Crank Hub Question

[saint80]

Ok, so I've done a few modifications to my f80 and have learned about this OEM crank hub issue. I don't understand it all, but what I do understand is that when we add more HP to the OEM crank hub, it becomes more likely to fail.

My question is this - With a Stage 1 tune, Stone full exhaust, and running E85 - Do I need to worry about replacing the crank hub, or do I only need to worry about this if I add even more power to the car.

You guys are the genius's, so I figured best to ask here. Thanks ahead of time for the help!!!

[b_w.]

are you running a stage 1 tune or an e85 tune?

[theweebabySeamus]

Originally Posted by b_w.

are you running a stage 1 tune or an e85 tune?

^ need more clarity on e85 amount. Are you running a full e85 file or a basic stage 1 with a splash of e85? They're very different

[saint80]

The BM3 Multi-map allows for e85 and stage 1, as I understand it. I haven't run full e85, or any mixture yet, just inquiring in general for what to watch for and or what I need. Right now, the car is in the Multi-map stage 1 tune.

[b_w.]

Probably fine but always rolling the dice with a tune.

[M 4 FUN]

You never add more power to the crank hub. The power goes to the prop shaft and rear axle, then the wheels. That's where you have the load in the drivetrain, not on the cam drive system. NOTHING is heavier to rotate or creates more resistance to turn around in the cam drive and oil pump system just because you have more power. If you would change to tougher valve springs, then you would have more resistance.

[saint80]

Originally Posted by M 4 FUN

You never add more power to the crank hub. The power goes to the prop shaft and rear axle, then the wheels. That's where you have the load in the drivetrain, not on the cam drive system. NOTHING is heavier to rotate or creates more resistance to turn around in the cam drive and oil pump system just because you have more power. If you would change to tougher valve springs, then you would have more resistance.

Thank you!!

[FrankMstein]

Originally Posted by M 4 FUN

You never add more power to the crank hub. The power goes to the prop shaft and rear axle, then the wheels. That's where you have the load in the drivetrain, not on the cam drive system. NOTHING is heavier to rotate or creates more resistance to turn around in the cam drive and oil pump system just because you have more power. If you would change to tougher valve springs, then you would have more resistance.

I have never understood that people don't understand that adding power...adds force to the hub and increasing its propensity to spin. I never thought that people think that and I have to do better about putting myself in the place of the average ABuser. I like your perspective and further convinces me it is more user error than anything else. You should post this over on the master CH post.

https://f80.bimmerpost.com/forums/sh....php?t=1560274

nalinc23

[M 4 FUN]

Originally Posted by FrankMstein

I have never understood that people don't understand that adding power...adds force to the hub and increasing its propensity to spin. I never thought that people think that and I have to do better about putting myself in the place of the average ABuser. I like your perspective and further convinces me it is more user error than anything else. You should post this over on the master CH post.

https://f80.bimmerpost.com/forums/sh....php?t=1560274

nalinc23

Well, i have tried to explain this to a lot of people but people are so convinced of what they have read on the forums over the years that they can't really think that what i say is right. What amazes me most is that it seems like people don't really understand how it works technically because when i ask for a good technical explanation to how the load of the cam drive system can increase i never get a proper explanation.
The thing is that it actually can take load off the cam drive system because when you tune the car you get more power at lower revs so there is no need to rev the engine as much to get the same performance. What is tougher on the cam drive system is high rpm, not a tune.
The only thing i see that loads up the cam drive/ oil pump system is that the S55 engine has more resistance in the oil pump as it has one regular oil pump and also a suction pump that is driven from the same gear. This does not a N54 have for example.

[b_w.]

Originally Posted by FrankMstein

I have never understood that people don't understand that adding power...adds force to the hub and increasing its propensity to spin. I never thought that people think that and I have to do better about putting myself in the place of the average ABuser. I like your perspective and further convinces me it is more user error than anything else. You should post this over on the master CH post.

https://f80.bimmerpost.com/forums/sh....php?t=1560274

nalinc23

Been a while since I studied physics in high school but I do recall that force equals mass x acceleration. I would assume that adding a tune and more power increases the acceleration of the engine and therefore the force that is put on the crankhub to get the valve train and timing components moving under hard acceleration....

