get me started LOL, I might go on a blind rant. Let me just be brief:
1) I hate dealerships and their techs. I never can trust them, it always worries me bringing the car there.

2) every time I hear engine failures I get huge PTSD flash backs from my subaru ej257 days. The number of times I had that engine blow stock and rebuilt with forged internals and done properly by reputable builders, and the number of times I had to rebuild that engine gives me nightmares. (Damn ringland failure, spun bearings, blow turbos, head gaskets, cylinder number 4 over heating all the damn time, rod knock, piston slap)

[Megator]

Originally Posted by F87source

No it does not add any other attachment of the hub to the crank shaft, it only functions to prevent the bolt from backing out which is why it is called the crank bolt capture.

Yes it does prevent the bolt from backing out, since it locks the bolt to the hub it cannot rotate counter clockwise to loosen due to vibrations.

The vibration comment was pure speculation from someone, it was in one of your posted threads. The S55 is a straight 6 which is very good for vibrations. I was under my mates M4 after installing DP and the engine hardly moves as you ramp up the RPMs.

Ok not to be rude but how does it capture the bolt with respect to the crankshaft if there is no additional connection?????

All the CBC does is connect the bolt to another component that is free to rotate with respect to the crank. Its like locking a nut on a bolt to a washer compressed by said nut and bolt...

Put it another way, if the head of the bolt was long enough I could back the bolt out of the crank with a wrench whether the CBC is installed or not.

The only improvement that the CBC is capable of is increasing the friction with with which the head of the bolt rests on the hub. Ie the forces holding the bolt tight are the friction between the threads and friction under the head of the bolt. CBC increases the under head bolt friction. But its of little use as that frictional force is limited to the frictional forces between the hub and the timing gear. It can never be higher than that force as that is the force holding the hub in place.

Come to think of it this is a good test for the CBC, back the bolt out with and witout CBC and compare the TQs required to do so. If CBC works then the release TQ of CBC should be considerably higher.

[F87source]

Originally Posted by Megator

The vibration comment was pure speculation from someone, it was in one of your posted threads. The S55 is a straight 6 which is very good for vibrations. I was under my mates M4 after installing DP and the engine hardly moves as you ramp up the RPMs.

Ok not to be rude but how does it capture the bolt with respect to the crankshaft if there is no additional connection?????

All the CBC does is connect the bolt to another component that is free to rotate with respect to the crank. Its like locking a nut on a bolt to a washer compressed by said nut and bolt...

Put it another way, if the head of the bolt was long enough I could back the bolt out of the crank with a wrench whether the CBC is installed or not.

The only improvement that the CBC is capable of is increasing the friction with with which the head of the bolt rests on the hub. Ie the forces holding the bolt tight are the friction between the threads and friction under the head of the bolt. CBC increases the under head bolt friction. But its of little use as that frictional force is limited to the frictional forces between the hub and the timing gear. It can never be higher than that force as that is the force holding the hub in place.

Come to think of it this is a good test for the CBC, back the bolt out with and witout CBC and compare the TQs required to do so. If CBC works then the release TQ of CBC should be considerably higher.

That's the issue it's a hypothesis that the bolt vibrates out, I believe it was based at looking at the failed hubs and scarring marks and people concluded that. If you want more details you should probably ask the makers of the hub, because it will take me forever to read through and find these threads again. So the best way to get info is talking to these companies, I can do my best to relay the things I have learned over the years but that can come with inaccuracies if I remember things wrong.

Maybe at higher rpms it introduces more vibrations than at idle.


You are absolutely correct. That's another issue it doesn't lock it to the crank. It locks the bolt to the hub so it can't vibrate loose unless the hub slips, and since it is more common for the friction disk to fail the bolt should never back out. So essentially you are coupling the two failure points together. That is why the CBC is always marketed as a partial solution and it will not fully protect your engine unless you have a crank hub fix first.



I would like to see more tests too but I doubt any manufacture will do it. But I don't see how your test would work, with the CBC on to back the bolt out you have to spin the whole hub since they are connected as a single unit with the CBC on.

