[F87source]

Originally Posted by pz619

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.

Just like Megator who is also an engineer and tested diesel engines for failures, CBC adds no extra clamping force so friction based failures can still occur regardless.


Then you have to look at there being no concrete evidence that the crank bolt actually vibrates loose, which is really hard to believe since it is a small low mass nearly symmetrical object bolted directly to the crank snout (the center of rotation), torqued to an insanely high spec, and stretched in which makes it harder for a bolt to vibrate loose not to mention it is on an inline 6 engine which already is a low harmonics engine architecture. The only way I see it coming loose is if the hub spins and the friction between the hub and the bolt causes it to loosen. Also loosening of the bolt would more than likely cause a catastrophic engine failure due to the loss of clamping force making it easier to spin completely, and not just slip a few degrees which is what I think would be more likely due to just over coming friction.


The only way to prove it vibrating loose is with witness marks so you can see if it does loosen over time, but no one has ever done it.


Then you have to think what would happen if a CBC locked to the hub slips counter clockwise? Now you induce the risk of also loosening the crank hub during the slip, so that's going to be really bad news... This has been discussed not only by Megator and I, but by alot of other mechanical engineers on other forums. But that being said I do think this is a low risk even because I think the timing gear is more likely to slip on its own by over coming friction, rather than being able to spin the hub and the crank bolt too - there is no way there would be enough friction in the friction disk to do this.


So imo now that I had over a year to think about this, I probably would never put a CBC on my car ever.

[MyM2See]

Originally Posted by pz619

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.

Nice to hear Chris' take on this.

Kind of goes hand in hand why Carbahn offers warranty on their stage 1 tunes which dont come close to 600whp

[Talx]

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.

Fact, this is not a fact!

[F87source]

Originally Posted by Talx

Fact, this is not a fact!

I kept saying that....


Here's reality:

1) the chance of a spun crank hub is already really low

2) a majority of spun crank hub bmw owners aren't on the forums.

3) the chance of an owner being on the forum with a cbc and experienced a spun crank hub is low. Because it's a factor of 3 really improbable events having a cbc, being on the forum, and having a failure.

4) the chance of a stock car with a cbc is even lower because most stock guys don't mod, and most cbc owners have heavily modded cars.


So the probability of you seeing a stock car with a cbc reporting a failure on the forum is almost 0%. So saying it's a fact that the cbc is a guaranteed solution is statistically false.

The only way to say it's a fact is to have a proper control group and test group then determine via a chi squared test if the difference is statistically significant or sheerly due to chance. But that's impossible in this scenario, and the physics did of things still show that the friction disks can still be over come so the cbc is not a full solution, that much is clear unless your judgment is just deluded for a miracle solution due to fear of a pretty rare case of spinning your crank hub.


Imo if you're stock don't do anything let it spin (chances are it won't since it's pretty rare), and let warranty fix it for you.


Post warranty I'd still leave it stock sub 600 whp, at that power range spins are still rare and even if it does spin the chance it causes damage is so rare as well. So when it does spin get an upgraded hub, then add some blue loctite to the bolt and that guarantees there will be no vibrating loose (which is still unproven).


Personally I'd never get a cbc ever again even with an upgrade hub, I don't personally believe it does anything helpful. I believe it could add more detriments in that if the hub spins counter clockwise (again like I said earlier unlikely if the spin is timing chain induced because the friction disks likely can't exert that much force to the hub from the timing gears before it slips, but it can still happen if the serpentine belts exert the torque directly to the hub) then no you risk the cbc exacerbating the damage by loosening the crank bolt. Also every time the torque is exerted counter clockwise onto the hub it'll act like an impact wrench due to the high torque in a small time period, and if you have a cbc it'll transfer that impact effect to the crank bolt and over time can loosen the bolt. At least in theory that can happen.

So imo the added risks of a cbc is not worth it, especially since it is still unproven that the bolt vibrates loose.

[AmooManiak]

Originally Posted by F87source

I kept saying that....
Here's reality

I like the way you think.

