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

[jwzimm]

Originally Posted by Boss330

Indeed it is at the rear end of the crank...

Under high rotational force situations a crank can twist from front to rear. On Top Fuel engines, this twist can be so many degrees that the camshaft lobes are actually offset from front to rear, to achieve a relatively correct valve timing under max power...

It's not anywhere near that on a production engine, but with the sprocket close to the clutch, cam timing isn't affected by torsional twist of the crankshaft from flywheel to front end. On engines like the N55/S55, there could possibly be some twisting of the crank between the flywheel side to the timing chain sprocket side, in situation like a hard clutch dump or hard shift. Dump the clutch and the flywheel side "stops", while the pistons forces the crank to rotate, and applies a massive force on the crank. The farther away you get from the flywheel (like cyl 1 and 2) the more likely this force applied on the crank leads to a twist on the crank. In these scenarios, the timing chain, driven from the sprocket at the front of the crank, could actually be a few degrees "ahead" of the flywheel side of the crank. And thus, throwing the valve timing off.

Placing the sprocket and valve timing on the flywheel side means that there isn't any twist between flywheel and cam timing...

If this is has anything to do with why they went for this design I have no clue about. I don't know, here and now, if crank twisting is any real issue on a high performance street engine...

Very interesting but I sincerely doubt that it is an issue in these engines. The crank is very stout and the degree to which it will twist is likely on the order of thousandths of an inch or less. The quote you cited in your first statement is referring to camshaft twist which, in Top Fuel Dragster engines can be an issue due to their long cams combined with the ridiculous levels of acceleration that these engines produce.

If I were to guess I would say that BMW made this design change for production purposes and not in service performance issues.

[JoeFromPA]

I had forgotten the S55 was built alongside the N55. That being said, the crank hub is a seperate part and I would anticipate a woodruff key crank hub would be no big deal to make for the S55 if it was determined to be necessary as compared to the N55 due to transmission or other differences.

That being said, that's a really valid reason that BMW would have an inherent interest in keeping the S55 similar to the N55 as much as possible. Which still raises the question: Why is the N55 non integral and non-keyed?

[sA x sKy]

Originally Posted by Boss330

Also interesting to note that the new mdoular engines, including the B58 (new 3l I6 engine) has a sprocket that is integral to the crank, just like on the S65, S85 engines. No slipped sprocket issues on these new engines then...


http://www.realoem.com/bmw/enUS/show...diagId=11_6364

B58 and B48 crankshafts below:

Damn... fuck BMW.

[jwzimm]

Originally Posted by JoeFromPA

I had forgotten the S55 was built alongside the N55. That being said, the crank hub is a seperate part and I would anticipate a woodruff key crank hub would be no big deal to make for the S55 if it was determined to be necessary as compared to the N55 due to transmission or other differences.

That being said, that's a really valid reason that BMW would have an inherent interest in keeping the S55 similar to the N55 as much as possible. Which still raises the question: Why is the N55 non integral and non-keyed?

Boss330 already addressed that question:

Originally Posted by Boss330

snip...
The S55 is built on the regular engine plant, alongside N55 engines. No "M engine builders" are involved in the manufacturing process.

The S55 is based on the N55, to the point that:

• The sprocket is identical to what's on the N55, N52, N53, N54, N46, N43, N45
• The hub is identical to the N55 part

...snip

What we are looking at here is legacy design that has been carried over across generations. It was likely originally designed on those lower output engines and then evaluated and adopted into the newer designs. In these situations is it very possible that the increase in output has eaten up the margin originally included in the basic design such that you get some "squeeze-out" and the occasional failure.

[JoeFromPA]

Originally Posted by jwzimm

Boss330 already addressed that question:

So that didn't actually answer my question, but it does help. Let me pose it a different way though:

Why would you build a non-integral, non-keyed crank hub AT ALL. We've established keyed/integral is not tied to power output. All of the engines you named, IIRC, have pretty similar RPM ranges around 7,000 rpms. So any of them it's possible, in a MT, to go from idle to 7,000 rpms just by dropping into a gear at speed.

So why is there any crank hub design that does not use at least a woodruff key?

