No popularity contest here. I've used the capture doesn't work ditched it run just the pinned hub and works good for me and I have access to the crank hub bolt if I need
Spun Crank Hub 6MT
- Thread starter SLOWESTN54
- Start date
You do not know for 100% fact that the bolt "vibrates" or whatever loose. You do not see when the hub spins. We only see the aftermath. You have ZERO proof of ANYTHING. If you have a video of a hub letting go and video of the bolt backing off little by little claiming that a CBC stops that, please post it.
Next, have you, or anyone here even considered that bolts do in fact stretch.
If a crank bolt stretches, even with a CBC, guess what happens ? Hub WILL slip AND bolt captured will be loose along with hub and pulley / dampner, etc.
Many would assume the bolt backed off due to a force or vibration when it could simply be a loss of clamping force due to bolt stretching / fatigue.
In any case the scenario I presented.....the CBC still would not do jack shit to stop this.
If I were paranoid enough, I would invest in a new bolt and friction discs before a CBC.
And yes...it's that simple
Its your engine and do as you wish and no one is telling you how to run it, it all should be laid out
for people to see and make their own judgment from the info provided.
In the end when it all goes south if it does, one has no one to blame but themselves and no one is
holding a gun to your head telling you must run it.
So your basically telling me there is no benefit from running a CBC ?
Tell that to BMW as you must know something they don't and you should educate them like you are
trying to do here.
Well it's common knowledge amongst engine builders that these items are one time use and should be replaced when rebuilding one.
I replaced my friction disk, hub with a spline lock, bolt and added a CBC for extra protection, 3 years on with no failure but have managed to blow 3 x 3rd gears and 2 diffs and not from abuse and if it survived that it will last till I need to rebuild the engine when it finally wears out one day.
The bolt will not stretch as it's not like a head bolt as the only force on it is horizontal to the thread and not vertical so it works on shear strength.
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Yes I will do as I please.
No, to me the CBC is worthless.
Bmw ? Please, they are the ones that came up with this shit design that everyone agrees is a SHIT design , yet you rely on them adding a factory cbc to another engine as the holy grail of why I or others should run one ?
LOL !!
Yes, I know enough to know that BMW fucked up. I don't need to call them and educate them on that part. They know it as well I am sure.
To make it clear, I DO NOT AND WILL NOT USE A CBC.
You and others can do what you want.
Get off VTTs dick already man.
As I already said there is others around you don't have to use VTT so I don't know why you got your panties in a twist.
Well the s65 uses the same hub design as the n54 as well as the f80.
You seen a few stock f80's spin a crank hub and the only difference is CBC, draw your own conclusions.
But I can tell you I've seen plenty of modified ones and an educated guess why BMW uses this design is to deny warranty, as its designed
to slip under high powered applications so BMW can make money from engine sales or repairs as there is not much money in car sales.
The money is in aftersales, industry well known knowledge.
Seems to me a bare minimum might actually be the CBC combined with the updated sprocket and hub assembly (2019) which BMW put out. It's only $200 if memory serves and bolts right up.
Serious questions:
1. What proportion of n54's on the road with stock oem crank hub configuration have spun a hub?
2. What proportion on n54's on the road with cbc (but no pinning, keying, etc.) have spun a hub?
I concede those questions are biases, as most of the first population are not modified or abused, while the second population is likely close to 100% highly modified and routinely beat on.
But the point is you can't prove something won't happen. The best you can do is keep increasing your sample size to improve confidence that it won't happen, you won't get to 100% confidence.
Similarly, running CBC for 3 years without issue doesn't prove cbc works, because for all you know, you may have ran those 3 years without CBC and still had no issues.
Conversly, people HAVE ran CBC and spun a hub. I'm not sure how many CBC systems have been sold and installed, but its surly < < than the number of modified and beat on n54's without CBC installed. And I think it's safe to say that most of those non-CBC n54's have NOT spun a hub.