[scflaw]

Originally Posted by F87source

I kept saying that....


Here's reality:

1) the chance of a spun crank hub is already really low

2) a majority of spun crank hub bmw owners aren't on the forums.

3) the chance of an owner being on the forum with a cbc and experienced a spun crank hub is low. Because it's a factor of 3 really improbable events having a cbc, being on the forum, and having a failure.

4) the chance of a stock car with a cbc is even lower because most stock guys don't mod, and most cbc owners have heavily modded cars.


So the probability of you seeing a stock car with a cbc reporting a failure on the forum is almost 0%. So saying it's a fact that the cbc is a guaranteed solution is statistically false.

The only way to say it's a fact is to have a proper control group and test group then determine via a chi squared test if the difference is statistically significant or sheerly due to chance. But that's impossible in this scenario, and the physics did of things still show that the friction disks can still be over come so the cbc is not a full solution, that much is clear unless your judgment is just deluded for a miracle solution due to fear of a pretty rare case of spinning your crank hub.


Imo if you're stock don't do anything let it spin (chances are it won't since it's pretty rare), and let warranty fix it for you.


Post warranty I'd still leave it stock sub 600 whp, at that power range spins are still rare and even if it does spin the chance it causes damage is so rare as well. So when it does spin get an upgraded hub, then add some blue loctite to the bolt and that guarantees there will be no vibrating loose (which is still unproven).


Personally I'd never get a cbc ever again even with an upgrade hub, I don't personally believe it does anything helpful. I believe it could add more detriments in that if the hub spins counter clockwise (again like I said earlier unlikely if the spin is timing chain induced because the friction disks likely can't exert that much force to the hub from the timing gears before it slips, but it can still happen if the serpentine belts exert the torque directly to the hub) then no you risk the cbc exacerbating the damage by loosening the crank bolt. Also every time the torque is exerted counter clockwise onto the hub it'll act like an impact wrench due to the high torque in a small time period, and if you have a cbc it'll transfer that impact effect to the crank bolt and over time can loosen the bolt. At least in theory that can happen.

So imo the added risks of a cbc is not worth it, especially since it is still unproven that the bolt vibrates loose.

This was really informative. Thanks

[F87source]

Originally Posted by scflaw

This was really informative. Thanks

It's mostly speculation and thought experiments on what would/could happen during a spun crank hub. If the hub itself does spin counter clockwise (there's a possibility it can because downshifts increase rpm of the hub and thus the inertia of the serpentine belt driven components will exrlert a counter clockwise torque directly to the hub which is also connected to the cbc now, but how much of a possibility idk - but I think most spins are due to the timing gear slipping) then a cbc is more if a detriment than a benefit.


But for now I'll personally steer clear of a cbc, because there is no proof of the crank bolt coming loose, even if there was a cbc still adds risk. Unless you had a pinned or splined hub then there never going to be a spin counter cclockwise so a cbc can never be detrimental in that case (need to clarify this because I was typing in a hurry in my original post I didn't make a new paragraph and clarify a cbc imo is more of a detriment on a stock hub so it looks like I'm saying it'll affect upgraded hubs too but it shouldn't because upgraded hubs don't spin), but I'd rather just use loctite to solve bolts vibrating loose instead of adding any mass to the crank shaft. Although it shouldn't be bad because it's symmetrical, right in the center of rotation, and very light - lighter than different dampers and flywheels on variations of these engines which would play more of an effect than this cbc.


Personally I'd get a hub upgrade in the event of a spin and that's really it.

[M2_MEDUSA]

Originally Posted by F87source

It's mostly speculation and thought experiments on what would/could happen during a spun crank hub. If the hub itself does spin counter clockwise (there's a possibility it can because downshifts increase rpm of the hub and thus the inertia of the serpentine belt driven components will exrlert a counter clockwise torque directly to the hub which is also connected to the cbc now, but how much of a possibility idk - but I think most spins are due to the timing gear slipping) then a cbc is more if a detriment than a benefit.