[Boss330]

Originally Posted by jwzimm

Very interesting but I sincerely doubt that it is an issue in these engines. The crank is very stout and the degree to which it will twist is likely on the order of thousandths of an inch or less. The quote you cited in your first statement is referring to camshaft twist which, in Top Fuel Dragster engines can be an issue due to their long cams combined with the ridiculous levels of acceleration that these engines produce.

If I were to guess I would say that BMW made this design change for production purposes and not in service performance issues.

Yeah, those Top Fuel engines can have as much as 20 degrees of twist..!!!

There is enough twist in a engine like the S55 to necessitate a crankshaft vibration damper, so some degree of twist takes place:

http://www.atiracing.com/products/dampers/101/

While your engine is running, some pistons are being pushed downward on a power stroke, some are being pulled down by the crankshaft, and some are being pushed upward by the crankshaft. Now envision this entire system happening 8,000+ times per minute! Even further, all of these different actions are happening to the same piece of metal - the crankshaft. These actions make the shaft twist in one direction away from its natural home location, and when it tries to come back to that home location, its momentum makes it travel past its original location and farther in the other direction.

The measured magnitude of that action is called “Degrees of Twist – Peak to Peak” or crankshaft twist. This is what I measure when I am damper testing. It is this action that breaks parts and robs you of horsepower when there is nothing to counteract and eliminate the twist. In this system, the worst torsional vibrations, or twist, will always occur at the farthest point from the greatest load, or the heaviest mass. A torsional twist is defined as a twist without a bend. If you get too much of this twist, you will have a bend and this will cause engine and/or crank failures. Think about twisting a piece of rope over and over; you can make one or two revolutions and nothing happens. After that it starts to get a wave in it, and then as you twist more, the rope will pull your hands closer together.

Once torsional vibrations get to the front of the engine, something there needs to counteract that motion. This is where the damper comes into play. The damper’s job is to absorb and counteract as much of the twist as possible. With the right damper on your engine, the majority of the twist can be eliminated. However, with the wrong damper, virtually all of the twist can remain. A damper’s job is to rebound like the recoil of a spring. In this case the spring is your crankshaft twisting and when it tries to rebound past that natural state we discussed earlier, that is when the damper needs to stop it.

There are some technical papers on the topic of crankshaft twisting, where valvetrain and crank synchronisation also is mentioned as a issue of crank twist.

A regular crank in a production engine does see twist of up to two degrees from front to back of the crank. The long crank on a I6 engine is more prone to twist than a shorter I4, V6 or V8 crank.

http://www.atiracing.com/products/dampers/testing/



Some articles on the subject:
http://www.wccm-eccm-ecfd2014.org/ad...ract/a1964.pdf
http://www.dragtimenews.com/dampers101.htm
http://www.ata-e.com/uploads/Whitepa...Vibrations.pdf
http://www.vntr.ru/ftpgetfile.php?id=663
http://www.ijer.in/ijer/publication/...R_2013_602.pdf
http://www.bhjdynamics.com/downloads...amper_Info.pdf

[Boss330]

Originally Posted by JoeFromPA

So that didn't actually answer my question, but it does help. Let me pose it a different way though:

Why would you build a non-integral, non-keyed crank hub AT ALL. We've established keyed/integral is not tied to power output. All of the engines you named, IIRC, have pretty similar RPM ranges around 7,000 rpms. So any of them it's possible, in a MT, to go from idle to 7,000 rpms just by dropping into a gear at speed.

So why is there any crank hub design that does not use at least a woodruff key?

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...

[jwzimm]

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...

In addition, it has been speculated that this design can function as a "money-shift" fuse. That could be an intentional design.

[AustinY 2208]

Originally Posted by sA x sKy

Maybe you should get your head out of your ass too. I said before, the TPG solution wasn't the best one.

[schnazzy]

This is an interesting read....

First I'd like to thank the OP JcLusso, for putting this together was an effort and it is appreciated. Also, TPG for responding was classy.

If JcLusso wouldn't mind taking some constructive thoughts... because of some of the extreme statements and in particular a couple conclusions like TPG asking about what materials another company used and trying to stretch that to the conclusion that TPG doesn't know anything actually reduces my believe in your other statements. If you stetched there, where else?

Also, the extreme statement just cause flame wars and if that was what you were after, ok, cool, job done but that much work, I'd assume you really wanted to help the community so having a less biased tone and coming at it with full disclosure and a mediated tone would strengthen your post.

