[stefan]

This is hilarious. If you were to send your torque spec to the moon with a piggyback why wouldn't you install at least a crank hub capture plate? It makes no sense to me. This whole kickdown thing is irrelevant as well. This is a torque issue. BMW for whatever reason used a part here that, in the best of scenarios, handles the stock torque and that's about it.

Kudos on not trying to weasel into a warranty situation. Btw I suspect since your timing was so off that it had slipped slightly in the past and your startup just was the FNITC.

One more thing. To those saying "well that's weird I live in (sea level country) and I've never seen a spun crank hub", consider that, at altitude, these motors run a nontrivial amount of increased boost to compensate. Could be why you hear about it more in some places versus others.

Anyway enjoy your new build! As far as M motors go, the fact there is only one relatively simple failure point is a blessing. No water pump or rod bearings on the s55

edit: I have rethought this, and the capture plate makes no sense. Doesn't change the sprockets from spinning and unequal rates. That's what affects timing and can lead to failure. I have also concluded that one way or another the crank hub setup on these cars is just bad. It "should be fine" but why it isn't keyed is beyond weird.

[Ratcher]

Originally Posted by F87source

1) IIRC this was from a money shift so it's not a case of the bolt getting loose.

2) The way the metal is sheared around the bolt holes it looks like the hub spun counter clock wise while the crank bolt did not move causing the sheering. So they were lucky the crank bolt capture did not loosen the crank bolt because the metal sheared before hand.


This is my prime concern with these bolt captures, because if the crank hub spun counter clock wise, and the bolt capture is strong enough to do its job, it will losen the crank bolt and make the entire scenario even worse than if it was not present.

You may be right, I dont know all details and I got this picture looong ago, but iifc it was from an M2C with a lot of power, something like 700-800hp, which makes me question it being a manuel. Nevertheless even if a money shift, it spun; with the one-piece crankhub fix it wouldnt have spun.

Every good shop I know nowadays recommends people to avoid this capture plate and go straight to the one piece crankhub solution

[Robin_NL]

Originally Posted by Ratcher

You may be right, I dont know all details and I got this picture looong ago, but iifc it was from an M2C with a lot of power, something like 700-800hp, which makes me question it being a manuel. Nevertheless even if a money shift, it spun; with the one-piece crankhub fix it wouldnt have spun.

Every good shop I know nowadays recommends people to avoid this capture plate and go straight to the one piece crankhub solution

Cheers
Robin

[beezyM2C]

Originally Posted by stefan

This is hilarious. If you were to send your torque spec to the moon with a piggyback why wouldn't you install at least a crank hub capture plate? It makes no sense to me. This whole kickdown thing is irrelevant as well. This is a torque issue. BMW for whatever reason used a part here that, in the best of scenarios, handles the stock torque and that's about it.

Kudos on not trying to weasel into a warranty situation. Btw I suspect since your timing was so off that it had slipped slightly in the past and your startup just was the FNITC.

One more thing. To those saying "well that's weird I live in (sea level country) and I've never seen a spun crank hub", consider that, at altitude, these motors run a nontrivial amount of increased boost to compensate. Could be why you hear about it more in some places versus others.

Anyway enjoy your new build! As far as M motors go, the fact there is only one relatively simple failure point is a blessing. No water pump or rod bearings on the s55

edit: I have rethought this, and the capture plate makes no sense. Doesn't change the sprockets from spinning and unequal rates. That's what affects timing and can lead to failure. I have also concluded that one way or another the crank hub setup on these cars is just bad. It "should be fine" but why it isn't keyed is beyond weird.

crazy how long it took someone to come post the right answer..its trq 100% there is a reason why all of the OTS maps are trq limitied to 553. Rods dont like more than 680-700wtrq DCT trans doesn't and MT likes even less. pretty much every component known to fail on the s55 does so because of trq
CBC does nothing after the fact of get the hub properly done

[doughboy]

Respectfully you guys are not thinking what torque is and how its equally about torque reaction as about torque action..

Think about it. If you have a 1000lbft engine, if it is turning a small load (say a water pump) with a max torque reaction of 25lbft then the max torque that the 1000lbft motor can ever apply to the water pump is 25lbft.

The torque reaction from the s55 valve train is constant over rev range and pretty small, regardless of how much torque the engine can put out at max load. The maximum torque possible (thus acceleration) to the valve train is either free revving in neutral or during aggressive kickdown or bad MT downshift, neither of which are related to tuned max load torque output. The engine could never apply its max torque to the valve train.

The torque reaction from the gearbox is overwhelmingly more than the valve train so the tuned engine torque will only ever over load transmission etc, the valve train will not be affected during driving by crank torque. Only overaccelerating or over revving the valve train will result in higher torque values that may causd CH spin and this can be done with any standard engine easily if driven badly enough.

[Twonice2485]

Originally Posted by SpecialEdition_F87

To everyone's point yes, I was tuned and modified. Roughly was only 530whp and 560wtq during its time. So about 580hp 600tq to the flywheel. I'm here to provide data.

I hope we can take something away from this.

1. I have never once used kickdown in the vehicle and there's many posts about people arguing kickdown causes the spin. (debunked)
Can it accelerate it? Maybe?? But this spin should put all that kickdown to rest. You'll still spin it if your tuned

2. I have never launched the car, I have never tracked the car. However yes I do accelerate and race the car on a closed course. 90% of the cars life is spent commuting to work. The other 10% is spent enjoying the car and ripping on it

3. 2021 s55 have done nothing to adress the fix and I'm unsure if that's been verified yet. I know 2020 have been verified to no crankhub update. This spin should set in stone 2021 hasn't either.