But for now I'll personally steer clear of a cbc, because there is no proof of the crank bolt coming loose, even if there was a cbc still adds risk. Unless you had a pinned or splined hub then there never going to be a spin counter cclockwise so a cbc can never be detrimental in that case (need to clarify this because I was typing in a hurry in my original post I didn't make a new paragraph and clarify a cbc imo is more of a detriment on a stock hub so it looks like I'm saying it'll affect upgraded hubs too but it shouldn't because upgraded hubs don't spin), but I'd rather just use loctite to solve bolts vibrating loose instead of adding any mass to the crank shaft. Although it shouldn't be bad because it's symmetrical, right in the center of rotation, and very light - lighter than different dampers and flywheels on variations of these engines which would play more of an effect than this cbc.


Personally I'd get a hub upgrade in the event of a spin and that's really it.

But data doesn't show any spun hubs under 600 with the CBC outside of money shifted cars. So yeah you make your argument but it lacks real data we've seen and companies who work with individuals outside of these forums express this. VTT to be exact.

Listen, follow the data. There have been quite a few high power pinned hubs that failed.

Spend the $100 and 2 hours of labor and you'll have data that backs up your investment stop fear mongering on the forums. No need for one piece with stock turbos. Waste of money and you'll be tearing your car apart just to get it done

[F87source]

Originally Posted by SpecialEdition_F87

But data doesn't show any spun hubs under 600 with the CBC outside of money shifted cars. So yeah you make your argument but it lacks real data we've seen and companies who work with individuals outside of these forums express this. VTT to be exact.

Listen, follow the data. There have been quite a few high power pinned hubs that failed.

Spend the $100 and 2 hours of labor and you'll have data that backs up your investment stop fear mongering on the forums. No need for one piece with stock turbos. Waste of money and you'll be tearing your car apart just to get it done

That's because there's not enough stock cars running a cbc, and then the rarity of the spun crank hub multiplied by the rarity of a stock car with a cbc makes it a near impossible event to observe. But that doesn't mean it can't happen.


You can't follow the data if it doesn't exist....

You need to look at the statistics...


Btw those are high powered applications that have failed pinned hubs, same argument can be made at stock power that they won't fail. But the reason we see failures of pinned hubs at high power levels is because there are so many of them at high power levels, the same cannot be said about stock cars with a cbc hence why we don't see anything.


I'm not fear mongering I'm being a realist, the statistics based on forum data simply (even if you go directly to a cbc manufacturer the customer might not report a spun crank hub even if it occured) aren't strong enough to conclude the cbc will be effective even at stock power levels. Next there has been zero evidence of the crank bolt vibrating loose, only speculation but no proof. Finally even the logic behind the cbc doesn't show any gains without the potential for exacerbating the issue, and if the vibration theory isn't true then it's useless.


If anything you are kind of spreading false hope in a potential solution of spun hub, due to your fear of it. You also started this thread with a bunch of bad ideas to solve the spun crank hub issue by recommending tightening the crank bolt every oil change - which a bad idea and worse than doing nothing (you can even fatigue the bolt by continually stretching it by retorquing it).



All in all I said what I believe, if there is hard facts with real data to prove I'm wrong I will happily retract my opinions and buy a cbc. But since the time it was released until now and on every forum I have seen there is the same talking points about why it is ineffective and how it can even be detrimental, and zero real evidence and data showing why it would be effective besides the statistically flawed argument of no spins are seen.

[F87source]

Originally Posted by SpecialEdition_F87

But data doesn't show any spun hubs under 600 with the CBC outside of money shifted cars. So yeah you make your argument but it lacks real data we've seen and companies who work with individuals outside of these forums express this. VTT to be exact.

Listen, follow the data. There have been quite a few high power pinned hubs that failed.

Spend the $100 and 2 hours of labor and you'll have data that backs up your investment stop fear mongering on the forums. No need for one piece with stock turbos. Waste of money and you'll be tearing your car apart just to get it done

Oh and I'm not trying to offend you or be rude or anything, I'm just trying to explain my point.