Having said that, again, appreciate the work and the post. I'd definitely like to see more car stats.

[Boss330]

Originally Posted by jwzimm

In addition, it has been speculated that this design can function as a "money-shift" fuse. That could be an intentional design.

Agree that my wording "purely for assembly" was a bit to conclusive

However, I feel that the crank design of the new modular engines, with a machined sprocket integrated in the crank, kind of weakens the argument regarding money shifting. The new design does not allow slippage so it does not have that "function" designed into the valve drivetrain...

So it seems they do not think slippage is a necessary safe guard, at least not on the new modular engines...

[FIRSTM3NYC]

First I must say I am no mechanic.... I will just stat the facts.

I am one of the guy that bought the TPG crank hub. I even had them install it. I had no crank hub issues before hand, car was perfectly fine. I had it installed as a preventative measure as TPG indicate... To this day my car is running perfectly fine with no issues.

Car:
F80 M3 Dct

Current Mods:
TPG Hub
dps
er charge pipes
meth
jb4
pure turbo stage 2
Dodson clutch packs

I don't track the car.
it is a daily driver.
I do drive aggressive but within reason, meaning I don't redline. no burn outs. Im more of a spirited driver.
My build date is 4/15/2015.

besides the installation on the TPG Hub and clutch packs, Only one tech touched my car.

Hopefully we can resolve the crank hub issue and move forward with this platform.

Of course if my crank hub goes I will let you guys know.

#resolvethisissuetogether

[hotrod2448]

I agree that the integrated sprocket on the new motors pretty much blows the "gear is an engineered weak link" argument out of the water.

As far as the moving the timing chain to the back of the engine argument for twist goes, I don't think that's the reason. Unless you have a sensor at each end of the crank so you can actually measure deflection, one end of the block will always be very slightly off. I just swaps from cylinder 6 being out to cylinder 1 now. I would think they could (and maybe already do) use load calculations to build an offset for fuel and spark into their engine mapping anyway. Even then you aren't going alter your cam timing fast enough to do much about that. I'm guessing moving the timing chain is another cost saving measure.

[JcLusso]

Originally Posted by schnazzy

This is an interesting read....

First I'd like to thank the OP JcLusso, for putting this together was an effort and it is appreciated. Also, TPG for responding was classy.

If JcLusso wouldn't mind taking some constructive thoughts... because of some of the extreme statements and in particular a couple conclusions like TPG asking about what materials another company used and trying to stretch that to the conclusion that TPG doesn't know anything actually reduces my believe in your other statements. If you stetched there, where else?

Also, the extreme statement just cause flame wars and if that was what you were after, ok, cool, job done but that much work, I'd assume you really wanted to help the community so having a less biased tone and coming at it with full disclosure and a mediated tone would strengthen your post.

Having said that, again, appreciate the work and the post. I'd definitely like to see more car stats.

No problem!

As far as my statements being extreme, they are all backed by the posts in multiple other threads. To keep the main post from being too long I didn't include every piece of evidence there was because that would just be overkill. If you want to really see how I know TPG has no idea what they are doing you can read some of the posts from the other thread where Boss330 and a few other members really ran them into the ground. Skim through it and you'll see around page 3-5 they start to get torn apart, back peddling on their previous statements and start ignoring questions and answering what they want.

http://f80.bimmerpost.com/forums/sho....php?t=1222431

As far as my biased tone, I have no secondary motivations besides helping this community. I'm not a vendor and have nothing to sell.

[larryn]

Originally Posted by JcLusso

As far as my biased tone, I have no secondary motivations besides helping this community. I'm not a vendor and have nothing to sell.

It would be fantastic if you could create a summary of this summary thread. (Sorry - couldn't help myself!)

[JcLusso]

Originally Posted by larryn

It would be fantastic if you could create a summary of this summary thread. (Sorry - couldn't help myself!)

The main thread has been updated multiple times with new information from the comments. You really are too funny though. Maybe you should consider comedy as a profession!

[9SECDD]

Originally Posted by FIRSTM3NYC

First I must say I am no mechanic.... I will just stat the facts.

I am one of the guy that bought the TPG crank hub. I even had them install it. I had no crank hub issues before hand, car was perfectly fine. I had it installed as a preventative measure as TPG indicate... To this day my car is running perfectly fine with no issues.