[Megator]

Originally Posted by F87source

That's the issue it's a hypothesis that the bolt vibrates out, I believe it was based at looking at the failed hubs and scarring marks and people concluded that. If you want more details you should probably ask the makers of the hub, because it will take me forever to read through and find these threads again. So the best way to get info is talking to these companies, I can do my best to relay the things I have learned over the years but that can come with inaccuracies if I remember things wrong.

Maybe at higher rpms it introduces more vibrations than at idle.


You are absolutely correct. That's another issue it doesn't lock it to the crank. It locks the bolt to the hub so it can't vibrate loose unless the hub slips, and since it is more common for the friction disk to fail the bolt should never back out. So essentially you are coupling the two failure points together. That is why the CBC is always marketed as a partial solution and it will not fully protect your engine unless you have a crank hub fix first.



I would like to see more tests too but I doubt any manufacture will do it. But I don't see how your test would work, with the CBC on to back the bolt out you have to spin the whole hub since they are connected as a single unit with the CBC on.

A bolt under tension does not just vibrate loose. If loosening under vibration was an issue then there are like 5 cheap and fast fixes BMW could have implemented which would all cost much less than the warranties on S55 engines.

The bolt is like a spring right, for it to vibrate loose the pretension on it must be reduced to the point where the mechanical loads on it can cause it to slip. This can happen for example in very hot conditions where a bolt expands more than the bits its holding together.

Or from vibration forces which might "pry" the joint open allowing the bolt to somewhat back off. I dont really see how this plays a role on the S55 unless the crank is literaly slaming back and forwards in the engine like an old diesel.

Just found this great explanation of the crank hub and CBC from TPS performance, its in German but allows auto generated translated captions.

I am not sure about what all CBC sellers recommend but TPS fits new OEM friction rings and bolt and increase the tightening TQ (by increasing the final angle added by 90 degrees) and add Loctite!

2 of those 3 things are proven fixes for bolts that "vibrate" loose

Also here is a pic of a failed CBC. As you can see the CBC bolts have been sheared off in the hub. That can only occur if the CBC spins with respect to the hub...

In that youtube vid another user complains of the same issue and another of SCH symptoms after installing the CBC.

"Enrico Rieck 1 month ago
Ich habe eine kurbelwellenverstärkung einbauen lassen bei einer werkstatt plus leistungssteigerung auf 560 PS und nach einem dreiviertel Jahr ca habe ich jetz den mist!! Versicherung zahlt nicht und ich bleib auf den Schaden sitzen!! Ich habe die kurbelwellenverstärkung selbst gekauft und der Werkstatt zum einbauen dazu gelegt.
Bei mir waren aber kurze alu schrauben dabei die sich jetzt durch das Material gedrückt haben und Drehmoment mit dem die befestigt wurden weiß ich nicht!! Meine Frage sollte die Werkstatt wissen das man solche Schrauben nicht benutzt??"

As to my test the point is to measure which one is harder to back out bolt or CBC + bolt. If it is harder to back out with CBC then it means its doing something for vibration/losening. If its about the same then the CBC is not doing anything for vibration/losening.

Anyways reading the youtube comments to that TPS vid brings out another potential problem of the CBC that I had not thought about. When the crank spins up it also spins up the bolt.

Now normally a bolt weighs too little for its moment of inertia to play a roll in the bolt backing out.

But with the CBC you attach the mass of the hub and pulley etc to the bolt increasing its moment of inertia. Thereby increasing the chances of the bolt backing out due to the loosening force exerted on it.

Its true that the hub is always rotationally held in place by the bolt. What changes is that the hub is now mechanically and frictionally rotationally held in place. The new mechanical connection transmitts the force directly to the threads of the bolt instead of the preload of the joint.

That can lead to a violent loosening of the crankhub, resulting in the sheared bolts of the failed CBC.

If anyting, increase the TQ on the hub bolt and fix it with loctite or something. That leaves out the inertia issue, solves a "vibration" issue, and increases the clamping force on all the components of the crank hub.