Crank Bolt Capture and still spun crank hub?

[Chris@VargasTurboTech]

Originally Posted by Hoppyumr

I know what you are trying to say, but here's my take on it. I'm going to make something up, so hopefully it makes a slight sense. It's not a perfect analogy but I think the moving parts work well enough; don't beat me up too much if it doesn't make sense to you - just trying to help Parle realize that adding a device bolted stirringly to something that can still move seems relatively pointless to me at least.

Imagine setting a mirror down on a lazy Susan, you know the type that spins on table, and the lazy Susan is sitting on a round table. Because you really don't want the mirror to move you add a big bracket between the table top and the lazy Susan using really heavy duty grade 12 bolts. The reason we did all this was so while sitting at our home office we can still see the football game. That should solve it, right, the mirror is placed just right so we can see the game - nothing will move, and it'll all be perfect. But wait, your girlfriend/wife suddenly decided to rearrange the kitchen including spinning the table around, and because the table moved now you can't see the game anymore without repositioning things the way they were. If the wife/girlfriend was really mad you did all this to see the game she might just break your mirror altogether... 😜

While it's not perfect, hopefully you see the analogy I came up with here.

1. Floor = crankshaft
2. Table = crank hub
3. Lazy Susan = Harmonic balancer
4. Bracket between table and lazy Susan = CBC
5. Bolts= well, the new hub bolts holding the CBC
6. Mirror = timing cog
7. Setting the mirror on the lazy Susan = diamond sintered friction discs (note we didn't change anything here)
8. Moved mirror = engine out of time,
9. Seeing the game = engine perfectly in time
10. Wife/girlfriend = unexplained reason for spun crank hub failures
11. Wife/girlfriend breaking mirror = engine destroyed

The thing we didn't really change here was the thing holding the table in position, aka static friction. The only way to change static friction is to change the coefficient of friction, or change the force acting on the coefficient of friction. In this case, increased coefficient of friction could be by use of pins or potentially (not saying it works or not) splined hub, or could be by overtighting the crank bolt (same as making the above table much heavier such that the wife/girlfriend couldn't move it. The timing cog could even be welded or pinned in place, but if the assembly is allowed to shift at all, then the intent has failed. Nothing in the CBC solution done alone has increased the static friction between the timing cog and the hub.

I'd be interested to know why BMW thought it a good idea to create this "mechanical fuse" in the engine.

Dang that analogy hurt to read.

That said, CBC doesn't increase clamping force, it simply stops the bolt from vibrating loose. If the friction capability of the design (bolt torque intact) is insufficient for the load, the CBC will not stop a spin.

This is why we say the CBC does a great job in reducing the risk, but the complete solution is a spline lock and the CBC working together in beautiful, sweet harmony.

[Hoppyumr]

Originally Posted by Chris@VargasTurboTech

...
That said, CBC doesn't increase clamping force, it simply stops the bolt from vibrating loose. If the friction capability of the design (bolt torque intact) is insufficient for the load, the CBC will not stop a spin.
...

Yah, unfortunately I didn't say it'd be easy to read. I challenge you to come up with another analogy. I'd love to see what you come up with. 😎

Sounds like you generally agree on some points; however, I disagree fully with your statement that it stops it from working loose. What you are referring to with capture plates being used all over on industrial machines is true, but the implementation is entirely different and the substrate the capture is mounted to is fixed and doesn't rely on a friction disc. All torque still runs through the friction disc(s).

[Chris@VargasTurboTech]

Remember, 2 mechanisms.

1) Bolt vibes loose, reducing clamping force, reducing holding capacity = spin
2) Outright overcoming friction capacity of design = spin

If, through various shock loads, the bolt torque is reduced, the holding capacity of the design is correspondingly reduced and you get to #2 above, but through #1. CBC stops this mechanism. It simply stops the bolt from being able to turn relative to the assembly unless you have failure mode #2, in which case you still get a spin. Another way of looking at it is the CBC allows the OEM design to work to its' maximum potential. The CBC + splinelock extends this to much higher levels.

Hence why the complete solution is CBC + spline lock blah blah blah.

[Kstoff125]

Originally Posted by Chris@VargasTurboTech

Remember, 2 mechanisms.

1) Bolt vibes loose, reducing clamping force, reducing holding capacity = spin
2) Outright overcoming friction capacity of design = spin

If, through various shock loads, the bolt torque is reduced, the holding capacity of the design is correspondingly reduced and you get to #2 above, but through #1. CBC stops this mechanism. It simply stops the bolt from being able to turn relative to the assembly unless you have failure mode #2, in which case you still get a spin. Another way of looking at it is the CBC allows the OEM design to work to its' maximum potential. The CBC + splinelock extends this to much higher levels.

Hence why the complete solution is CBC + spline lock blah blah blah.

Chris, looking to have a shop in Ferndale, MI install a VTT CBC, what is a reasonable amount of shop hours for this? I’ve seen everything from 2-4...haven’t gotten the quote yet but they quoted me ~$800 to install downpipes so I’m anticipating a lot more hours than what the general consensus is...thanks!!!

