Torque setting for front suspension strut to steering knuckle bolts(Z4M E85)

J

jontZ4M

Member
Hi guys

I'm currently re-assembling my entire car after a full refurb. I'm making sure to do everything by the book with correct torques etc etc.

The only thing I can't find is the official torque for the 3no. M12 bolts that connect the front suspension struts to the steering knuckles.

Usually I could work it out from the steel tensile rating on the bolt heads, but these bolts have rusted heads and I can't read them.

Most guides I've found for E46 and E85 show the pinch-type strut arrangements that seem to be more common. My car is the 3 bolt arrangement, not the pinch type. I've failed to find any official data on this arrangement and bolts.

The only thing I've found is this: https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://club.autodoc.co.uk/pdf-manuals/club/bmw/z4-roadster-e85/strut-mount-and-bearing/pdf/EN-how-to-change-front-strut-mount-on-bmw-z4-roadster-e85-replacement-guide.pdf&ved=2ahUKEwjs-bDvob-MAxVHT0EAHQwUGLYQFnoECCEQAQ&usg=AOvVaw1idmjjBgnsghO3vx3mI8HY

^^ but I don't know this guy and have no reason to trust him. He states 107NM. But for an M12 bolt that would mean a 10.8 tensile bolt. If mine turn out to be 8.8 tensile then I'll snap the bolts and be in trouble.

Does anyone have any experience of this?

Also does anyone know if these are red, green or blue threadlock compound? Mine are so old I can't tell.

As I said I don't want to guess/estimate anything, I want it 100% by the book.

Many thanks
 
I'd be using new bolts if I were you. If they are so rusted you cannot see the markings how do you know if they will hold up? Can't say I've ever seen a three bolt knuckle on a Z4 though.
 
These are 10.9 bolts, and the two smaller bolts come with encapsulated red threadlock on them. The longer bolt does not use threadlock.

***this may be wrong, see the post from TomK below***Factory torque is indeed 107nm, this is confirmed in this thread: https://www.bimmerforums.com/forum/showthread.php?2456202-Shock-and-Strut-torque-specs-for-M-Roadster (note that "By the book" means replacing the bolts)

@Rockhopper: Z4Ms use a three bolt knuckle like the E36 and Z3
 
TomK said:
TIS states 81NM for these bolts on the E86 platform
Click to expand...

I am not 100% sure on this. I suspect that this is only referring to the pinch bolts used on the non-M E85 and E86. The three bolts used on the Z4M are M12x20 and M12x42, the part numbers for the bolts (though not the knuckle) are the same between the Z4M and the E36.

I would be very surprised if the torque specs are different, and just happen to be the same as for the pinch bolt.
 
Wow what a minefield!

- yup I see now that the two 20mm long bolts need replacing.

- looking at the data table I also read it as 107NM, although as usual, clear as mud.

- so do we mean that the new 20mm bolts come from factory with the microencapsulating compound already on them? I've never seen this with cars I've dealt with, or at least not that I've known about. Do we think that's the reason for these and some of the other bolts on the car requiring replacement after removal?

How exciting.
 
^^ I just had a closer look at the various bolts that need replacing throughout the car. They all seem to be self-locking bolts with differing locking mechanisms. The 20mm strut bolts are thread lockers. The front brace and lollipops are "place lock" heads or washers. Not sure what rear brace bolts are but they'll be some sort of lock. So that answers my question from above I guess.
 
In case it helps others, this is the list of bolts that need replacing and sourcing for the Z4M E85 underside refurb:

Please let me know if you think I've missed anything.
 
jontZ4M said:
In case it helps others, this is the list of bolts that need replacing and sourcing for the Z4M E85 underside refurb:

Please let me know if you think I've missed anything.
Click to expand...
At the risk of being wrong again :roll: I'm fairly certain the torque speculation for the half shaft bolts is 100nm not 80.
20250409_130856.jpg
 
^^ great timing, that's now the only figure that I'm still trying to nail down. I've seen 65-100nm from various sources. My only concern with the 100nm figure is that it is way above the max figure of 66nm for M10 10.9g bolts claimed on the general BMW bolt sheet. I can't link anything until I get home to show.
 
These are higher because they are effectively stretch bolts, they get torqued past the yield point for more clamping force. This is why they (and all the torque + angle bolts) have to be replaced every time.
 
jontZ4M said:
^^ great timing, that's now the only figure that I'm still trying to nail down. I've seen 65-100nm from various sources. My only concern with the 100nm figure is that it is way above the max figure of 66nm for M10 10.9g bolts claimed on the general BMW bolt sheet. I can't link anything until I get home to show.
Click to expand...
I did mine a few months ago to 100, has been fine. I do trust TIS in this instance as there isn't the vagueness in model designation. All S50/52/54 variants are specced the same,
 
OK thanks guys that all makes sense. I've ordered all required bolts(except driveshaft) from BMW and will collect on Sat. Will call forum member Wassup now to source the driveshaft bolts from him and then that's all of the required bolts replaced. Thanks for all your help so far. Has been a fun learning experience.
 
ed80 said:
These are higher because they are effectively stretch bolts, they get torqued past the yield point for more clamping force. This is why they (and all the torque + angle bolts) have to be replaced every time.
Click to expand...

Just a small thing registered there: you mentioned that all torque + angle bolts get replaced, BUT the rear diff->subframe bolts are torque + angle but they are not supposed to be replaced as far as I can tell?
 
Ah, I think you are right. I wonder if this is because they are compressing the diff bushes rather than just a steel on steel bolted connection?
 
Hi guys, agreed it's bit of a minefield, the E14 torx differential bolts are reusable, even with a 20nm jointing torque plus 90 degree angle.

I was advised by a BMW master tech to go to 80nm on the M10 driveshaft to differential bolts as I tried to research this and couldn't get a definitive answer. Most stretch bolts have a torque rating plus angle, for stretch, but these don't.

Anyway, I've been running 80nm for about 10 years on these e torx bolts and not had any issues, even after removal and refitting them a few times. Even getting to 80nm on an M10 bolt feels uncomfortable :o
 
Wassup said:
I was advised by a BMW master tech to go to 80nm on the M10 driveshaft to differential bolts as I tried to research this and couldn't get a definitive answer. Most stretch bolts have a torque rating plus angle, for stretch, but these don't.

Anyway, I've been running 80nm for about 10 years on these e torx bolts and not had any issues, even after removal and refitting them a few times. Even getting to 80nm on an M10 bolt feels uncomfortable :o
Click to expand...

That was exactly my feeling also. 100nm just feels wrong to me, but I understand the concept. It's not super important for this build anyway as I plan to remove and re-do the diff completely at some point as I think I can do it better. So will be re-tightening again then anyway.
 
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