[JcLusso]

TL;DR:
1. DO NOT replace the OEM Crank Hub with the TPG Tuning Crank Hub!
2. If you have installed it already you now have a ticking time bomb. If it
fails it will fail in a worse way than the OEM crank hub potentially causing
more damage to your motor.
3. Possibly speculations lead to the heavy use of the kick down being a possible
cause of the crank hub spinning. This is just a speculation!
4. The same part has been used on high power N54 and N55 motors with out this
problem. (adds to the speculation behind the DCT maybe causing this)

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Poll (answer it!): https://f80.bimmerpost.com/forums/sh...php?p=24053449

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Overview:
The point of this thread is to bring proper awareness in regards to
the S55 crank hub and TPG Tuning. There are currently many threads with lots of
information, but the issue is the important and relevant information is buried
within hundreds of posts. Unfortunately, TPG Tuning created this
entire mess when they started pushing out the word that you should replace this
part to prevent catastrophic engine failure.

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What you need to know about TPG Tuning and their crank hub
Back in August of 2015, TPG Tuning came out with this large post claiming how they
found the weakest point in the S55, the spinning crank hub. They claimed that
this issue exists in stock cars, but is more prevalent in cars with increased
power. Being a vendor on the forum one would assume this company knows what
they are saying and has done the necessary research and development to back
this all up.

Well that's where things go wrong. Let's start by going through all the reasons
you should not trust TPG Tuning.

Lets start by picking apart TPG's original statement seen here

Originally Posted by TPG Tuning

Hello Bimmerpost!
The S55 , like many other BMW Engines, does not have a woodruff key locating
the crank timing gear. The life or death of your engine is 100% determined by
ONE bolt pressing the timing gear against the crank. With the incredible
amount of Horsepower and Torque these engines are capable of, even with simple
bolt on's , it quickly overcomes the pressure applied by this bolt.
When this happens the timing gear spins on the crank, throwing your engine out
of time. If this occurs , more often then not it will result in catastrophic
engine failure.

In this original post from TPG Tuning they make a few bold claims.

Catastrophic Engine Failure
This was simply a marketing scare tactic TPG created to help drive sales for their
overpriced OEM hub that they made minor modifications to. Of the failed crank
hubs (low reports) there are no reports AFAIK of the engine being catastrophically
damaged.

The chance of your engine being damaged is actually far more likely with the
TPG crank hub as explained below:

Originally Posted by Boss330

In fact, the end result of a slipped TPG sprocket causes more damage than a slipped stock sprocket.

On most slipped stock sprockets we have heard about, the problems usually was a "drivetrain failure" warning, rough idle or worst case, engine not running. That's because the sprocket only slipped partially, or a couple of degrees. Enough to put the cam timing out and cause the error codes and rough idle.

On the TPG slipped sprocket, the sprocket has split in half, hub and key has been damaged (beyond repair). Also most likely damaging the timing chain as the sprocket splits. Whats worse is that since the sprocket breaks/splits, it becomes completely loose on the hub. The crank now rotates with zero drive transferred to the timing chain and cams... As explained previously by the guy experiencing the TPG failures, the engine could not run when the TPG parts failed, since there was no drive to the camshafts anymore (while the engine still keeps running on several cars that has the std sprocket slip).

In fact, it's much more likely that a slipped TPG sprocket can lead to catastrophic engine failure than the std part, since the std part seems to just slip a few degrees while the TPG sprocket splits in half and rotates freely on the hub... Fortunately, no catastrophic engine damage was experienced even in that scenario. Which also makes it even more unlikely to occur with the stock parts (since degree of slip seems to be small enough that the engine usually runs even after the slip has occurred).

It Will Stop The Crank Hub From Spinning
TPG originally claimed this was the purpose, but after heavy criticism they
changed their statements to it being solely to help position the crank hub during
installation. There are many issues with these statements.

Originally Posted by TPG Tuning

If the assembly is installed and torqued properly there should be no more stress or load on the gear then there previously was . Therefore having the gear located and pinned would do its job easily without providing anymore stress to the gear. The design in any instance is not to continually apply force to the pin or gear in hopes it retains its location. The idea is to locate the pin and timing appropriately and lock it in while being torqued to prevent further movement.

1. They changed the reasoning behind the part months after when questioned
2. Now they've changed the design of this part to be solely to help position
during installation. In my opinion this inherently is suggesting BMW has
an assembly problem which basically renders this part useless.

When TPG was questioned about all these inconsistencies they stopped responding.

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Research & Development
TPG has none of this. All of their research is based on a small sample set.
For some reason they concluded this was an issue with barely any information.
They also have very little knowledge or understanding of how to develop
a part of this complexity. People with far more knowledge were able to push
them over the edge and leave them answerless to many technical questions.

Also the design is like no other. They decided to make a half circle groove with
a pin instead of a square peg. Their reasoning was to remove less material.
Unfortunately, they still were unable to answer any questions in regards
to properly testing this part besides installing it in their own cars.

TPG showing they don't have a clue what they are doing


Great analogy for why this part makes no sense...

Originally Posted by hotrod2448

The real question is why do people seem to think this component would see any/significantly more load in a 700hp or 1000 lb/ft application than stock? The load on this component is a function of the power required for the crank to run the valve train which should not change with increases in power, unless you are increasing maximum RPM, valve springs or cam profiles.