[Chris@VargasTurboTech]

We don't quote hours as it really depends on the shop but 4 is definitely reasonable as an hour estimate.

[fivaxis]

Originally Posted by Hoppyumr

Yah, unfortunately I didn't say it'd be easy to read. I challenge you to come up with another analogy. I'd love to see what you come up with. 😎

Sounds like you generally agree on some points; however, I disagree fully with your statement that it stops it from working loose. What you are referring to with capture plates being used all over on industrial machines is true, but the implementation is entirely different and the substrate the capture is mounted to is fixed and doesn't rely on a friction disc. All torque still runs through the friction disc(s).

You’re forgetting the clamping pressure in your analogy. Imagine the round table weighs 5000 lbs, how is your wife going to move it? The only way you can make the table weigh less is to rotate the lazy Susan. Which is why you bolted the lazy Susan to the table with the big bracket.

[M3F80Art]

Originally Posted by landonvan

Her is my take on the whole thing. In every case I have read when the crank spins. The bolt is loose. Not one shop has said that the bolt was still factory tight but the hub still spun. And from this forum I have only found a few. And I mean a few like on one hand, people that spun their hub with just the CBC. Some have spun with both. But they are in 800hp/Tq. Range. So at that point any week link is subject. I have Vargas GC. Making over 600hp. I don’t drive like an ass but I enjoy my car. I just have the CBC. No plans on doing anything more. And I’m at 67k miles.
And for the guy that can’t find a shop. Come down the Virginia. I’ll do it for you. At my shop.

I have a 2015 M3 F80 6speed manual trans with Active autowerke catless downpipes paired with AA single midpipe and Mst Air intakes,Ftp charge pipes and J pipe , Ngk laser iridium 97506 . MHD OTS tune stage 2 560 hp… before i installed the VTT CBC i torqued the crank bolt with the help of another person, felt like a barely turned the bolt honestly … anyways cars pulling hard far from stock and have had 0 issue’s done multiple 60-130mph pulls feels good

[sonicnofadz]

I know this thread has been dead a while, though I thought I might just chime in. I come from the n54 world and have recently bought a low mileage f80 (still have my e90 335i). Its been pretty well documented on N54's that the CBC doesn't work that well, a ton of guys with the VTT cbc have seen it fail, not sure about the other ones out there. Not sure I'd trust it on the s55 either but YMMV.

[Info@mad-us.com]

Originally Posted by sonicnofadz

I know this thread has been dead a while, though I thought I might just chime in. I come from the n54 world and have recently bought a low mileage f80 (still have my e90 335i). Its been pretty well documented on N54's that the CBC doesn't work that well, a ton of guys with the VTT cbc have seen it fail, not sure about the other ones out there. Not sure I'd trust it on the s55 either but YMMV.

Do a pinned Crank Hub and don't worry about it ever again.

[sonicnofadz]

Originally Posted by Info@mad-us.com

Do a pinned Crank Hub and don't worry about it ever again.

Yes, my sentiment exactly

[sonicnofadz]

These are all VTT n54 cbc failures (apparently the bolts they supply are wuhan garbage). You've been warned

[wheela]

I enjoyed the lazy suzan analogy! My analogy is a bolt and washer. In the analogy the bolt is the crank bolt, the washer is the crank hub, and what the bolt is screwed into is the crankshaft. I think putting a CBC on your crank hub to stop the crank bolt from loosening is kind of like if you welded the bolt head to the washer in the analogy to stop the bolt from loosening. The bolt is rotationally locked to the washer via the weld, but the whole works can still unscrew together. Same with the crankhub and crankbolt - they can be rotationally fixed to eachother via the CBC, but the whole works can still unscrew from the crankshaft together as one big assembly.

[wheela]

I am glad that nobody here with just CBC has spun their hub👍

[Info@mad-us.com]

Originally Posted by wheela

I enjoyed the lazy suzan analogy! My analogy is a bolt and washer. In the analogy the bolt is the crank bolt, the washer is the crank hub, and what the bolt is screwed into is the crankshaft. I think putting a CBC on your crank hub to stop the crank bolt from loosening is kind of like if you welded the bolt head to the washer in the analogy to stop the bolt from loosening. The bolt is rotationally locked to the washer via the weld, but the whole works can still unscrew together. Same with the crankhub and crankbolt - they can be rotationally fixed to eachother via the CBC, but the whole works can still unscrew from the crankshaft together as one big assembly.

Pretty much. Also keep in mind the bolt is reverse thread.

[Marioec]

How many people here are still running strong on CBC and not spun there crank hub ?

[todd20]

Ive spun mine with cbc on stock crank hub

E85 tune with pures 500-600hp

[Beemerm3]

so there are reports that the vtt cbc is breaking down. but the thing is people arent using an endoscope camera to look inside there crank hub to see if their bolts are broke down also. its probably not noticeable. the camera is like 20 bucks on ebay btw.