[wheela]

Originally Posted by M 4 FUN

Well, i have tried to explain this to a lot of people but people are so convinced of what they have read on the forums over the years that they can't really think that what i say is right. What amazes me most is that it seems like people don't really understand how it works technically because when i ask for a good technical explanation to how the load of the cam drive system can increase i never get a proper explanation.
The thing is that it actually can take load off the cam drive system because when you tune the car you get more power at lower revs so there is no need to rev the engine as much to get the same performance. What is tougher on the cam drive system is high rpm, not a tune.
The only thing i see that loads up the cam drive/ oil pump system is that the S55 engine has more resistance in the oil pump as it has one regular oil pump and also a suction pump that is driven from the same gear. This does not a N54 have for example.

I generally agree with this, but... I don't have any data to point to backing this up, but I think crank twist could be a factor, as well as cylinder pressure, both of which increase with higher power.

Crank twist - With each power stroke, the piston pushing creates torque on the crank shaft that's resisted by the drivetrain. The torque will cause twist in the crank shaft. That twist will relieve when the exhaust valves open, releasing cylinder pressure. The release could be a bit of a rotational shock load on the crank hub, depending how high cylinder pressure is, and how quickly the cylinder pressure relieves when the exhaust valves open. The more torque you're able to create, the more twist in the crank, and therefore more twist to release between power strokes. I think the release is most violent with lower rpm (lugging engine), as there isn't as much rotational momentum in the crank shaft to keep its speed up between power strokes, and more time between power strokes for the twist to release. I suspect releasing of this twist between power strokes could be pretty hard on the crank hub joint, especially if you're lugging the engine, or running really high torque.

Also with higher torque, the cylinder pressures will be higher. Higher cylinder pressure means more force needed to push the exhaust valves open against cylinder pressure. This higher force equals more rotational torque required from the valvetrain. Again, probably more of a factor at lower rpm with less rotational momentum in the valve train to help that initially cracking open of the exhaust valves.

Are these significant factors? I don't know. But they seem plausible to me.

[wheela]

Here's another good thread for crankhub info:

https://f80.bimmerpost.com/forums/sh....php?t=1226184

[n8dgr84]

Mine was ok on Stage 1 then spun on E60 custom tune.

Good luck!

[M 4 FUN]

Originally Posted by b_w.

Been a while since I studied physics in high school but I do recall that force equals mass x acceleration. I would assume that adding a tune and more power increases the acceleration of the engine and therefore the force that is put on the crankhub to get the valve train and timing components moving under hard acceleration....

Then you know that the engine accelerates fastest when you just stand still and blip the throttle or do a downshift in the wrong gear and release the clutch.
A tune has nothing with this to do.

[M 4 FUN]

Originally Posted by wheela

I generally agree with this, but... I don't have any data to point to backing this up, but I think crank twist could be a factor, as well as cylinder pressure, both of which increase with higher power.

Crank twist - With each power stroke, the piston pushing creates torque on the crank shaft that's resisted by the drivetrain. The torque will cause twist in the crank shaft. That twist will relieve when the exhaust valves open, releasing cylinder pressure. The release could be a bit of a rotational shock load on the crank hub, depending how high cylinder pressure is, and how quickly the cylinder pressure relieves when the exhaust valves open. The more torque you're able to create, the more twist in the crank, and therefore more twist to release between power strokes. I think the release is most violent with lower rpm (lugging engine), as there isn't as much rotational momentum in the crank shaft to keep its speed up between power strokes, and more time between power strokes for the twist to release. I suspect releasing of this twist between power strokes could be pretty hard on the crank hub joint, especially if you're lugging the engine, or running really high torque.

Also with higher torque, the cylinder pressures will be higher. Higher cylinder pressure means more force needed to push the exhaust valves open against cylinder pressure. This higher force equals more rotational torque required from the valvetrain. Again, probably more of a factor at lower rpm with less rotational momentum in the valve train to help that initially cracking open of the exhaust valves.

Are these significant factors? I don't know. But they seem plausible to me.

