First reported pinned crankhub failure (with photos)

[fivaxis]

Accessories take how much torque to run? Seems negligible to me.

[ILoveCugars]

Your also driving 2 hpfp, vacuum pump and larger oil pump system. N55 dont have as much drag on the timing chain system and is a reason why spun hub is not near as common.
Dct ability to change rpm large amounts so fast adds to it as well.

[jpy1980]

I wonder if this was the guy that spun haha look at his plates.

[swagon]

Originally Posted by jpy1980

I wonder if this was the guy that spun haha look at his plates.

This is why I don't hang out with other BMW/M guys, revving a burble tuned ricer in the middle of the city for the 'gram ain't my thing

It's the owner of the shop behind the wheel in that ymb car

[HyeM3]

Originally Posted by jpy1980

I wonder if this was the guy that spun haha look at his plates.

That car used to belong to the owner of the shop that supposedly installed OP's hub. Guy posts vids on Instagram and YouTube of him driving customers' cars the same way...

[jpy1980]

Haha why does that car sound like that? No bass all treble. Sounds horrible.

[MisterF80M3]

Originally Posted by jpy1980

I wonder if this was the guy that spun haha look at his plates.

Gotta give credit where credit is due though. He made an embarrassment turn into something pretty sick

[MJ6]

Originally Posted by ILoveCugars

There is nothing preventing the hub from spinning with only a CBC. It helps keep maxium clamping force on the hub but if you exceed that break away torque the hub will spin. Helps yes.. guaranteed no...

100% correct. If the hub bolt is torqued correctly, the CBC will help prevent any engine harmonics or load shocks from backing it out, essentially ensuring a static clamping force.

The data I'm waiting to see though is at what load/torque does the shearing force overpower the friction disks? If the clamp load is held constant, it should be an easy enough experiment to bench test, especially seeing that VTT had a test rig set up at one point in time to test their spline lock fix. Clutch manufactures are able to provide an estimated clamping load force based on a friction coefficient, so I'm curious as to why the same principle hasn't been applied in this situation.

I'm not denying that pinning or splining your hub creates a more permanent solution, but for some we need more solid data other than a vague "it could happen to you if you don't" to justify the additional cost.

[fivaxis]

Now you’re talking, break away torque for the bolt is 440 lbs so with the friction surfaces it would have to take more than that to spin the hub. I think there is a reason we’re not seeing CBC only cars spin the hub.

[ILoveCugars]

Originally Posted by MJ6

100% correct. If the hub bolt is torqued correctly, the CBC will help prevent any engine harmonics or load shocks from backing it out, essentially ensuring a static clamping force.

The data I'm waiting to see though is at what load/torque does the shearing force overpower the friction disks? If the clamp load is held constant, it should be an easy enough experiment to bench test, especially seeing that VTT had a test rig set up at one point in time to test their spline lock fix. Clutch manufactures are able to provide an estimated clamping load force based on a friction coefficient, so I'm curious as to why the same principle hasn't been applied in this situation.

I'm not denying that pinning or splining your hub creates a more permanent solution, but for some we need more solid data other than a vague "it could happen to you if you don't" to justify the additional cost.

I think that is a tough one, you can figure out the break away torque required to spin the hub as a steady applied torque but the drag on the hub is applied much more erratically. There is going to be added shock load that is applied when the inertia the valve train/ accessories has dramatically changes in milliseconds. Wheel hop, kick down mode, misshifts all would add a lot of shock load. How much more though is going to be a pretty tricky to figure out, or at least math over my head.

[PhatLyfe]

Originally Posted by jpy1980

I wonder if this was the guy that spun haha look at his plates.

Unnecessary or over excessive bangs make it sound like he's running the car on bad/cheap gas.

[GreenGoblin]

I remain skeptical. Who is to say these pins in a pinned hub will not just shear off at high rpm, or during a kick down. I cannot even find one shear stress chart or any real engineering data besides someones "word". Please link if u have any.

[MR RIZK]

Originally Posted by GreenGoblin

I remain skeptical. Who is to say these pins in a pinned hub will not just shear off at high rpm, or during a kick down. I cannot even find one shear stress chart or any real engineering data besides someones "word". Please link if u have any.

There is no data and not sure how this will help in your decision process. Even if a manufacturer listed the value you would need all manufacturers to release the same data to help make a choice.

Since the pinned solution removes the friction ring imo the ideal solution is a combination of the pinned design and the splines. Provides best of both worlds.

[jpy1980]

Originally Posted by MR RIZK

There is no data and not sure how this will help in your decision process. Even if a manufacturer listed the value you would need all manufacturers to release the same data to help make a choice.

