Z4m vanos exhaust hub failure

[Calichase]

Well, not how I planned this to occur, but glad it happened the way it did.

In preparation for a supercharger install and for clear piece of mind on the track I decided to perform preventive maintenance on the m coupe (which has around 70k miles and 15 track days).

I planned to replace the rod bearings with a treated variant, and replace the vanos bolts and rod bolts with oem versions. While inside I found one of the exhaust hub's pins to have sheared, luckily in a manner that still allowed it to make some contact and perform its function (although not for very much longer). The vanos pump's bearings were in fine, working order so the cause of the shearing is not immediately obvious.

Going to replace with a cryo treated unit and see how it turns out. Luckily it failed and was noticed quickly.

[racerbruce]

Wowie -
Fortuitous timing; what is cyro?

[dc_wright]

Originally Posted by racerbruce

Wowie -
Fortuitous timing; what is cyro?

He meant cryo. Cryogenic treatment of metals is a relatively new process for increasing certain desirable properties that can be obtained through heat treating.

https://en.wikipedia.org/wiki/Cryogenic_hardening

[racerbruce]

Thank you -
Does knowledge of the metallurgical makeup of the part to be treated need positive ID prior to considering cryo treatment to ensure compatibility?

[NickyC]

Wow, nice catch!!

[dc_wright]

Originally Posted by racerbruce

Thank you -
Does knowledge of the metallurgical makeup of the part to be treated need positive ID prior to considering cryo treatment to ensure compatibility?

Absolutely. If you have a part made from a material that doesn't benefit from extreme cold work hardening, all you've done is wasted some liquid nitrogen.

[racerbruce]

Couldn't the cryo treatment permanently (negatively) alter metallurgical structure of the metal?

[Vanne]

It's a well known issue Cali. The tabs shear due to the fact that the hub holes are too big, thus the tabs "rattle" in the hub. Glad you caught it mate. Much longer than that and the costs would have considerably increased.

There are various offerings from a few different manufacturers. Don't just fix the hub, the pump disc needs attention too. Besian and Dr vanos offer solutions. Inspections should not be further than 60k miles apart.

Once again mate, bloody awesome you caught it.

[dc_wright]

Originally Posted by racerbruce

Couldn't the cryo treatment permanently (negatively) alter metallurgical structure of the metal?

It depends on what you're trying to achieve. It significantly increases hardness so it's appropriate for parts that are in moving contact, but it also increases brittleness so it may make parts that experience high shock loads more likely to fail.

[Vanne]

This is why the revised pump disc from besian is a great idea, and you get cash back for your old one of its not shagged.

[Shutterspeed]

I'm still pretty new to the whole VANOS issues. What's a good idea in terms of preventative maintenance and lower end (cost wise) upgrades for the unit?

[Calichase]

There's primarily two common failures.

One being the bolts holding the cam gear and hub (inside the vanos unit) can either shear off, or back out. That's a pretty simple fix if you are carefully to not disturb cam timing. Just talking one bolt out and replacing it with a recommended variant and torquing them. I got all the bolts with loctite from ecs for under $30. Then you need a vanos gasket and valve cover gasket, and should probably replace all vanos unit seals/ o rings and perform a valve adjustment while you are in there.

The other common issue is the exhaust hub pins shearing off. This is most likely caused from the pins being a bit smaller then the female holes they insert into (inside the oil pump disk in the vanos unit). Best course of action is getting a strong exhaust hub (a cryogenically treated variant, can be found by a few guys on m3forum for ~$650 or dr vanos for 950). Also getting a remachined oil disk with new, smaller holes will Eliminate any play that caused the pins to shear (also got mine off the forums for under 100).

A few other problems can happen, such as the entire vanos unit failing or more specifically the vanos solenoid. But the previously stated issues are what you can address now.

[StickMon]

Originally Posted by Calichase

... the bolts holding the cam gear and hub (inside the vanos unit) can either shear off, or back out. That's a pretty simple fix if you are carefully to not disturb cam timing. Just talking one bolt out and replacing it with a recommended variant and torquing them. ...

Careful there. The bolts that shear hold the splined sleeve inside the hollow camshaft.
To get to those bolts you have to remove the sprocket hubs.
Once you undo the hubs you disturb the timing.
You can probably get away with match-marking the hubs before disassembly.
You only have to get the timing within about ±10°, since it's a closed-loop system the adaptation will compensate.
I posted fairly precise measurements around here somewhere that should get you within ±2°.

Shutterspeed and Calichase don't have to worry about these bolts. BMW put the better bolts in after 2006.

[Shutterspeed]

Originally Posted by StickMon

Careful there. The bolts that shear hold the splined sleeve inside the hollow camshaft.
To get to those bolts you have to remove the sprocket hubs.
Once you undo the hubs you disturb the timing.
You can probably get away with match-marking the hubs before disassembly.
You only have to get the timing within about ±10°, since it's a closed-loop system the adaptation will compensate.
I posted fairly precise measurements around here somewhere that should get you within ±2°.

Shutterspeed and Calichase don't have to worry about these bolts. BMW put the better bolts in after 2006.

Thanks for the update on the bolts. Seems I can look into Cali's second point now as a precaution.

[StickMon]

Originally Posted by Shutterspeed

Thanks for the update on the bolts. Seems I can look into Cali's second point now as a precaution.

I went with this over the cryo treated hub or the remachined pump disk.

[dc_wright]

Originally Posted by StickMon

I went with this over the cryo treated hub or the remachined pump disk.

That is an excellent option to go with! IMHO this part has far superior physical properties than the cryo cooled part.
Good to know this option is available!

[inTgr8r]

Originally Posted by StickMon

.......

Shutterspeed and Calichase don't have to worry about these bolts. BMW put the better bolts in after 2006.

A word of caution with this, as there is no clear timeline for when this upgrade was implemented.
Some early '07s still have the old bolts.

[Shutterspeed]

Originally Posted by inTgr8r

A word of caution with this, as there is no clear timeline for when this upgrade was implemented.
Some early '07s still have the old bolts.

Should still be good for me, one of the last 2008's and close to the end of the model run.

[StickMon]

Originally Posted by dc_wright

That is an excellent option to go with! IMHO this part has far superior physical properties than the cryo cooled part.
Good to know this option is available!

I don't know of anybody that's had a failure with the cryo hub or the redrilled pump disk, but I like beef I can see.
If you go with this, I'm pretty sure the pins are a little oversize, so you have to use the stock holes in the pump disk.

Originally Posted by inTgr8r

A word of caution with this, as there is no clear timeline for when this upgrade was implemented.
Some early '07s still have the old bolts.

Thanks. I was thinking they made the change in late '06.