[F87source]

Originally Posted by SpecialEdition_F87

The crank bolt isn’t going anywhere near ever rounding with a CBC I’ll tell you that right now lol.

It is extremely unlikely unless it gets really corroded, but what is more likely is the soft aluminium CBC gets damaged.

[F87source]

Originally Posted by SpecialEdition_F87

Post the link. Let’s see it. What was the power level? What mileage did he get the job done at?

CBC should be done at relatively low miles on 91.

If you get the job done “ after warranty “ or before hell the longer you wait the worse off you are. 200nm is what the bolts at if you install the CBC when the bolt is at 160nm backed out your just holding the bolt from going further. Less force on friction disks.

Send the link let’s see this post

But what you don't understand is that even if the CBC stops the crank bolt from coming loose (meaning the same amount of clamping pressure is maintained on those friction disks) the friction disks themselves are not fixed and if the impluse from the drive line is high enough during a downshift it will still spin. There is nothing the CBC can do to prevent the friction disks from slipping.


I'm all for the CBC and have said in the past it can help alleviate issues of the bolt coming loose, but it is not a full solution regardless of power levels - at best it is a bandaide. You may not see any issues on the forums, but there are more users out there that could have had an issue and not reported it because they are not on the forums.

[M2_MEDUSA]

Originally Posted by F87source

But what you don't understand is that even if the CBC stops the crank bolt from coming loose (meaning the same amount of clamping pressure is maintained on those friction disks) the friction disks themselves are not fixed and if the impluse from the drive line is high enough during a downshift it will still spin. There is nothing the CBC can do to prevent the friction disks from slipping.


I'm all for the CBC and have said in the past it can help alleviate issues of the bolt coming loose, but it is not a full solution regardless of power levels - at best it is a bandaide. You may not see any issues on the forums, but there are more users out there that could have had an issue and not reported it because they are not on the forums.

Once again let me repeat myself and say these friction disks will not fail if the CBC is installed at the proper low mileage and keeping it tuned on pump only. ZERO reported failures under 600whp that wasn’t money shifted. For me I’m CBC all the way. All you need.

[F87source]

Originally Posted by SpecialEdition_F87

Once again let me repeat myself and say these friction disks will not fail if the CBC is installed at the proper low mileage and keeping it tuned on pump only. ZERO reported failures under 600whp that wasn’t money shifted. For me I’m CBC all the way. All you need.

But the problem is you don't have any solid data...

First of all an S55 that is stock/sub 600whp already has an extremely low chance of getting a spun crank hub. These events are extremely rare.

The next thing that is extremely rare are cars with a crank bolt capture installed.


Take those two probabilities and multiply then together to get the probability that you have a stock/sub 600whp S55 powered car that has a CBC and experiences a spun crank hub is extremely extremely rare, so that could be why we don't see any failures....

[doughboy]

Originally Posted by F87source

But the problem is you don't have any solid data...

First of all an S55 that is stock/sub 600whp already has an extremely low chance of getting a spun crank hub. These events are extremely rare.

The next thing that is extremely rare are cars with a crank bolt capture installed.


Take those two probabilities and multiply then together to get the probability that you have a stock/sub 600whp S55 powered car that has a CBC and experiences a spun crank hub is extremely extremely rare, so that could be why we don't see any failures....

The joy of statistics and probability - and the human perception of risk that often misjudges both of those by a mile...

[F87source]

Originally Posted by doughboy

The joy of statistics and probability - and the human perception of risk that often misjudges both of those by a mile...

That's why I'm giving emperical numbers. It's also impossible to say zero with certainty when examining the population set of just the forums...

[doughboy]

Originally Posted by F87source

I can't remember what you said about this issue before so could you tag me in that post or summarize it?..

I can't remember either! but similarly it was around the crank rotation direction and that it was rate of change of increase of RPM related rather than just power output on it's own.

As output torque increases then crankshaft vibrations will increase over the normal ones that the hub and heavy pulley are designed to cancel out (it isn't called a vibration damper for nothing).

In my understanding a fixed damper like this reduces vibrations by adding intertia / mass in opposition to the crank oscillations (tiny tiny amounts), either rotational or longitudinal in direction. All of these balancing forces acting directly on the friction discs and clamp assembly.