4. I have never taken the car past 7,000 rpm in the past 10,000 of it's 14,000 mile life. Mainly cus it just falls flat. Take this data how you wish….

Lemme end with this, If you are tuned you are simply playing with fire. And just because your car hasn't seen a spun crankhub doesn't mean it hasn't already slipped and knocked camshaft timing off slightly but still within tolerance. The further it slips out the worse it gets.


After breaking down the motor we seen signs of the camshaft timing slowly moving further and further over the course of a few months. This could be happening to your s55 as we speak. And you won't even know it. I didn't. So be careful and get it done. Living life on a wish and a prayer isn't worth it. Suck it up pay the 1,800-2,200 and move on. If you are stock don't worry about it. To the tuned hopefuls it's a matter of time. Regardless I'll put money on the fact that your car has already begun to slip. You might get lucky and it never will fully spin but with this motor it'll start slipping and you will have zero clue.

Is this on 93oct, what are you running on full E if you're tuned for it?

[Tech567]

I've seen them spin bone stock. It's that flimsy friction disc BMW puts between the sprockets to keep them from jumping time. That why solid one piece hubs are the best in my opinion.

[Suds]

I’m reading this and thinking it’s a crap shoot.
I had a 2015 M4 6mt that I tracked for over 3,500 miles on BPM stage 1.
I have a 2019 M4 DCT that I have tracked over 3,500 miles BM3 stage 1. 24k miles on the car.
I have a 2019 M2c DCT that has over to 6,000 track miles on it BM3 stage 1 and stage 2 E85. 14k miles on the car.
The S55 is damn reliable.

[chris719]

Originally Posted by Suds

I’m reading this and thinking it’s a crap shoot.
I had a 2015 M4 6mt that I tracked for over 3,500 miles on BPM stage 1.
I have a 2019 M4 DCT that I have tracked over 3,500 miles BM3 stage 1. 24k miles on the car.
I have a 2019 M2c DCT that has over to 6,000 track miles on it BM3 stage 1 and stage 2 E85. 14k miles on the car.
The S55 is damn reliable.

Appreciate the data point, but small sample size and somewhat low miles, although a lot on track for sure. I don't think you can really establish reliability without a large dataset.

[JoanLluch]

Originally Posted by Suds

I’m reading this and thinking it’s a crap shoot.
I had a 2015 M4 6mt that I tracked for over 3,500 miles on BPM stage 1.
I have a 2019 M4 DCT that I have tracked over 3,500 miles BM3 stage 1. 24k miles on the car.
I have a 2019 M2c DCT that has over to 6,000 track miles on it BM3 stage 1 and stage 2 E85. 14k miles on the car.
The S55 is damn reliable.

I think one of the points that are made here is that it does not really matter whether you track the car or what tune do you applied to it. My conclusion after reading this and other threads on the subject is that crankhub spin happens more with M6T cars and it is ultimately caused after cycles of wild forward-backward torque applied to the transmission. By backward torque I mean bad/quick downshifts with no rev-matching, which may instantly subject the crankhub to far more torque that the one available on the engine, regardless of tune.

So if that's the case, it ultimately looks that it may depend on the driving style whether this will happen or not.

[chris719]

Originally Posted by JoanLluch

I think one of the points that are made here is that it does not really matter whether you track the car or what tune do you applied to it. My conclusion after reading this and other threads on the subject is that crankhub spin happens more with M6T cars and it is ultimately caused after cycles of wild forward-backward torque applied to the transmission. By backward torque I mean bad/quick downshifts with no rev-matching, which may instantly subject the crankhub to far more torque that the one available on the engine, regardless of tune.

So if that's the case, it ultimately looks that it may depend on the driving style whether this will happen or not.

This may be true for stock cars, but many tuners have spun when pushing big numbers. It’s definitely happening more frequently in Stage 2+ cars.

[JoanLluch]

Originally Posted by chris719

This may be true for stock cars, but many tuners have spun when pushing big numbers. It’s definitely happening more frequently in Stage 2+ cars.

My point also was that people willing to install a Stage 2 tune in their cars, might be a lot more prone to push hard the car in tracks or street races compared with regular users. Some of them might not be fully professional drivers so they might actually 'abuse' the car transmission in wrong ways that might ultimately cause the crank thing to fail.

I mean I believe that the same kind of 'abuse' on a stock car might actually cause exactly the same issues because that's when excessive torque -beyond the linear one produced by a Stage 2- is actually supported by the transmission

[chris719]

Originally Posted by JoanLluch

My point also was that people willing to install a Stage 2 tune in their cars, might be a lot more prone to push hard the car in tracks or street races compared with regular users. Some of them might not be fully professional drivers so they might actually 'abuse' the car transmission in wrong ways that might ultimately cause the crank thing to fail.

I mean I believe that the same kind of 'abuse' on a stock car might actually cause exactly the same issues because that's when excessive torque -beyond the linear one produced by a Stage 2- is actually supported by the transmission

Maybe. I asked an instructor at M School about this and he said they had very few issues, and those cars are beat on by both good drivers and bad. They are all stock, though.

[ftw]

Capture plate is only there to stop the crank bolt coming loose.