The fact that BMW engineers have incorporated a CBC system into an engine doesn't prove CBC works. I'm an engineer, and trust me, we make mistakes too. We may accidentally overlook some phenomena, or often in reality things just flat out don't work like we expect due to some effect we've never considered. Or maybe we just plain get lazy and don't start with a basic free body diagram when analyzing the forces acting on a system. Hell, NASA meteor'd a Mars lander into the red planet because they mixed units without converting. There may be a similar reason there is a BMW engine designed with a CBC system, I can't say because I wasn't involved in its design. I am curious though, how many BMW engines incorporate this design from the factory? If it's just 1 or 2, that may support that they realized CBC without some other means of locking the hub to the crank doesn't work. Especially since they've acknowledged the shortcomings of the current design, as evidenced bu their release of a revised version with larger friction bearing surfaces (and no CBC).
1. What proportion of n54's on the road with stock oem crank hub configuration have spun a hub?
2. What proportion on n54's on the road with cbc (but no pinning, keying, etc.) have spun a hub?
I concede those questions are biases, as most of the first population are not modified or abused, while the second population is likely close to 100% highly modified and routinely beat on.
But the point is you can't prove something won't happen. The best you can do is keep increasing your sample size to improve confidence that it won't happen, you won't get to 100% confidence.
Similarly, running CBC for 3 years without issue doesn't prove cbc works, because for all you know, you may have ran those 3 years without CBC and still had no issues.
Conversly, people HAVE ran CBC and spun a hub. I'm not sure how many CBC systems have been sold and installed, but its surly < < than the number of modified and beat on n54's without CBC installed. And I think it's safe to say that most of those non-CBC n54's have NOT spun a hub.
The fact that BMW engineers have incorporated a CBC system into an engine doesn't prove CBC works. I'm an engineer, and trust me, we make mistakes too. We may accidentally overlook some phenomena, or often in reality things just flat out don't work like we expect due to some effect we've never considered. Or maybe we just plain get lazy and don't start with a basic free body diagram when analyzing the forces acting on a system. Hell, NASA meteor'd a Mars lander into the red planet because they mixed units without converting. There may be a similar reason there is a BMW engine designed with a CBC system, I can't say because I wasn't involved in its design. I am curious though, how many BMW engines incorporate this design from the factory? If it's just 1 or 2, that may support that they realized CBC without some other means of locking the hub to the crank doesn't work. Especially since they've acknowledged the shortcomings of the current design, as evidenced bu their release of a revised version with larger friction bearing surfaces (and no CBC).
I'm not convinced it has to do with power level. I haven't independently confirmed, but regard crank rotation, doesn't increasing rpm put a tightening torque on the bolt? If so, then slowing engine rpm would apply a loosening torque to the bolt. In the ghasden thread, he said it spun when the wheels hooked up after a burn out. What happens when your wheels hook up? Engine rpm quickly drops (applying a loosening torque to the bolt, no?). The quicker the rpm drop, the greater the loosening torque on the bolt.
I wonder how many stock n54's have spun the hub? I bet we wouldn't hear about them, as the majority of n54 owners are probably regular people, and not on the forums. But BMW would hear about them. If it was just enthusiasts spinning hubs, it probably wouldn't be a big enough problem for bmw do decide to update the design. The fact they uodated it (at least to me) suggests that average, non-modified n5x engines are having this problem at an unacceptable rate.
It's also interesting that it seens predominantly on cars with MT vs. AT. Though it may make sense, as you can't really drop the clutch (and slow engine rpm super quickly) on an AT like you can on MT.
Has anybody heard of this happening on an AT car yet?
I wonder how many stock n54's have spun the hub? I bet we wouldn't hear about them, as the majority of n54 owners are probably regular people, and not on the forums. But BMW would hear about them. If it was just enthusiasts spinning hubs, it probably wouldn't be a big enough problem for bmw do decide to update the design. The fact they uodated it (at least to me) suggests that average, non-modified n5x engines are having this problem at an unacceptable rate.
It's also interesting that it seens predominantly on cars with MT vs. AT. Though it may make sense, as you can't really drop the clutch (and slow engine rpm super quickly) on an AT like you can on MT.