Maybe the tuned hi output / high vibration operation mode may compromise / compress the friction / clamping then allowing hub slip when a suitably violent rpm increase occurs in the future?

But the thing is even if an 800 horse power m3 doesn't down shift quicker it will definitely be able to rev faster and more agressively than a stock m3 and in any gear once boost kicks in. This will also be a factor in spinning the hub. So now you also have the factor of every acceleration causing more stress along with every down shift.

Surely though no matter how much power you have, the in-gear engine RPM will never jump as quick as it does on an neutral blip or aggressive DCTdownshift?

I'm just glad I drive a 6MT, and do so with mechanical sympathy, and I've mapped out the rev match permanently with BM3. So in all honesty I don't lose any sleep over hub slip, CBC or not.

[F87source]

Originally Posted by doughboy

I can't remember either! but similarly it was around the crank rotation direction and that it was rate of change of increase of RPM related rather than just power output on it's own.

As output torque increases then crankshaft vibrations will increase over the normal ones that the hub and heavy pulley are designed to cancel out (it isn't called a vibration damper for nothing).

In my understanding a fixed damper like this reduces vibrations by adding intertia / mass in opposition to the crank oscillations (tiny tiny amounts), either rotational or longitudinal in direction. All of these balancing forces acting directly on the friction discs and clamp assembly.

Maybe the tuned hi output / high vibration operation mode may compromise / compress the friction / clamping then allowing hub slip when a suitably violent rpm increase occurs in the future?




Surely though no matter how much power you have, the in-gear engine RPM will never jump as quick as it does on an neutral blip or aggressive DCTdownshift?

I'm just glad I drive a 6MT, and do so with mechanical sympathy, and I've mapped out the rev match permanently with BM3. So in all honesty I don't lose any sleep over hub slip, CBC or not.

Well for the most part inline 6 engines are perfectly balanced as is, with all harmonics mostly being canceled out. Those minor harmonics left over are corrected for by the dampener.

I don't see these harmonics being able to directly loosen the crank bolt, and I don't see the "worming" motion being enough for the bolt to really hit anything that would cause it to loosen. So I really can't see how the bolt comes loose on its own without the hub spinning TBH. Otherwise pinned hubs would have failed regardless, because as soon as that crank bolt is loose there would be less friction and clamping force thus putting alot of stress directly on the pins by itself, which was designed to work in conjunction with the friction disk to handle to load and not alone (just like a woodruff key design would work). This likely would cause the pinned hubs to fail over time as the pins snap, and since we don't see that I really don't know if the bolt comes loose by itself, especially since it's a tty bolt and once that thread is stretched (180°- 360° iirc) it's really stuck in there against vibrations.


Now in terms of the friction disk you might be right, a huge amount of harmonics causing it to move right when there's a huge load could cause it to slip.


Maybe in 1st with alot of power rpms could jump quickly, but now that rpm increase occurs quickly every where in the power band all the time. So eventually it can cause a failure. But no, nothing beats rpm increase like a huge dct kick down of multiple gears or revving in neutral. But there's not much cylinder pressure revving in neutral vs. high boost so all that extra boost pushing on the valves does add more load to the timing chain. Could be another reason high power cars fail, but how much extra load idk. But revving in neutral with no load is no where near as bad as a dct kick down. Hence why you see a disproportionate amount of dct failures vs 6mt. Rev match should stay on, otherwise you could have drive train shock introduced on down shifts which would be worse.

So imo down shifting with rev match is fine, and revving in neutral is fine (as long as you're not bouncing off the rev limiter), the thing you should be worried about is multiple gears down shifts in one go or dct kick downs.

[Megator]

Originally Posted by SpecialEdition_F87

Post the link. Let’s see it. What was the power level? What mileage did he get the job done at?

CBC should be done at relatively low miles on 91.

If you get the job done “ after warranty “ or before hell the longer you wait the worse off you are. 200nm is what the bolts at if you install the CBC when the bolt is at 160nm backed out your just holding the bolt from going further. Less force on friction disks.

Send the link let’s see this post

Mate your posts are super confusing and full of pure speculation. If you don't have anything useful to say that is backed by good engineering principels or hard data then please keep to yourself.