But my advice is for you to just enjoy your brand new m2c and not be too worried about the spun crank hub issues, they are so rare I personally wouldn't be too concerned. If you're stock just let the warranty take care of any issues, otherwise playing with a cbc could get your warranty denied and that wouldn't be good on a brand new car. Atleast drive it for a year to make sure you don't have any underlying issues first before modding it.

[GoneIn4Secs]

Even if you dont get an actual crank hub failure , your timing still gets skewed over time because of the high torque in the engine

The pieces are just held together to the crank with friction disks, like taking two sandpaper together and relying in the bolt to keep them stuck together and

Even with 'normal' spirited driving these two disks do shift from their factory alignment, generally you prob wont have it shift enough to catch a crankhub error in your dash, but the timing does go off the original calibration

I just think its kinda funny and silly that Mcars are designed to be driven harder than the usual road cars, and are even encouraged to do so, but they left such unnecessary achilles heel in the design of their flagship M engine, like how much extra would it have cost them to fabricate a solid piece?

Someone who is an engineer or somebody please educate me to the advantage or benefits of going with the design we ended up with

[AmooManiak]

I think this explains it pretty well why they did what they did.

[F87source]

Originally Posted by GoneIn4Secs

Even if you dont get an actual crank hub failure , your timing still gets skewed over time because of the high torque in the engine

The pieces are just held together to the crank with friction disks, like taking two sandpaper together and relying in the bolt to keep them stuck together and

Even with 'normal' spirited driving these two disks do shift from their factory alignment, generally you prob wont have it shift enough to catch a crankhub error in your dash, but the timing does go off the original calibration

I just think its kinda funny and silly that Mcars are designed to be driven harder than the usual road cars, and are even encouraged to do so, but they left such unnecessary achilles heel in the design of their flagship M engine, like how much extra would it have cost them to fabricate a solid piece?

Someone who is an engineer or somebody please educate me to the advantage or benefits of going with the design we ended up with

This is absolutely incorrect imo....

The crank position sensor and cam position sensor, is sensitive down to the degree or even greater (that's how you can see timing advances done in degree ranges even to a tenth of a degree - if it wasn't sensitive then you couldn't advance timing properly), that is the only way these engines can run at such high rpm and have valve to piston clearances as tight as they do, along with cam duration tuning and cam lift tuning that they perform without contact. So any movement and it will be detected. That's the only reason why you see full limp modes saving the S55's, those minor slips were caught before piston to valve contact was made. There is likely a small tolerance range, but any slips over time will be detected.


No your timing does not get skewed over time, this would imply that any car with this crank hub design (N52, N54, N55, S55) would have timing so far skewed at higher mileages that there would have been piston to valve contact. But we have not seen this at all so this cannot be the case. Even when the engines are taken apart for whatever reason, or the valve cover removed for cam shaft work there is no sign of timing being off.



At a high enough torque friction force between the disks, gears, and crank snout can be high enough that it is not a worry about the disks ever shifting, unless a high impulse torque event aka huge rpm increase in a short period of time causes the disks to shift (this is worse on the s55 because there is more inertia from all the extra stuff running off of the hub that needs to be sped up). But with friction disks they either slip or they don't there is no in between, because once that friction force is broken the first time the mating surfaces will be compromised and the coeffecient of friction will not be the same meaning subsequent slips are more and more common. This is why when you spin the hub you cannot just reset timing and reuse all the old components, they are done after every slip. So no they do not just slip or move over time from spirited driving, they slip or they don't.


The weakness was only really exposed on the S55 - my suspicion is that is has so much more inertial mass that must be driven by the crank hub + the dct providing such rapid down shifts especially with kick down. This is exacerbated by power, but I don't think power by itself is the cause because alot of high power n54's have not had an issue.


My second though on why they didn't fix this design is because they made a calculated decision that it would be cheaper to fix engines as they failed since the failure rates were so low, rather than just redesigning a part and doing a mass recall. This is what subaru did with the ring land failures.