Since the pinned solution removes the friction ring imo the ideal solution is a combination of the pinned design and the splines. Provides best of both worlds.

The splines are installed as an interference fit. The tolerance for the pins alone going into the crank is pretty tight (as seen with this failure), so don’t think that’s going to work. I mean the pin and spine design isn’t patented so I’m think one of these vendors would of thought of doing both, no?

What about welding the pieces all together haha

[Bmwlmr99]

92,000 miles stage 2 tune since 28,000miles...full exhaust. down shift , do 40, 50 60 mph rolls against mustangs, zl1 Camaros zo6 vettes etc....NO crank hub mod, at all...nothing....

[coldsteelrain]

Originally Posted by Bmwlmr99

92,000 miles stage 2 tune since 28,000miles...full exhaust. down shift , do 40, 50 60 mph rolls against mustangs, zl1 Camaros zo6 vettes etc....NO crank hub mod, at all...nothing....

This shows that it does not impact everyone and instead of it being an engineering issue it's most likely an issue that arises at engine assembly.
Probably not torqued right or some minor detail
Will we ever know?

[MR RIZK]

Originally Posted by jpy1980

The splines are installed as an interference fit. The tolerance for the pins alone going into the crank is pretty tight (as seen with this failure), so don't think that's going to work. I mean the pin and spine design isn't patented so I'm think one of these vendors would of thought of doing both, no?

What about welding the pieces all together haha

The splines are inside the snout and the pins on the front face. You don't need the splines all the way round ie no splines where the pins are. The issue will be how do u ensure the pins line up the while pressing it in for the interference fit of the splines. Lots of room for error

[jpy1980]

Originally Posted by MR RIZK

The splines are inside the snout and the pins on the front face. You don't need the splines all the way round ie no splines where the pins are. The issue will be how do u ensure the pins line up the while pressing it in for the interference fit of the splines. Lots of room for error

That’s actually a good idea!

What about instead of an interference fit, use a press tool to initially make the opposing splines on the crank and then drilling the pins, and then sliding in the new hub? Or is what makes the splines work is the interference fit?

[MR RIZK]

jpy1980 ideally the splines should be milled like the half shafts on the rear axle or input shaft. There is no room to do this. What VTT is doing by pressing the splines is they get an exact fit at time of install.

[Nisse Järnet]

Yeah, it would be really interesting to compare how much torque it takes to break a OEM hub to a pinned/splined one.
On turbo M50 engines people sometimes break the woodruff key and spin the hub too.

[MJ6]

Originally Posted by Nisse Järnet

Yeah, it would be really interesting to compare how much torque it takes to break a OEM hub to a pinned/splined one.
On turbo M50 engines people sometimes break the woodruff key and spin the hub too.

Unfortunately I don't think that's something that we will ever see.

It's obvious that test rigs can be constructed and have been used in the past to validate crank hub "solutions", however if qualitative data was released which specified that if within a certain power level (given that the crank bolt was torqued to factory specifications) the hub had a less likely chance of spinning, it would essentially equate to a loss of revenue for those selling and installing these "fixes".

Hard numbers and proven facts are the antithesis of marketing through alarmism, unfortunately they're not always embraced if they would prove detrimental to business.

[Chris@VargasTurboTech]

It's actually a trickier question that what torque does it slip at. Remember, these hubs don't see engine torque, at least not like they're a clutch. They see load from spun accessories, cams, pumps, etc. Rate of change is the big driving thing... which goes up with increased power levels too (you accelerate quicker, go through rev ranges quicker). RPM plays a significant role. We have actually slipped hubs doing no boost pulls on the dyno testing things, spun it up to 8K on the shop N54, dyno read 350WHP, and it came down with crank to cam correlation codes. You can't always put a power number on it. I acknowledge that it would make go/no-go points much easier, but unfortunately that line of thinking is a significant oversimplification of what's really going on.

The complete solution doesn't always make sense but it's always the complete solution. It's about managing risk. Yes, it's the sure-fire way to retire the risk, but for example recently I was contacted via PM here on this site by a guy with a stock tune, no power mods, still under warranty for 2 years, asked me my honest opinion about doing a hub. I told him I wouldn't bother with a hub in that situation, maybe a CBC to avoid the possible hassle, but drive it and if it slips, make BMW pay for it. The magic words there were "no tune" and "warranty". Once out of warranty, particularly if he wanted to dive into more power goals... then his risk increases. At that point, give me a call and let's revisit the subject if he still has the car and wants to push harder. For now? Drive it. I do calls/consults like this all the time -pretty straight forward. Remember the best customers are long term customers.

Chris