The torque applied to a bolt is not equivalent to the preload on a bolt. There are many many sources of error meaning that 10 bolts torqued in exactly the same way can have up to 25% varriation in preload. I know as I am an engineer and did many bolted joint analysis when I worked for Cummins Diesel Engines.

This is why you use TTY bolts, they ensure the bolted joint preload becomes more consistent as you are relying on plastic deformation and not elastic deformation. This means you are more certain of where on the yield curve the material is and therefore the preload it exerts.

Originally Posted by F87source

I think it was a clockwise spin not counter clockwise as judged by the shear marks on the cbc. So I think it was just a sudden spin of the crank hub which caused this. In this case it wouldn't have loosened the crank bolt but since the whole hub spun likely damage was inevitable, compared to just the friction disk spinning a bit.

Let me clarify by CBC I mean only a crank bolt capture plate. A one piece or pinned or splined hub in theory should solve the problem (if it does not introduce others).

When the crank hub fails it happens "quickly" the engine is spinning at 1000RPM at idle thats already 16 un/load cycles a second... The difference im talking about is did it happen in 5 revs or a couple 1000 revs not hours worth of revs.

I am not sure I follow your witness mark analysis. The CBC as shown in the left pic usually spins clockwise. The witness marks are extended counter clockwise, this is obvious as they are A) clean and B) dont have the witness marks of the grooves on the underside of the bolts since the leading edge of the bolt smooshed the aluminium nice and smoothly.

The whole point of my post was that the CBC DOES NOT prevent the "sudden spin" as you label it, and IN FACT exacerbates the whole ordeal by backing out the crank bolt out of the crank once the "sudden spin" has occured.

Lets make things clear I am not talking about it fully unwinding the crank bolt but undoing it 5,10,15 degrees. This further reduces preload by an amount significant enough to cause timing gears to further slip and boom pistons meet valves.

Without the CBC this "2nd" slip is less likely to occur, hence why we see many SCH that only need a retime.

Making the CBC out of Ti or gods own tears won't help as the CBC does nothing for the root cause of the failure which is that the timing gear, oil pump gear, accesory pulley, and crank are only held together in rotation by friction.

This friction in some situations ends up being insufficient for the torque applied to the rotating components.

The CBC does nothing to increase this friction. It doesn't even help maintain this friction, because as previously explained the CBC only stops the crank bolt from rotating via the same damn friction rings holding everything together already.


It seems ever more likely that the variation in friction disc friction is to blame or the surface finish of the components clamping it. Under the right conditions these do not provide sufficient friction force to hold the timing gear in place. This can happen without a significant loss in preload or the bolt backing out as evidenced by the attached post and the fact that many SCH cars can still be driven in limp mode after SCH. If the bolt backed out at all, you would expect the failure to rapidly cascade meaning pistons meet valves.

[F87source]

Originally Posted by Megator

Mate your posts are super confusing and full of pure speculation. If you don't have anything useful to say that is backed by good engineering principels or hard data then please keep to yourself.

The torque applied to a bolt is not equivalent to the preload on a bolt. There are many many sources of error meaning that 10 bolts torqued in exactly the same way can have up to 25% varriation in preload. I know as I am an engineer and did many bolted joint analysis when I worked for Cummins Diesel Engines.

This is why you use TTY bolts, they ensure the bolted joint preload becomes more consistent as you are relying on plastic deformation and not elastic deformation. This means you are more certain of where on the yield curve the material is and therefore the preload it exerts.



Let me clarify by CBC I mean only a crank bolt capture plate. A one piece or pinned or splined hub in theory should solve the problem (if it does not introduce others).

When the crank hub fails it happens "quickly" the engine is spinning at 1000RPM at idle thats already 16 un/load cycles a second... The difference im talking about is did it happen in 5 revs or a couple 1000 revs not hours worth of revs.

I am not sure I follow your witness mark analysis. The CBC as shown in the left pic usually spins clockwise. The witness marks are extended counter clockwise, this is obvious as they are A) clean and B) dont have the witness marks of the grooves on the underside of the bolts since the leading edge of the bolt smooshed the aluminium nice and smoothly.