Car:
F80 M3 Dct

Current Mods:
TPG Hub
dps
er charge pipes
meth
jb4
pure turbo stage 2
Dodson clutch packs

I don't track the car.
it is a daily driver.
I do drive aggressive but within reason, meaning I don't redline. no burn outs. Im more of a spirited driver.
My build date is 4/15/2015.

besides the installation on the TPG Hub and clutch packs, Only one tech touched my car.

Hopefully we can resolve the crank hub issue and move forward with this platform.

Of course if my crank hub goes I will let you guys know.

#resolvethisissuetogether

I have the virtually the exact same mods (except different turbo brand because my shop preferred it, even though I think Pure Turbos and Jesse are awesome), minus the meth. Also have the TPG hub installed. Not going to sweat it. Will post if something happens.

How do you like meth? Is it a pain? Not a pain? Big difference with larger turbos vs. turbos with no meth? I'm trying to avoid meth, but open-minded.
You run a custom map 6?

[FIRSTM3NYC]

Originally Posted by NJ-M4

I have the virtually the exact same mods (except different turbo brand because my shop preferred it, even though I think Pure Turbos and Jesse are awesome), minus the meth. Also have the TPG hub installed. Not going to sweat it. Will post if something happens.

How do you like meth? Is it a pain? Not a pain? Big difference with larger turbos vs. turbos with no meth? I'm trying to avoid meth, but open-minded.
You run a custom map 6?

There is a big difference with meth... and yes I am running a custom map

[E92 nick]

BUMP

[chillindrdude]

Originally Posted by FIRSTM3NYC

Car:
F80 M3 Dct

Current Mods:
TPG Hub
dps
er charge pipes
meth
jb4
pure turbo stage 2
Dodson clutch packs

I don't track the car.
it is a daily driver.
I do drive aggressive but within reason, meaning I don't redline. no burn outs. Im more of a spirited driver.
My build date is 4/15/2015.

Damn son. Your car sounds well sorted. It's gotta be pushing 600+ whp?

I would definitrly do the crank hub mod for stg 2 and higher mods.

[Dan@BPC]

Originally Posted by Boss330

Agree that my wording "purely for assembly" was a bit to conclusive

However, I feel that the crank design of the new modular engines, with a machined sprocket integrated in the crank, kind of weakens the argument regarding money shifting. The new design does not allow slippage so it does not have that "function" designed into the valve drivetrain...

So it seems they do not think slippage is a necessary safe guard, at least not on the new modular engines...

Hey Boss, been following this thread. You have added a lot of value to this topic. I feel along with what you stated above another main reason why the crank is not keyed is there is not longer a removable front cover on any of the Nxx 6 cyl engines. Because the front cover is now part of the block the manufacturing process has now been simplified. No additional front cover gasket, No addition front cover bolts, No water pump to be installed and the whole timing chain assembly is dropped in from up top. Then as you stated the robots come in and torque the bolts down.

So to sum it up IMO top reason why they choose this.
1. Cheaper to manufacture ( faster to assemble and less parts)
2. Block is overall stronger (less NVH)
3. Lighter (magnesium and aluminum blend)
4. Oil leaking from front cover will never be an issue to be paid out under warranty ever again. (Even though never really was an issue)
5. If timing guides fail under warranty less labor is involved to replace.

I have been solely servicing BMW's since 2002. 10 of those years has been under their roof at the dealer. BMW just like every other car manufacture builds there product to make it out of warranty. After out of warranty it is no longer there problem. That is why when you take you BMW to the dealer once out of warranty ONLY that dealer has record of it. It is not shared with anyone else. If BMW comes and does an audit of the dealer they do not look at 1 single customer pay ticket. They don't care about anything that they don't have to pay for. Same reason why the phone call from BMW that effects their CSI (customer survey index) is only for cars under warranty not for customer pay cars.

Hope this sheds some more light on this topic for you guys.

Dan

Edit: If the question comes up why they moved the chain to the rear on the B58.
1- BMW only runs an engine for so long before it is timed out.
2-You guys have already answered that in this thread. BMW knows if they want to make more power and not have warranty issues the current design needed to be changed/updated.

[dmk08]

So did anyone notice the TopGear ZCP article says that "The engine crank case cover has had to be uprated to cope, but nothing else has, and in terms of character and delivery not much has changed.". Does anyone know exactly what parts were changed?