Crank Hub Issue Master Thread: What You Need To Know!

[CaryTheLabelGuy]

Originally Posted by Boss330

Not that it matters, but you actually where the third person to mention this in the original "spun sprocket thread"...

Just for the record; I mentioned it first on September 28th, then hotrod2448 mentioned it on October 4th, and then you quoted him the same day and basically repeated what he had said...

One of your first replies in that thread was that even the std S55 had enough torque to mandate a keyed sprocket, later changing that view to "engine torque doesn't matter".

I notice that you also claim to have said, in private, for a long time that hard downshifts on the DCT probably is the causal factor. Wish you had shared that knowledge with the rest of us at an earlier stage. I think we all would have appreciated being pointed in that direction. I didn't personally think of that scenario until some other member questioned if hard shifts could be a problem. I have not seen anyone else (besides me) here discuss this previously either. If you only had shared your thoughts earlier, you could have taken the public credit as well (which seems to have been the point of your post)

I'll go back and look at the thread again and report back.

In the mean-time, I didn't have as much data back when I originally speculated on the DCT being a possible cause of this crank hub failure, it was just pure speculation as I was trying to understand what was causing this issue. I, unlike some people, try not to just throw everything that goes through my head out into the Internet. I have been perplexed by this situation and have gone back and forth, like many of us, on what was causing this, how widespread the issue is and how to fix it.

Edit: it appears you did speculate on the possibility of engine torque having nothing to do with this issue just before I did. However, I never saw your post previously to this. Further clarification on my point in that thread was that the S55 was considered a high-performance engine (high torque/power) that will be beat on and was designed to be raced and this warranted a keyed crank hub for this reason and that less high-performance engines (less torque/power) featured keyed crank hubs. I was, at no time, meaning that this issue had anything to do with torque/power levels themselves.

Also keep in mind, we didn't have nearly the info that we now have on this topic. There has been a lot of back-and-forth from all of the knowledgable posters on this topic, including yourself.

[04RC51]

Originally Posted by CAOZKAN

They pm'ed me and they gave me two options which are very fair to be honest. I still think of them as the good guys who made a mistake along the way of developing new stuff for this platform.
However, now the confusing part is that should I wait for a new/better part or should I give up on the crank hub. I won't be using too much tuning on my car till the warranty is over, still I can't decide given the fact that this is also happening even to stock cars.

Brand new cars have had rear diffs fail too. Stuff breaks bro!

[JcLusso]

Originally Posted by CaryTheLabelGuy

I'll go back and look at the thread again and report back.

In the mean-time, I didn't have as much data back when I originally speculated on the DCT being a possible cause of this crank hub failure, it was just pure speculation as I was trying to understand what was causing this issue. I, unlike some people, try not to just throw everything that goes through my head out into the Internet. I have been perplexed by this situation and have gone back and forth, like many of us, on what was causing this, how widespread the issue is and how to fix it.

CaryTheLabelGuy I throw things I come up with as questions for others to answer or call me stupid! And every time I see your username I can't help but laugh!

Originally Posted by JcLusso

From what we know it appears a lot of the cars with this issue are DCT. This is either because there are a lot more DCT than 6MT (perfectly valid) or maybe something in the DCT is just very different. Also when I say a lot we still don't have a lot of data we are working with so the percentages could be completely flawed as well.

When you slam gears does it put any more stress on this part? Is it possible that the DCT shifts much harder than a 6MT?

Originally Posted by Boss330

That's a very interesting observation

When the DCT "slams" the gears (shifting up), the rpm of the crank drops in rpm accordingly as the crank rpm has to match the rpm of the input shaft in the transmission. The harder the shift, the more rapid this rpm change is on the crank. The same effect, only opposite, takes place during hard downshifts. The crank rpm must rise rapidly to match the rpm of the input shaft on the transmission.

Both of these situations cause a very abrupt shift in rpm. The rpm "jumps" from one rpm to a higher/lower allmost instantaneously. Much quicker than the engine is able to change rpm on it's own.

Since the DCT settings probably are even more aggressive on the F8x, this could potentially be the causation factor behind slip, and why the N54 and N55 (using the same sprocket/hub parts, but on much "milder" transmissions) haven't experienced the same slip problems?

Did someone also state that their sprocket had slipped the same way as crank rotation? If so, that could also be evidence supporting the slip being related to hard shifts and the following abrupt change in crank rpm.

Say the upshift is at redline in the hardest shift setting, the crank rpm drops by a few thousand RPMs in the matter of milliseconds (what is the shift time for the DCT? 8ms or 80ms). Could this rather brutal drop in rpm actually cause the sprocket to slip on the hub, as the inertia of the timing chain, camshafts etc, tries to resist that sudden drop in rpm? If so, that would explain a sprocket slipping in the SAME direction as the crank rotates...

I have never thought about this scenario until now, so I should expect someone explaing why this isn't possible

But at least, I've had a thought process and either learned something new, or just made a fool of myself...

[Irishace]

If the dct is the culprit why have we not seen this issue on the E92 M3? Are they using the same crank hub assembly in the E92 and the F80/2?

[JcLusso]

Originally Posted by Irishace

If the dct is the culprit why have we not seen this issue on the E92 M3? Are they using the same crank hub assembly in the E92 and the F80/2?

I'm guessing the DCT isn't the same.... It's also a different motor all together where as the S55 is based off the N54/N55.