The whole point of my post was that the CBC DOES NOT prevent the "sudden spin" as you label it, and IN FACT exacerbates the whole ordeal by backing out the crank bolt out of the crank once the "sudden spin" has occured.

Lets make things clear I am not talking about it fully unwinding the crank bolt but undoing it 5,10,15 degrees. This further reduces preload by an amount significant enough to cause timing gears to further slip and boom pistons meet valves.

Without the CBC this "2nd" slip is less likely to occur, hence why we see many SCH that only need a retime.

Making the CBC out of Ti or gods own tears won't help as the CBC does nothing for the root cause of the failure which is that the timing gear, oil pump gear, accesory pulley, and crank are only held together in rotation by friction.

This friction in some situations ends up being insufficient for the torque applied to the rotating components.

The CBC does nothing to increase this friction. It doesn't even help maintain this friction, because as previously explained the CBC only stops the crank bolt from rotating via the same damn friction rings holding everything together already.


It seems ever more likely that the variation in friction disc friction is to blame or the surface finish of the components clamping it. Under the right conditions these do not provide sufficient friction force to hold the timing gear in place. This can happen without a significant loss in preload or the bolt backing out as evidenced by the attached post and the fact that many SCH cars can still be driven in limp mode after SCH. If the bolt backed out at all, you would expect the failure to rapidly cascade meaning pistons meet valves.

No I meant put a witness mark on the crank bolt to see if it does vibrate loose. They sell torque seal which forms a little line that breaks if the bolt moves. This way you don't have to follow bad advice and keep torquing the crank bolt in efforts of preventative maintenance...


In terms of the cbc I just thought the break lines looked like a clockwise spin, because when you think about the rotation only the crank hub can change speeds compared to the crank bolt when it spins as the hub gets the torque from the timing chain etc. So in this case it looks like the hub spun clockwise and the crank bolt didn't move causing it to cut those lines. The second cause could be the bolt coming loose aka going counter clockwise and the bolt capture doing nothing to stop it, hence why if it were titanium maybe it would have a better chance of stopping the bolt of spinning loose (if it did spin loose). But again I'm on the same page as you the only thing a cbc can do is stop the bolt coming loose not preventing the friction disks from slipping which is another source of failure - I have been saying this since the beginning too.

[F87source]

I don't what else to say, I guess I'll just offer my last $0.02 before I leave this thread as I don't feel like I have anything else to offer.

1) if you're under warranty don't do anything otherwise you'll likely be denied coverage.


Post warranty:

2) there's still no solid evidence of the crank bolt coming loose, but if you want add a cbc as it should help prevent the crank bolt from coming loose if it does indeed come loose via a still unknown mechanism. However don't expect this to be a bullet proof solution because it's not as the friction disks can still slip, and if you are unlucky in the direction the hub spins it can loosen the crank bolt as well - which would make it worse.


3) a full solution would be a splines or pinned hub.

[AmooManiak]

Guys, I'm really curious what type of failure rates we are seeing on the M2Cs as I am looking to tune my car and would like to know how increased power correlates to failure rates. I created a poll below.

https://f87.bimmerpost.com/forums/sh....php?t=1812840

[F87source]

Originally Posted by AmooManiak

Guys, I'm really curious what type of failure rates we are seeing on the M2Cs as I am looking to tune my car and would like to know how increased power correlates to failure rates. I created a poll below.

https://f87.bimmerpost.com/forums/sh....php?t=1812840

There was a really indepth thread on f80post with polls iirc.

[M2_MEDUSA]

Lol it's funny to me how companies that sell products say they've only heard and to buy their more expensive product with no actual proof. People constantly say CBC doesn't work and shouldn't be trusted and use some human psychology and knowledge to explain why.

Yet no matter how many times people ask for proof it's the same old money shifted or high power cars.

Say what you want about what y'all's beliefs are I go off what's been seen in the field. I don't listen to people who claim to know a guy who knows a guys guys friends brothers uncle.

CBC is the only product that has experienced no SCH outside of higher power and not money shifted and the fact that it's $100 and 2 hours of labor makes it better

And here we are almost 2 years later with STILL no proof yet proof of SCH on pinned crank hubs and other hubs just saying

[Megator]

Originally Posted by SpecialEdition_F87

Lol it's funny to me how companies that sell products say they've only heard and to buy their more expensive product with no actual proof. People constantly say CBC doesn't work and shouldn't be trusted and use some human psychology and knowledge to explain why.

