[Tricki]

Originally Posted by F87source

If the slip is minor and the crank position sensor catches it in time and triggers a limp mode yes to an extent. Adjusting timing is easy if you have the super expensive BMW tools and the know how, otherwise it'll probably be pretty expensive for a shop to do it.

If it slips too aggressively and the pistons hits the head worst case scenario you'll need a new motor, best case scenario just a new valve.

+1

You can also get a kick down blocker to stop kick downs as well to help alleviate the possibility of spinning the hub.

Is the issue on the kickdown when accelerating or the downshift when decelerating?

[F87source]

Originally Posted by Tricki

Is the issue on the kickdown when accelerating or the downshift when decelerating?

From what I know this issue can happen at any instance when there is load on the hub. However it is highly unlikely (pretty much zero, unless your hub was already on the verge of spinning) to happen during conditions of low stress like idling and cruising, compared to heavy stresses like the dct kick down which drops a few gears in an instant.

But to answer your question it's the kick down when accelerating. If you press down on your pedal you can feel a really linear travel to the floor, then the last couple of mm you feel a little click or point of higher resistance where if you press a bit harder you can feel the pedal give just a bit more. When the pedal passes that point upon full throttle acceleration it will drop a few gears depending on rpm etc, initiating a kick down. This is what causes alot of stress on the hub and is the most common or attributed cause of the hub slipping.


Decelerating and downshifting does put stress on the hub, but if you do it a gear at a time (give it a bit to rev up and slowly decline in rpm like you'd do in a manual) the stresses shouldn't be high enough to spin the hub, as shown on the n54 and n55 where spun hubs are essentially unheard of.


If you have a manual for example and go from 6th gear at 1500 rpm and shift it directly to 4th and dump the clutch it would probably be the same stress as a kick down.

[armiii]

Originally Posted by F87source

From what I know this issue can happen at any instance when there is load on the hub. However it is highly unlikely (pretty much zero, unless your hub was already on the verge of spinning) to happen during conditions of low stress like idling and cruising, compared to heavy stresses like the dct kick down which drops a few gears in an instant.

But to answer your question it's the kick down when accelerating. If you press down on your pedal you can feel a really linear travel to the floor, then the last couple of mm you feel a little click or point of higher resistance where if you press a bit harder you can feel the pedal give just a bit more. When the pedal passes that point upon full throttle acceleration it will drop a few gears depending on rpm etc, initiating a kick down. This is what causes alot of stress on the hub and is the most common or attributed cause of the hub slipping.


Decelerating and downshifting does put stress on the hub, but if you do it a gear at a time (give it a bit to rev up and slowly decline in rpm like you'd do in a manual) the stresses shouldn't be high enough to spin the hub, as shown on the n54 and n55 where spun hubs are essentially unheard of.


If you have a manual for example and go from 6th gear at 1500 rpm and shift it directly to 4th and dump the clutch it would probably be the same stress as a kick down.

Would you recommend not to use kick down?

[F87source]

Originally Posted by armiii

Would you recommend not to use kick down?

Yeah I would avoid it, you can buy a kick down blocker that prevents the pedal from entering the kick down range. This way you can slam the throttle into WOT position without worry.

[doughboy]

Out of sympathy for any powerful car i wouldn't use kickdown. Too stressful on the drivetrain.

[1mm2]

Originally Posted by doughboy

Out of sympathy for any powerful car i wouldn't use kickdown. Too stressful on the drivetrain.

Yup, not worth it...

[F87source]

Originally Posted by doughboy

Out of sympathy for any powerful car i wouldn't use kickdown. Too stressful on the drivetrain.

Yes for the s55, not really true for other cars without the crank hub issue. The m2C only makes 400whp and there are plenty of more powerful cars (gtr, f90 m5, Audi r8, audi ttrs etc) that can utilize the kick down all day long without issue.

Sure it's stressful for the drivetrain but it is factored into the overall equation when engineers design the car, so it should be a non issue at stock power levels, with the exception in this case being the s55 since the hub is a known issue.