[GrussGott]

Originally Posted by JcLusso

I'm guessing the DCT isn't the same.... It's also a different motor all together where as the S55 is based off the N54/N55.

Well if it's a problem then I'm just lucky I guess because I've had mine for 17 months and I hard kick-down DCT shift that bitch all the fucking time. But I'll update the thread if she blows.

[SpeedyJ]

How do I hard kickdown the car lol?

[Mandi90TT]

Originally Posted by Irishace

If the dct is the culprit why have we not seen this issue on the E92 M3? Are they using the same crank hub assembly in the E92 and the F80/2?

Well, it's also a function of engine torque and we all know about the E92 and torque, or lack thereof. ..

[jwzimm]

Originally Posted by Irishace

If the dct is the culprit why have we not seen this issue on the E92 M3? Are they using the same crank hub assembly in the E92 and the F80/2?

It looks like the timing chain gears on the S65 are integral to the crankshaft. That would make a slip impossible.

http://www.realoem.com/bmw/enUS/show...diagId=11_4118

https://www.ecstuning.com/b-genuine-...b/11210443639/

[kitesurfer]

If I had a DCT I would stick a furniture pad by the kick down button to prevent the gas pedal from activating it , I did this on a old 335i I had cause I despised that feature.

[M4toM3]

Originally Posted by Boss330

So far the knowledge we have points to DCT kickdown/WOT shifts being part of the picture.

It's still early days, but if this trend can be confirmed for the other DCT cars, I think that my thoughts on hard DCT shifting and resultant abrupt change in crank rpm becomes even more relevant. This should be considered as a possible causal factor.

For the record, when my car had it's failure, I was doing a data log, 2nd gear to 4th gear run, shifting (DCT) around 6300 rpm ish. Cars Mods: JB4, Map 8, running meth additive of 30. E85 mixed (3 gallons). After shifting into 4th I let off throttle and received and engine malfunction, game over. I only recently learned that if I down shift the car (example 7th), grab the left paddle and hold it while flooring it and hitting the kick-down, car will drop down to the lowest acceptable gear(Manual shifting mode). I never did this while tuned. I would click down my downshifts.

[Vectors2final]

Originally Posted by GrussGott

Well if it's a problem then I'm just lucky I guess because I've had mine for 17 months and I hard kick-down DCT shift that bitch all the fucking time. But I'll update the thread if she blows.

I've used it stock, and tuned.

I've been JB4/DPs for a few thousand miles now, and she runs pretty strong.

[JoeFromPA]

Originally Posted by GrussGott

porn, huh? Lucky duck.

Hehehe, pharma R&D.

[sA x sKy]

Originally Posted by JoeFromPA

Hehehe, pharma R&D.

Fellow pharmacist

[dmk08]

Originally Posted by SpeedyJ

How do I hard kickdown the car lol?

On a DCT floor it and hit downshit paddle.

[Powaup]

Great thread

[shivaswrath]

Originally Posted by Dave 90TT

Well, it's also a function of engine torque and we all know about the E92 and torque, or lack thereof. ..

Wouldn't the M5 guys be seeing this a bit then, if it was a function of torque and the DCT?

[dmk08]

Originally Posted by shivaswrath

Wouldn't the M5 guys be seeing this a bit then, if it was a function of torque and the DCT?

They are saying its a result of the torque and the DCTs fast shifts on the engine not anything to do with the DCT itself. At least thats how I read it.

I personally don't know enough about the S63 to say how it's crank hub design is but it may not be comparable at all.

[jwzimm]

Originally Posted by dmk08

They are saying its a result of the torque and the DCTs fast shifts on the engine not anything to do with the DCT itself. At least thats how I read it.

I personally don't know enough about the S63 to say how it's crank hub design is but it may not be comparable at all.

As I said previously, the S65 (and by similarity the S85) seem to have the timing gears machined out of the crank snout itself making a spin impossible.

Here is a graphic of the S85's crank showing the gears as integral to the crank:

http://www.realoem.com/bmw/enUS/show...diagId=11_3692

Originally Posted by jwzimm

It looks like the timing chain gears on the S65 are integral to the crankshaft. That would make a slip impossible.

http://www.realoem.com/bmw/enUS/show...diagId=11_4118

https://www.ecstuning.com/b-genuine-...b/11210443639/

The S63 in the F10 M5 uses a woodruff key to lock in the timing sprocket to the crankshaft (see item 3).
http://www.realoem.com/bmw/enUS/show...diagId=11_5029

[Mandi90TT]

Originally Posted by shivaswrath

Wouldn't the M5 guys be seeing this a bit then, if it was a function of torque and the DCT?

I was being facetious, and poking fun at the E92 crowd. The little wink eye smiley at the end was the tip-off. Sorry if my humor/sarcasm wasn't clearer.

[CaryTheLabelGuy]

Originally Posted by jwzimm

As I said previously, the S65 (and by similarity the S85) seem to have the timing gears machined out of the crank snout itself making a spin impossible.

Here is a graphic of the S85's crank showing the gears as integral to the crank:

http://www.realoem.com/bmw/enUS/show...diagId=11_3692




The S63 in the F10 M5 uses a woodruff key to lock in the timing sprocket to the crankshaft (see item 3).
http://www.realoem.com/bmw/enUS/show...diagId=11_5029

Exactly. As far as I know, this version of DCT isn't in any other car other than the F8x that uses the same non-keyed crank hub assembly.

[smithf80]

Dackelone how do you feel about a sticky on this? Seems like some good important discussion going on here.