[moonshine89]

Originally Posted by Proctor750

Hang on, is the bolt "dissolving" or backing out? Which is it?

If it "dissolves" couldn't someone source a stronger bolt?

If it backs out - can't you add 272, increase torque and safety wire?

I simply want to understand what is happening and if the bolt is the culprit.

Haven't heard of the bolt dissolving. Backing out was reportedly and issue due to vibrations. But again, many have had perfectly torqued bolts w/ failures in the friction washer.

[Nigelo]

Just to throw a potentially related thing into the mix ... My M4 has been delayed at the last moment, BMW are doing so as a precaution but it has something to do with needing to fit a new crankshaft position sensor....

[Proctor750]

I'm wondering if the spline lock fix is better than the keyed solutions or not. The keyed solutions look logically like a better solution but I can see how using essentially a reversed "EZ out" would keep it from moving as well.
It just seems like the keyed variants are machined to an exact lock position where the spline lock is basically digging into material to hold it.

[akkando]

Originally Posted by Davil

M2 DCT Software is revised and shifts have no “slam” compared to previous models at full tilt. Part of a bigger picture? Who knows.

I was wondering about this. Why did they retune this? If it was to reduce chance of SCH I would think they would also tune all the DCT M cars this way with the latest update, but I don't think they have.

[FSociety]

Originally Posted by Proctor750

I'm wondering if the spline lock fix is better than the keyed solutions or not. The keyed solutions look logically like a better solution but I can see how using essentially a reversed "EZ out" would keep it from moving as well.
It just seems like the keyed variants are machined to an exact lock position where the spline lock is basically digging into material to hold it.

I recommending email or asking VTT directly.
Also these folks over at EAS have done a few Spline Lock https://f80.bimmerpost.com/forums/sh....php?t=1561598

[M2C_PLUS]

Originally Posted by Davil

M2 DCT Software is revised and shifts have no "slam" compared to previous models at full tilt. Part of a bigger picture? Who knows.

Originally Posted by Karmic Man

Nice call on this one, could well be the case...

Originally Posted by akkando

I was wondering about this. Why did they retune this? If it was to reduce chance of SCH I would think they would also tune all the DCT M cars this way with the latest update, but I don't think they have.

Makes no difference. Crank hubs have spun on stock M2C's

[///M Houbi]

Originally Posted by GreatWhiteM2

Makes no difference. Crank hubs have spun on stock M2C's

How many so far? What mileage?

🤮

[M2C_PLUS]

Originally Posted by ///M Houbi

How many so far? What mileage?

🤮

1300ish miles

[Proctor750]

Originally Posted by GreatWhiteM2

1300ish miles

Who did this happen to? You?

What was the failure point? bolt backing out? washer? Did it cause physical damage or only slip a deg?

[M2C_PLUS]

Originally Posted by Proctor750

Who did this happen to? You?

What was the failure point? bolt backing out? washer? Did it cause physical damage or only slip a deg?

It is the bolt every time. When you see the design first hand you know why. The moment the friction ring breaks contact with the the timing sprocket, the timing sprocket is out of time with the crank.

It only needs to loosen enough for the timing sprocket to move 3mm and thats the timing out and limp mode. See the image of the damage to my timing sprocket. Those marks are only around 3-4mm long, enough to throw the timing out only. I was cruising at 45-50mph in top gear when mine went. So very lucky.

[Proctor750]

Originally Posted by GreatWhiteM2

It is the bolt every time. When you see the design first hand you know why. The moment the friction ring breaks contact with the the timing sprocket, the timing sprocket is out of time with the crank.

It only needs to loosen enough for the timing sprocket to move 3mm and thats the timing out and limp mode. See the image of the damage to my timing sprocket. Those marks are only around 3-4mm long, enough to throw the timing out only. I was cruising at 45-50mph in top gear when mine went. So very lucky.

Wow, so it sounds like it was weakening long before it finally gave way. For it to systematically fail in such a way it's strange the occurrences are so sporadic. I wonder what the difference is between a car in which it doesn't fail and yours? The bed plate change clearly didn't fix anything.

[doughboy]

Such a strange design. It must be to simplify build or initial timing setup, can't think of any other reason for it..

[Proctor750]

Originally Posted by GreatWhiteM2

It is the bolt every time.

Also: If it is indeed the bolt each time - why does the VVT crank capture piece not solve the issue? Why do you also need the EZ out carved hub? Assuming the capture holds the bolt from backing out -how can the hub help?

[doughboy]

Agree - fitting just the bolt capture plate seems an easy job and if it stops the bolt coming loose that's good. but.....

There are multiple areas that movement could occur. The friction washer sits only between hub and timing gear see https://www.realoem.com/bmw/enUS/sho...diagId=11_5597

1. The timing gear could slip on the hub (less likely due to friction washer between them)

2. The hub could move against the crank moving the timing gear with it. If the hub turns then this may turn the bolt with it maybe loosening the clamping further

3. Both of the above at the same time

The vibration damper is very heavy and this puts a lot of rotating mass on the hub.

[FSociety]

Originally Posted by Proctor750

Also: If it is indeed the bolt each time - why does the VVT crank capture piece not solve the issue? Why do you also need the EZ out carved hub? Assuming the capture holds the bolt from backing out -how can the hub help?