Yet no matter how many times people ask for proof it's the same old money shifted or high power cars.

Say what you want about what y'all's beliefs are I go off what's been seen in the field. I don't listen to people who claim to know a guy who knows a guys guys friends brothers uncle.

CBC is the only product that has experienced no SCH outside of higher power and not money shifted and the fact that it's $100 and 2 hours of labor makes it better

And here we are almost 2 years later with STILL no proof yet proof of SCH on pinned crank hubs and other hubs just saying

You are commiting several logical fallacies in your reasoning

1) That you have perfect knowldege of all SCH cars. You cannot with any certainty say that CBC equiped cars don't experience SCH. You presumably don't go to every single S55 forum/fb group/etc, and keep a detailed excel sheet of what happened to each CBC equipped car.

Also not all CBC equiped car owners are on forums, and not everyone with a CBC feels the need to tell the world theirs failed.

The data to say CBC always works is simply not there.

Ergo you cannot with any certanty say "CBC is the only product that has experienced no SCH outside of higher power and not money shifted"

Also what is "high power"? pretty sure the failed CBC I showed was only a stage 1 or 2 car and it wasn't a money shift.

2) That CBC equiped cars were "destined" to fail and that CBC prevented this. We cannot know if the CH was always going to be fine and the CBC did nothing or if the CBC was the only thing keeping everything together.

Ergo you cannot with any certainty say that CBC "fixes" SCH.

One could only say this once they can replicate SCH on command, add a CBC, and then have SCH stop happening. As no one seems to know the root cause of SCH, no one can reliably replicate the failure, and no one can reliably prove their fix works.

Originally Posted by F87source

I don't what else to say, I guess I'll just offer my last $0.02 before I leave this thread as I don't feel like I have anything else to offer.

1) if you're under warranty don't do anything otherwise you'll likely be denied coverage.


Post warranty:

2) there's still no solid evidence of the crank bolt coming loose, but if you want add a cbc as it should help prevent the crank bolt from coming loose if it does indeed come loose via a still unknown mechanism. However don't expect this to be a bullet proof solution because it's not as the friction disks can still slip, and if you are unlucky in the direction the hub spins it can loosen the crank bolt as well - which would make it worse.


3) a full solution would be a splines or pinned hub.

I agree with 1 and 3. Not so sure on 2. See my diagram below.

The CBC is like tying your boat to the dock via a line that is already tied to the dock. In this situation the 2nd line will do nothing to hold the boat to the dock if the 1st line is cut.

[NathObeaN]

Originally Posted by Megator

You are commiting several logical fallacies in your reasoning

1) That you have perfect knowldege of all SCH cars. You cannot with any certainty say that CBC equiped cars don't experience SCH. You presumably don't go to every single S55 forum/fb group/etc, and keep a detailed excel sheet of what happened to each CBC equipped car.

Also not all CBC equiped car owners are on forums, and not everyone with a CBC feels the need to tell the world theirs failed.

The data to say CBC always works is simply not there.

Ergo you cannot with any certanty say "CBC is the only product that has experienced no SCH outside of higher power and not money shifted"

Also what is "high power"? pretty sure the failed CBC I showed was only a stage 1 or 2 car and it wasn't a money shift.

2) That CBC equiped cars were "destined" to fail and that CBC prevented this. We cannot know if the CH was always going to be fine and the CBC did nothing or if the CBC was the only thing keeping everything together.

Ergo you cannot with any certainty say that CBC "fixes" SCH.

One could only say this once they can replicate SCH on command, add a CBC, and then have SCH stop happening. As no one seems to know the root cause of SCH, no one can reliably replicate the failure, and no one can reliably prove their fix works.

I agree with 1 and 3. Not so sure on 2. See my diagram below.

The CBC is like tying your boat to the dock via a line that is already tied to the dock. In this situation the 2nd line will do nothing to hold the boat to the dock if the 1st line is cut.

Interesting analysis! So, what would be your opinion on pinned hub + capture plate. Most vendors usually propose both at the same time. But, does it make sense to install both?