This is like saying a tuned car is much more likely to slip the alternator belt than a stock car.

Part has a long history...

Originally Posted by Boss330

The sprocket (hub or whatever it's called) is the same item/part number as used since April 2001 on numerous BMW engines and cars:

http://www.realoem.com/bmw/enUS/partxref?q=11317502180

This seems to be a proven concept and part, albeit in lower HP level engines. But AFAIK highly tuned N54 and N55 engines still rely on the stock sprocket?

As mentioned previously, my main concerns regarding the TPG solution is down to what I consider a flawed analysis of what the root cause of the issue is and a poor execution of how to fix the alleged problem. This is just a "internet analysis" on my part though, only having the pictures and information provided here by TPG and other members as a basis of my concerns.

sA x sKy aka Sameet's failed TPG crank hub




The OEM gear showing stress marks in it. This should've been a huge red flag
when TPG considered cutting a notch into this part a reasonable way to fix
the problem.



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Intentional Built-In Fuse?
There is speculation that BMW intentionally did not key the crank hub because they essentially designed it as a fuse so if you money-shift the car you're less likely to destroy the motor.

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Easier to Assemble:
There is speculation that the reason the crank hub is not keyed is because it makes assembly much simpler.

Originally Posted by Boss330

Automated manufacturing and assembly is easier without a woodruff key. The manufacturing of the hub and sprocket is simpler because there is no need to align the teeth on the sprockets with a groove for the key. The hub/crank snout can be mounted without the need to be in a particular position. During assembly the crank is correctly positioned relative to the cams. Then the robots can place the timing chain, sprocket and hub straight on the crank. no need to position a woodruff key before putting the hub and sprocket in position. Mounting of the sprocket on the hub is also much easier, in an automated process, without a woodruff key.

The design, IMO, is purely there because of assembly requirements. Not because it's a "better" design for strength...

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DCT Speculation / Aggressive Shifts:
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. When you look into how
the DCT shifts it does it much faster than any human could. In the most
aggressive state it will shift at 8ms.

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...

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List of failed crank hub cars
This is a list of all of the cars that I have been able to collect regarding
failed crank hubs. Note that two or more of the cars were built in late 2014.
If you can provide any more information to this list please comment and I will
add it.

BrokenM4
Build: 11/14
OEM Failure: YES
Mods: JB4, Map 8, running meth additive of 30. E85 mixed (3 gallons)
Transmission: DCT
Notes: Failed during data log 2nd-4th gear run w/ 6300RPM shifts

sA x sKy aka Sameet
Build: 11/14
OEM Failure: YES @ 13k miles
TPG Failure: YES (3 total) @ 13k, 17k & 17k miles
Mods: Upgraded Turbos, etc
Transmission: DCT
Notes: Failed during use of kick down

BarronM
Build: def after 11/14
OEM Failure: YES and replaced with OEM
Mods: ?
Transmission: ?

BlueBYyouM4
Build: late 2014
OEM Failure: YES
Mods: FBO + Meth
Transmission: DCT

Blipit
Build: ?
OEM Failure: YES
Mods: ?
Transmission: ?

chrisjguzman
Build: ?
OEM Failure: YES
Mods: ?
Transmission: ?

Pennzoil
Build: 8/14 RHD
OEM Failure: 1/3 tooth spun
TPG Failure: NO
Mods: FBO + JB4 + 50:50 meth , using oct93 (ron98) pump gas only
Transmission: DCT

Undisclosed Name
Build: around 8/2015
OEM Failure: YES
Mods: Upgraded Turbos, etc
Transmission: DCT
Notes: Failed during use of kick down

Undisclosed Name
Build: before 11/14
OEM Failure: NO
TPG Failure: YES
Mods: Upgraded Turbos, etc
Transmission: 6MT

Undisclosed Name
Build: 11/14
OEM Failure: NO
TPG Failure: YES
Mods: FBO + Tune (ESS Estronic)
Transmission: DCT
Notes: Failure caused catastrophic engine damage. Valves were bent etc.

M4 CSL
Build: 10/14
OEM Failure: YES
Mods: FBO
Transmission: DCT

Total OEM Failures: 8
Total TPG Failures: 5
Builds w/ Similar Production Dates: 8

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Jason from TPG spewing off bullshit with all his fan boys / employees
trying to back him up. Just shows further how half the people that
make the claims are all on the TPG side.



Anything in regards to the crank hub problem itself is simply speculation.
There is no confirmation on if this problem exists or does not or what causes it.
This post is simply a place to combine all the thoughts regarding this issue.

I also want to thank all the members of the forum that put in a lot of input
in the related crank hub threads. Thanks to Kr3st for bringing
the topic back into the light. Thanks to Boss330 for writing
some amazingly detailed posts with some very valuable information. Thanks to
sA x sKy for providing some good photos. Thanks to
Powaup for starting the very useful poll

If anyone thinks i've missed valuable information please let me know and I'd be happy to add it.

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Sources:
TPG Tuning S55 Crank Hub
Official Thread: Report Here if you Spun your Crank Timing Gear Hub.
Crank hub fix? You decide.
Poll: Crank Hub issues