In terms of the benefits of having the crank hub the way bmw did is that it makes it easier to install the timing chain. They should have added a key to the hub as well and that would have solved everything.

[F87source]

Here are some links to images of the friction disk: https://f80.bimmerpost.com/forums/sh....php?t=1702512
https://www.ecstuning.com/b-genuine-...0aAhZZEALw_wcB

Under such a high clamping load from the crank bolt being torqued to the rediculously high values that it is, the frictional forces on components sandwhiched to that friction disk is immense. Any movement that would occur by overcoming that frictional force would destroy that little disk and subsequent slips will be very very easy as the coefficent of friction from a damaged friction disk is drastically reduced due to the little grooves on it being damaged and smoothed out.

Essentially this means there are no micro slips or skewed timing events over time without the hub completely spinning shortly after. Since we see only cases of spun hubs or not (super rare to see spins in its own right) and we see no issues of timing calibration loss over time, there is no concern for timing skewing over time. It is imo an incorrect and misconceived notion.


Next the friction clamping mechanism is effective at such a high torque but not infallible, but since we see such low rates of spun crank hubs I would not be too worried - especially on an n55 with much less inertial mass that must be rotated by the crank hub, and of course less horse power (even if you tune you wouldn't need to worry too much as the m4 gts, m4 cs, and m2 cs already make much more power stock than the n55, so the n55 is essentially only catching up with a tune and those s55 engines even at the higher power levels of a gts model still don't experience crank hub slips at a higher rate the events are still rare).

[chris719]

Originally Posted by GoneIn4Secs

Someone who is an engineer or somebody please educate me to the advantage or benefits of going with the design we ended up with

Cost savings, design reuse. Either BMW did not catch this in R&D or they decided the failure rate was acceptable. The only people that know for sure won't be talking about it.

[F87source]

Originally Posted by chris719

Cost savings, design reuse. Either BMW did not catch this in R&D or they decided the failure rate was acceptable. The only people that know for sure won't be talking about it.

probably reuse, worked fined on the N54, worked fine on the N55, then issues on the S55. When they saw the problems they probably figured that it was cheaper to replace than reengineer and recall.

[MadM2C]

Originally Posted by F87source

That's because there's not enough stock cars running a cbc, and then the rarity of the spun crank hub multiplied by the rarity of a stock car with a cbc makes it a near impossible event to observe. But that doesn't mean it can't happen.


You can't follow the data if it doesn't exist....

You need to look at the statistics...


Btw those are high powered applications that have failed pinned hubs, same argument can be made at stock power that they won't fail. But the reason we see failures of pinned hubs at high power levels is because there are so many of them at high power levels, the same cannot be said about stock cars with a cbc hence why we don't see anything.


I'm not fear mongering I'm being a realist, the statistics based on forum data simply (even if you go directly to a cbc manufacturer the customer might not report a spun crank hub even if it occured) aren't strong enough to conclude the cbc will be effective even at stock power levels. Next there has been zero evidence of the crank bolt vibrating loose, only speculation but no proof. Finally even the logic behind the cbc doesn't show any gains without the potential for exacerbating the issue, and if the vibration theory isn't true then it's useless.


If anything you are kind of spreading false hope in a potential solution of spun hub, due to your fear of it. You also started this thread with a bunch of bad ideas to solve the spun crank hub issue by recommending tightening the crank bolt every oil change - which a bad idea and worse than doing nothing (you can even fatigue the bolt by continually stretching it by retorquing it).



All in all I said what I believe, if there is hard facts with real data to prove I'm wrong I will happily retract my opinions and buy a cbc. But since the time it was released until now and on every forum I have seen there is the same talking points about why it is ineffective and how it can even be detrimental, and zero real evidence and data showing why it would be effective besides the statistically flawed argument of no spins are seen.

There are literally no HARD facts on this topic at all though...

At which point you have to use common sense and make a decision based on your observations.

If you want to have your car completely taken apart and have someone drill into your crank, then by all means send it.