[Tricki]

Originally Posted by F87source

Yes for the s55, not really true for other cars without the crank hub issue. The m2C only makes 400whp and there are plenty of more powerful cars (gtr, f90 m5, Audi r8, audi ttrs etc) that can utilize the kick down all day long without issue.

Sure it's stressful for the drivetrain but it is factored into the overall equation when engineers design the car, so it should be a non issue at stock power levels, with the exception in this case being the s55 since the hub is a known issue.

Honestly it should be ok for whatever HP is....GTS is 500hp.
If i tune the 500hp map and the Hub fails can BMW then say it's because the car is tuned when they have a GTS with the same s55 engine with the same Hub 🤷🏽*♂️

[F87source]

Originally Posted by Tricki

Honestly it should be ok for whatever HP is....GTS is 500hp.
If i tune the 500hp map and the Hub fails can BMW then say it's because the car is tuned when they have a GTS with the same s55 engine with the same Hub 🤷🏽*♂️

Yeah it should never spin in the first place, but it was a design that bmw chose to make the assembly of the motor + timing chain easier.

Keep in mind the GTS is also at risk of spinning the hub too, there is nothing special about it that prevents the crank hub from failing.

Yes if you tune the car bmw can deny warranty if the hub fails, they can make the argument that the gts was factory tune and had parts like water injection etc that was designed to support the power and the m2C does not which is why the failure occured and there is pretty much nothing you can do.

[cheveux]

Originally Posted by F87source

You have to retorque the crank bolt before you put on the CBC so it won't matter if it got a bit loose (a nm less etc. Otherwise if it did get too lose your hub would've slipped) as long as the friction disc didn't slip which means the hub didn't move. The bolt just sandwiches the whole assembly, whether or not it is in the correct position shouldn't really matter so long as the hub itself doesn't move.

I guess it's up to the end user what they do but for me if the bolt slipped and BMW saw that CBC they would probably have reasonable grounds to deny warranty.


1) it's actually quite a rare issue.
2) if it isn't happening frequently enough it is cheaper to fix motors as they go vs. perform a recall. Just like on the sti with ring land failure.
3) the CBC isn't a complete fix, the friction disc can still spin.



+1

Retorque the crank bolt?? i thought the bolt was one use/one time torque only and could not be retorqued if not new!

[doughboy]

Originally Posted by cheveux

Retorque the crank bolt?? i thought the bolt was one use/one time torque only and could not be retorqued if not new!

Yes, correct, you absolutely cannot touch the centre bolt at all.

It is a single use TTY stretch bolt, so it doesn't even have a final torque setting.

On a new assembly, you torque it to 120nm then turn it a further 270degrees, which will probably be over 500nm+ but you will never know .

BMW TIS notes warn you'll need over 600nm to undo it.

[btbossman]

I agree it’s definitely the kick down. I haven’t used it at all, but accidentally did for the first time last night and the torque is notably mote instant and violent, especially with my tune. Manual mode only from now on.

[Proctor750]

I would love to know the per unit cost savings to BMW as a result of switching from the tried and true keyed single piece hubs....and the guy who authorized it.
What if his hub spun? Was the promotion worth it?

[F87source]

Originally Posted by cheveux

Retorque the crank bolt?? i thought the bolt was one use/one time torque only and could not be retorqued if not new!

If that's the case then that's my mistake, in the CBC threads I keep hearing the crank bolt was retorqued before install. I may have been mistakened and the bolts holding the CBC was retorqued, I am not sure and must check again.

[Dav3]

Originally Posted by F87source

Yeah I would avoid it, you can buy a kick down blocker that prevents the pedal from entering the kick down range. This way you can slam the throttle into WOT position without worry.

But isn't the kickdown an integral part of the cars experience?

I rarely do it but its the cars best feature that allows you to truthfully express and experience the real potential of the engine

DCT is objectively a more sterile experience than MT. Flappy pads suck. Kickdown (that last accelerator pedal bit after the notch) is the only thing a DCT is better at than the Manual when trying to create explosive power and acceleration.