[Megator]

Originally Posted by NathObeaN

Interesting analysis! So, what would be your opinion on pinned hub + capture plate. Most vendors usually propose both at the same time. But, does it make sense to install both?

I wouldn't bother with the CBC if I had a pinned hub. Shouldn't hurt though as everything is already held via the pins/splines.

Personally I would add a dab of loctite when installing the pinned hub and call it a day.

[F87source]

Originally Posted by Megator

I wouldn't bother with the CBC if I had a pinned hub. Shouldn't hurt though as everything is already held via the pins/splines.

Personally I would add a dab of loctite when installing the pinned hub and call it a day.

I was literally going to say that lol. Except I'd use surface insensitive permatex medium strength blue thread locker, because of its surface insensitivity and ability to not be a torque multiplier. Or loctite 243 which does the same thing.

A bit of blue medium strength loctite/thread locker (not red or else you'll likely have to cut timing chains and split the block to pull the crank shaft in order to heat it to remove the crank bolt if you ever had to service an oil pump or timing chain related component).

Then I'd use torque seal or a colored sharpie as a witness mark on the crank bolt, which forms a small line that snaps if the crank bolt moves. This is a just in case thing.

[MadM2C]

lol Can't believe people are still arguing about this. WhAt FaCts Do YoU Have?

fact: there hasn't been any REPORTED spun crank hubs with a CBC installed.
fact: The quickest s55 m4 stock turbo 60-130 record is on a 60k mile m4 with stock crankhub and a CBC

fact: If youre a shop owner or work in parts sales, youre going to deny this.

[M2_MEDUSA]

Originally Posted by MadM2C

lol Can't believe people are still arguing about this. WhAt FaCts Do YoU Have?

fact: there hasn't been any REPORTED spun crank hubs with a CBC installed.
fact: The quickest s55 m4 stock turbo 60-130 record is on a 60k mile m4 with stock crankhub and a CBC

fact: If youre a shop owner or work in parts sales, youre going to deny this.

Exactly my point. I'll have CBC installed at the 1,200 mile mark soon as its back from break in service.

The rest of you enjoy being fear mongered into an unnecessary 3-4k hole in your wallet.

Fact: No spun hubs with a $100 part and 2 hours of labor.

Fact: many spun hubs with 1k part and 2k in labor.

Say what you want. One piece hubs are fear mongering marketing garbage. Only reason you need one is if your shooting bigger turbos. That's their absolute only purpose and need. If you don't ever plan on going big turbos. Waste of money.

[theblackdawnr3]

Originally Posted by SpecialEdition_F87

Exactly my point. I'll have CBC installed at the 1,200 mile mark soon as its back from break in service.

The rest of you enjoy being fear mongered into an unnecessary 3-4k hole in your wallet.

Fact: No spun hubs with a $100 part and 2 hours of labor.

Fact: many spun hubs with 1k part and 2k in labor.

Say what you want. One piece hubs are fear mongering marketing garbage. Only reason you need one is if your shooting bigger turbos. That's their absolute only purpose and need. If you don't ever plan on going big turbos. Waste of money.

Saying that there are more occurrences of failure than the other method without the taking into account the dramatically larger sample size and inherently flawed data collection method is fear mongering in and of itself. You're not bringing any information of value to the table.

As of now, I think the best plan is to save for any SCH when you're out of warranty, while you're in warranty. There was mention of a new BMW crank hub that fixes the issue in another thread on this forum. That may be the out we've been looking for.

[pz619]

Originally Posted by SpecialEdition_F87

Fact: No spun hubs with a $100 part and 2 hours of labor.

Fact: many spun hubs with 1k part and 2k in labor.

Say what you want. One piece hubs are fear mongering marketing garbage. Only reason you need one is if your shooting bigger turbos. That's their absolute only purpose and need. If you don't ever plan on going big turbos. Waste of money.

https://f80.bimmerpost.com/forums/sh...8&postcount=94

Your fact appears to be wrong based on this vendor, who carries a high reputation on these boards.

I do agree that the cost benefit probably says that CBC is the way to go, but to say that none failed simply is not representative of all cases. CBC dramatically reduces the risk.