I agree with that the resistance is in the drivetrain. But i disagree that the higher torque would be a factor. The only thing that can make the bolt come loose would be extremely fast rev changes that creates a shock in the cam drive system. This chock never happens when the engine is in gear as it revs up so slowly. But if you do a money shift it's another thing, or stand at the dragstrip with sticky tires and uprated clutch and rev the engine and dump the clutch. Again, this has nothing with a tune to do.

[FrankMstein]

Originally Posted by M 4 FUN

Then you know that the engine accelerates fastest when you just stand still and blip the throttle or do a downshift in the wrong gear and release the clutch.
A tune has nothing with this to do.

This is what is known as a mic drop.

"or do a downshift in the wrong gear and release the clutch." and quickly remove your foot at 6k rpm, kickdown, getting both tires off the ground under hard acceleration or deceleration...all shocks to the CH system.

Put yourself in place of the CH and consider all the factors that influence it moving. I have spoken extensively on this over on the other thread. I have looked at the data and there is no conclusive data that proves extra power = CH spin. It indicates abuse when stock power has the propensity. Tuned people abuse their cars more a lot of them don't even warm them up before said abuse hmmmmm.

[wheela]

Originally Posted by M 4 FUN

You never add more power to the crank hub. The power goes to the prop shaft and rear axle, then the wheels. That's where you have the load in the drivetrain, not on the cam drive system. NOTHING is heavier to rotate or creates more resistance to turn around in the cam drive and oil pump system just because you have more power. If you would change to tougher valve springs, then you would have more resistance.

I used to think the same thing when I first heard about crank hub failures in n54 & n55. I didn't beleive it had anything to do with power level. I thought it was just abuse. But after seeing so many more occurrences in s55, I started giving it more thought too see if I could have been missing something. I currently suspect it's probably more to do with variability in the friction disks (detail of my thoughts about the disks are over in that thread I linked to, page 11 I think?). But also after more thought, I can see a couple mechanisms that could increase loading on the hub as torque increases.

Above you mention tougher valve springs can add resistance. This is absolutely true. But so does cylinder pressure. Attached is a screenshot from a thread where a guy was trying to figure out mechanical loading on a cam. The general engineering consensus is the 3 primary forces are 1. Valve spring, 2. Inertial forces that increase with rpm, and 3. Cylinder pressure which increases with load. The force from cylinder pressure will drop as the exhaust valve opens and the cylinder de-pressurizes, but the force to open the valve against the cylinder pressure must still be overcome by the valve train. If you tune the engine to the point where you're doubling the torque output, you can safely assume you're also roughly doubling the cylinder pressure. If you're doubling the cylinder pressure, you're doubling the force it's applying against the exhaust valve trying to hold it shut.

Is it enough extra force to increase likelihood of spinning a hub? I don't know. But it's certainly a force the valve train has to overcome which increases with power level. Which is something that wasn't obvious to me about crank hub spinning at first glance.

[wheela]

Originally Posted by M 4 FUN

I agree with that the resistance is in the drivetrain. But i disagree that the higher torque would be a factor. The only thing that can make the bolt come loose would be extremely fast rev changes that creates a shock in the cam drive system. This chock never happens when the engine is in gear as it revs up so slowly. But if you do a money shift it's another thing, or stand at the dragstrip with sticky tires and uprated clutch and rev the engine and dump the clutch. Again, this has nothing with a tune to do.

I agree with this. The only point I add is related to crank twist. Maybe better to call it harmonics. Torque will add twist in the crank. The torque isn't constant through an engine rotation, it pulses with the power strokes. This is how you're able to detect misfires, the DME can see if a torque pulse is missing via crank position sensor not detecting rotational acceleration when a cylinder is supposed to fire. If you tune an engine up to double the torque, you're doubling the amplitude of crank twist. It's the harmonic balancers job to try and dampen these pulses out. But with doubling the amplitude it has to dampen, it's extra rotational load placed on the harmonic balancer and the entire valve train. The crank hub is what's withstanding that loading. With 3 power strokes per engine rotation, that can be a lot of rotational pounding on the crank hub joint.

So again, I don't know if it's enough extra loading to increase likelihood of the crankhub spinning, but it's clear to me that this is loading on the crank hub joint that will increase as the motor is tuned to make more torque.

[FrankMstein]

Yet no discussion on warming the components to operating temp before beating...