Has anybody heard of this happening on an AT car yet?
I've yet to hear it happening to a auto car. My car was a manual making pretty decent power and weighing a decent amount. Same as @slowest54 he was a manual on twins. Mine spun in 3rd gear can't remember about slowest
Rather than throwing insults and opinions over and over how about we focus on information at hand?
So 2019 BMW came up with a new S55 (and N54) hub solution. My question would be to @martymil - any idea why BMW chose not to include a CBC solution (for example as they did for S65)? I find that somewhat curious.
BMW makes mistakes ... if one is not an engineer or significantly built stuff in your life, one doesn't know anything about this works. If one has done either, then one is cluess - I would never hire that person. Simply, mistakes are made. BMW has made updates on countless designs over the years - like any engineering org.
Why has BMW not provided a CBC solution along with the updated sprocket?
So 2019 BMW came up with a new S55 (and N54) hub solution. My question would be to @martymil - any idea why BMW chose not to include a CBC solution (for example as they did for S65)? I find that somewhat curious.
BMW makes mistakes ... if one is not an engineer or significantly built stuff in your life, one doesn't know anything about this works. If one has done either, then one is cluess - I would never hire that person. Simply, mistakes are made. BMW has made updates on countless designs over the years - like any engineering org.
Why has BMW not provided a CBC solution along with the updated sprocket?
Never heard a n54 auto spinning a hub unless second hand parts where reused during a rebuild.
N54's,with stock clutch is also highly unlikely.
Now where I've seen failures are, which includes F series
DCT is quite common in high power applications across e and f platforms.
Manuals fitted with single mass flywheels and/or twin plate clutches where dropping the clutch or lightning fast gear changes can put an abnormal stress on the hub due to abrupt rpm changes.
N54's,with stock clutch is also highly unlikely.
Now where I've seen failures are, which includes F series
DCT is quite common in high power applications across e and f platforms.
Manuals fitted with single mass flywheels and/or twin plate clutches where dropping the clutch or lightning fast gear changes can put an abnormal stress on the hub due to abrupt rpm changes.
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The most likely reason is to deny warranty on modified BMW's as I stated earlier, most manufactures don't make much money on car sales but killer mark-ups on after sales and repairs.
Interesting that's its (more) common on DCT, I think that seems like a clue. DCT's change gears much faster than AT, which means the engine must drop rpm much faster (than AT) to engage the next gear. Faster rpm drop equals more loosening torque on the bolt (via rotational intertia of the hub, bolt, and valve train).
Edit: When I say more loosening torque on the bolt, I mean in the whole hub and bolt. I.e. the hub is negatively accelerating in the direction of trying to unscrew the bolt.
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Fair question.
Happened to burger motor sports employees wife's car making 700 hp through an auto i guess there's a thread on n54 tech bout it
Did they mention if/what transmission flash they were running? The thought had occured to me that if very quick and abrupt engine deceleration is the driving force spinning the hub, then more aggressive shifting through transmission flashes could potentially make spinning the hub more likely.
I was going to mention this....especially the last part but....pointless to argue with certain individuals.
So BMW adds a factory CBC because they know there is a problem.
Bmw also adds a new redesigned friction disc to an engine they know has a problem.
Why CBC one and not the other ?
To deny warranty claims and keep hubs spinning .
Makes perfect sense now
Yes it has been said the engine abrupt deceleration causes this.
Guess what ? Even with a CBC it can and has happened.
The more rotating mass that bolt must hold, the easier it is to back that bolt out when abrupt deceleration comes into play.
Put a 100lb balancer and pulley on it. See how fast that bolt backs out on a downshift. Locking that bolt to the driving force once again, does nothing to prevent it from loosening.
@RuskiRacer has proven it can and does in fact still happen (failure) with a CBC.
As said above, can anyone prove the cbc does work ?
No because any engine with CBC that has not spun a hub may have never spun it to begin with
Proof vs no proof
/thread.