Like you can't expect people not to use kickdown. I've done it on every BMW I've owned and/or driven. If you've never done it, please try it, you don't need a 600hp tune to feel fast, just do kickdowns until warranty expires

[F87source]

Originally Posted by Dav3

But isn't the kickdown an integral part of the cars experience?

I rarely do it but its the cars best feature that allows you to truthfully express and experience the real potential of the engine

DCT is objectively a more sterile experience than MT. Flappy pads suck. Kickdown (that last accelerator pedal bit after the notch) is the only thing a DCT is better at than the Manual when trying to create explosive power and acceleration.

Like you can't expect people not to use kickdown. I've done it on every BMW I've owned and/or driven. If you've never done it, please try it, you don't need a 600hp tune to feel fast, just do kickdowns until warranty expires

I don't think it's an integral part of the experience, it just feels like the car is doing something on it's own which I hate, I want to be in control of the driving experience, so thats why I feel the kick down is annoying.

However that being said I do understand why it is so much fun, but it has been linked to the crank hub slipping since it's so aggressive in how in dumps multiple gears instantly.

Overall there isn't really anything you can do about it, the kick down causes issues with the crank hub and it's really a gamble Everytime you use it. Whether or not it causes issues overtime remains to be seen, so if you don't plan on keeping it after the warranty then just go wild. Or if you have the n55 m2 you should be ok, since I've yet to hear this occur on the n55 or n54 motors with the auto or dct kick down.

[mikeyymonster]

Forgive my ignorance as I've been driving stick my whole life, but is a kickdown essentially "flooring" it when you are in a high gear? I was considering DCT for my next car, but this has me second guessing that decision. So as long as you are only flooring it from a stopped position, then this can be avoided? What happens if you want to pass someone aggressively on the highway?

[pz619]

Originally Posted by mikeyymonster

Forgive my ignorance as I've been driving stick my whole life, but is a kickdown essentially "flooring" it when you are in a high gear? I was considering DCT for my next car, but this has me second guessing that decision. So as long as you are only flooring it from a stopped position, then this can be avoided? What happens if you want to pass someone aggressively on the highway?

Kickdown is essentially flooring it, at the same time the transmission will select the lowest gear possible to give you maximum power. I don't have a DCT but understand it drops gears very fast and violently.

From a 6MT standpoint it's like driving in 6th gear at 55 mph, then dropping the transmission/clutch to 2nd gear with the pedal on the floor. Most of us don't drive like that, so it's generally not an issue for us 6MT people.

[Big Fabri]

Originally Posted by mikeyymonster

Forgive my ignorance as I've been driving stick my whole life, but is a kickdown essentially "flooring" it when you are in a high gear? I was considering DCT for my next car, but this has me second guessing that decision. So as long as you are only flooring it from a stopped position, then this can be avoided? What happens if you want to pass someone aggressively on the highway?

nope.
the kickdown is a system you activate with a button. the button is in the final mm of the accelerator pedal. if you try, with the car switched off, you will feel a king of resistance at a certain point.if you press with more force you will feel this botton or switch. when pressed it send and imput to the engine telling that you require the maximum acceleration. to achive this acceleracione the engine whille adding boost downshift as much as possible. it could be even 4 gears. not try to immagine the stress you put on the drivetrain by using it. Ferray, lambos and so on does not have the switch because of this.

[Big Fabri]

here is a video that explains it better than 1000 words

[doughboy]

I never use it out of mechanical sympathy.

Just drop the gears manually prior to accelerating, just like you would in a manual.

It's quicker this way for overtaking as you are in the gear you want BEFORE you gas it rather than waiting for kickdown AFTER you press the gas.

...and its kinder on the car..

[ChrisK]

Originally Posted by doughboy

I never use it out of mechanical sympathy.

Just drop the gears manually prior to accelerating, just like you would in a manual.

It's quicker this way for overtaking as you are in the gear you want BEFORE you gas it rather than waiting for kickdown AFTER you press the gas.

...and its kinder on the car..

Totally agree with you.