[wheela]

Originally Posted by FrankMstein

Yet no discussion on warming the components to operating temp before beating...

Not sure if the sarcasm is directed at me?. You already mentioned people beating up on their cars, and abusing them before warming them up. I don't, and didn't dispute any of that, and don't feel there is any need to explain how those activities can contribute to the issue.

It was previously noted in the thread that nobody has been able to explain how a higher power tune can add more loading to the crank hub joint. In the interest of advancing understanding of the issue, I presented technical explanations of two ways adding more power via a tune will add more loading to the crank hub joint. I qualified both explanations with acknowledgment that I don't know magnitude of the affects, or if they are significant enough to increase likelihood of a spun crankhub if running higher power.

That said, if somebody can provide a convincing technical explanation why what I've presented is incorrect, and these things don't actually increase loading of the crank hub as power is increased, I'm certainly eager to hear it and further the discussion

[M 4 FUN]

Originally Posted by wheela

I used to think the same thing when I first heard about crank hub failures in n54 & n55. I didn't beleive it had anything to do with power level. I thought it was just abuse. But after seeing so many more occurrences in s55, I started giving it more thought too see if I could have been missing something. I currently suspect it's probably more to do with variability in the friction disks (detail of my thoughts about the disks are over in that thread I linked to, page 11 I think?). But also after more thought, I can see a couple mechanisms that could increase loading on the hub as torque increases.

Above you mention tougher valve springs can add resistance. This is absolutely true. But so does cylinder pressure. Attached is a screenshot from a thread where a guy was trying to figure out mechanical loading on a cam. The general engineering consensus is the 3 primary forces are 1. Valve spring, 2. Inertial forces that increase with rpm, and 3. Cylinder pressure which increases with load. The force from cylinder pressure will drop as the exhaust valve opens and the cylinder de-pressurizes, but the force to open the valve against the cylinder pressure must still be overcome by the valve train. If you tune the engine to the point where you're doubling the torque output, you can safely assume you're also roughly doubling the cylinder pressure. If you're doubling the cylinder pressure, you're doubling the force it's applying against the exhaust valve trying to hold it shut.

Is it enough extra force to increase likelihood of spinning a hub? I don't know. But it's certainly a force the valve train has to overcome which increases with power level. Which is something that wasn't obvious to me about crank hub spinning at first glance.

Yes, cylinder pressure increases on two valves at a time but as the engine spins at such a high speed and the camshaft is rotating at a linear speed or accelerates relatively slow under engine load i can't see that this would chock the crankhub. The engine revs are still very constant or increasing very slow compared to a money shift or dropping the clutch at high rpm's. What i mean is that the crankhub doesn't know if the cylinder pressure is high.
The force is not double as it's only one cylinder at a time that is in the compression stroke and five more that rotates and still push all the other valve springs. Only two of 24 valves have a bit more resistance.

[M 4 FUN]

Originally Posted by wheela

I agree with this. The only point I add is related to crank twist. Maybe better to call it harmonics. Torque will add twist in the crank. The torque isn't constant through an engine rotation, it pulses with the power strokes. This is how you're able to detect misfires, the DME can see if a torque pulse is missing via crank position sensor not detecting rotational acceleration when a cylinder is supposed to fire. If you tune an engine up to double the torque, you're doubling the amplitude of crank twist. It's the harmonic balancers job to try and dampen these pulses out. But with doubling the amplitude it has to dampen, it's extra rotational load placed on the harmonic balancer and the entire valve train. The crank hub is what's withstanding that loading. With 3 power strokes per engine rotation, that can be a lot of rotational pounding on the crank hub joint.

So again, I don't know if it's enough extra loading to increase likelihood of the crankhub spinning, but it's clear to me that this is loading on the crank hub joint that will increase as the motor is tuned to make more torque.

I understand how you think. The question is if the increased torque twist is in the small area at the crank hub bolt or if it is at the whole length of the crank where the the load from the rods are . I can't see how the crank can twist at the short end of the crank as there is no extra force there. Everything is still rotating at the same speed and nothing gives more resistance in the cam drive system, just like when stock, nothing is changed.

But there is one thing that creates more resistance on the crankhub on the S55 engines than on the N54/55 engines but noone ever mention that. Guess what it is .