The VTT Bolt Capture has been around since 2017 back then Gintani or Maxpsi hub wasn't out.
There's a PS2 F80 M3 with Meth and E50 fuel running over 15,000 miles on that bolt capture ($100 piece) since August 2017 after he spun oem hub twice w/o any preventative protection.
Now VTT released a Spline Lock Hub (full fix, and only one that does not require drilling unlike Gintani/Maxpsi hub)

More options better for the platform

[Proctor750]

Originally Posted by FSociety

The VTT Bolt Capture has been around since 2017 back then Gintani or Maxpsi hub wasn't out.
There's a PS2 F80 M3 with Meth and E50 fuel running over 15,000 miles on that bolt capture ($100 piece) since August 2017 after he spun oem hub twice w/o any preventative protection.
Now VTT released a Spline Lock Hub (full fix, and only one that does not require drilling unlike Gintani/Maxpsi hub)

More options better for the platform

While I agree that more options are always the best - this sentence here tells me either the bolt capture is all you need OR he was lucky (not enough data).

$100 bolt capture vs $800 hub + 20 hours of labor.... I may just spring for the capture and hedge my bets no?

I wish there was more data on people using just the capture piece. If it provides even 80% success rate vs the 100% of the full spline lock option - at $100 bucks you are hitting diminishing returns with the spline lock.

[doughboy]

Originally Posted by Proctor750

While I agree that more options are always the best - this sentence here tells me either the bolt capture is all you need OR he was lucky (not enough data).

$100 bolt capture vs $800 hub + 20 hours of labor.... I may just spring for the capture and hedge my bets no?

Some logic there maybe. The bolt capture effectively "keys" the hub to the bolt (but neither to the crank).

We don't know for sure if the bolt is coming loose, or if the hub slips while the bolt remains static and in factory position.

Either way the bolt capture locks them both together which will greatly increase the torque load required to slip the hub and bolt "as one" and will prevent bolt movement on its own.

[Proctor750]

Originally Posted by doughboy

Some logic there maybe. The bolt capture effectively "keys" the hub to the bolt (but neither to the crank).

We don't know for sure if the bolt is coming loose, or if the hub slips while the bolt remains static and in factory position.

Either way the bolt capture locks them both together which will greatly increase the torque load required to slip the hub and bolt "as one" and will prevent bolt movement on its own.

That's the thought. If it's the bolt then the capture should do it but it attaches to the hub face and not the crank so as you said they are static and depend on the issue being the bolt backing out.
Its starting to sound like a high rpm resonance thing and not so much HP related. It's extremely unusual to me that a 100% demonstrable culprit has yet to be agreed on with such an obvious sampling of incidents. I guess diagnosis isn't pursued and as in many other things the attention is given to the symptoms and not the actual cause.

[Karmic Man]

Originally Posted by Proctor750

That's the thought. If it's the bolt then the capture should do it but it attaches to the hub face and not the crank so as you said they are static and depend on the issue being the bolt backing out.
Its starting to sound like a high rpm resonance thing and not so much HP related. It's extremely unusual to me that a 100% demonstrable culprit has yet to be agreed on with such an obvious sampling of incidents. I guess diagnosis isn't pursued and as in many other things the attention is given to the symptoms and not the actual cause.

Yes I also believe it’s high rpm related and that explains why the N54 and the N55 had a much lower incident of this event as they have a lower redline.

[M-Pilot]

Originally Posted by Proctor750

That's the thought. If it's the bolt then the capture should do it but it attaches to the hub face and not the crank so as you said they are static and depend on the issue being the bolt backing out.
Its starting to sound like a high rpm resonance thing and not so much HP related. It's extremely unusual to me that a 100% demonstrable culprit has yet to be agreed on with such an obvious sampling of incidents. I guess diagnosis isn't pursued and as in many other things the attention is given to the symptoms and not the actual cause.

Yup, exactly! Tony from VTT also says it's more RPM related:

[M2C_PLUS]

Originally Posted by Proctor750

That's the thought. If it's the bolt then the capture should do it but it attaches to the hub face and not the crank so as you said they are static and depend on the issue being the bolt backing out.
Its starting to sound like a high rpm resonance thing and not so much HP related. It's extremely unusual to me that a 100% demonstrable culprit has yet to be agreed on with such an obvious sampling of incidents. I guess diagnosis isn't pursued and as in many other things the attention is given to the symptoms and not the actual cause.

It is along those lines. Using the bolt capture to clamp the bolt to the hub effectively makes "one big bolt" out of the bolt and crank hub. It can still come undone if the vibrations are excessive enough. So having crank hub keyed to the crank also is the perfect combo.

Having seen an S55 engine on a bench dyno the damper rotation is far from smooth and is only exaggerated as RPM's increase.

[doughboy]

They call it a "damper" but in my experience they are just a big heavy metal lump of a pulley, a mini flywheel on the front of the crank. No flexible parts are there. It's meant to dampen out torsional (twisting) vibrations in the crank.

Looking logically, a sudden increase in (clockwise) crank rpm would place a strong anticlockwise (ie undo right hand thread) force on the hub. Conversley a sudden decrease in rpm would apply force to tighten the hub. This may go some way to explaining the slipping on it money shifts and kickdowns.

Also higher frequency back and forth twisting oscillations will put a lot of stress on the hub assembly. These will increase with engine torque at any given rpm as extra torque directly applies force at every firing stroke to the crank causing flex that the damper has to damp. BMW will have tested this for sure, but only for their designed torque ranges.

Checking on TIS the centre bolt (TTY stretch bolt) is tightened to 100nm plus 270deg.

Also it says to oil the thread and no thread locking compound is used. So the assembly relies on the friction of the hub/gears/crank faces only.

Oiled threads will clamp much tighter at a given torque however. It says should be over 600nm to remove.

For 99USD plus shipping the VTT bolt fix seems a good start.