The steel is probably the same. The bolt is missing 1/3 of the threads there is no way it can be rated 10.9.

Bolts are rated on their composition and heat treatment. Nothing about threads.

As an update from Kevin's (@K-MAC) instructions, I cut part of the sub-frame and the bolt as well. I got a shorter nut length and made sure to use the gold-knurled washer on both ends. It was a very tight fit--but definitely possible to do!

Hopefully anyone considering doing this mod will use this as a resource to help guide him/her through.



Couple of key notes:

There is a SPECIFIC way the bushings are installed. You'll notice cut reliefs that are milled down a little bit more on the bush only on one side to help with pressing in the bushes. This also gives specific orientation inside the bushes as the support structure inside is not symmetrical.

The SMALLER bolted-bush goes in the FRONT of the control arm--this one is more "toe" biased than the rear.

Here is the email conversation I had after calling Kevin @K-MAC. Very helpful guy with a great vision for alignment solutions.

I think these bushings are definitely a good way to go about addressing rear inner tire wear and am happy to help support him.



Here is a pic of our email conversation we had--sanitized of course.

Nicely done on getting the workaround figured out and documented for others. :thumbup:

But on this point regarding the bolts and their markings, they are typically marked according to their load bearing capability. This is for obvious reasons of simplicity - the user/designer just has to know what load the bolt will carry safely. This rating will be affected by the composition, heat treatment, geometry, production method, etc.

And at the end of it all, the class 10.9 or 8.8 quantitatively specifies the minimum loads that will cause it to yield (initial plastic deformation) and fail (ultimate tensile stress) under load.

https://www.fastenal.com/en/76/metri...specifications

So I'm actually even more concerned with those parts because it looks like the vendor bought standard Class 8.8 bolts (vs. at least starting with 10.9), and then custom milled them to make their product. So they will not even be up to Class 8.8 any more, forget about 10.9.

In addition to the loss of threads, which could be made up for with a sufficienly long nut, there are the stress concentrations due to the sharp corners, the loss of the strengthening due to grain alignment that happens when you mill through a formed thread, and most clearly, the loss of cross sectional area of the bolt (multiplying ultimate tensile stress by the cross sectional area gives the ultimate tensile strength - the load at which the bolt will fail).

And most bolts have some sort of corrosion resistant coating. If they just milled through them, you've now got bare metal there. I can't tell if they are coated from the photos.

Hopefully BMW's use of class 10.9 was overdone, and you will be safe with those.

EDIT - I see the followup post where the vendor says these have been used for 20 years. That's a little reassuring, but I would not use them.

Not trying to go off on a tangent for this post...but.

Again...classification (for metric) of bolts&nuts are done by material composition and heat treatment. These bolts are still class 8.8 regardless that they were milled, and if anything, it would work-harden them a little--but only on that surface where they were cut and not very deep since any little heat generated wouldn't even have enough time to permeate the medium long enough to form any different crystalline structure to change the mechanical properties, if indeed that is how K-MAC made these eccentric bolts.

That actually might be why K-MAC decided to go with class 8.8 because it's more malleable than 10.9 or higher (aka for machining costs). Then...probably tried to offset the material difference of thread contact with using a 15mm deep nut instead of a standard 12mm for an M12 because part of the thread pattern is compromised and 1/3 missing--or whichever. And then!...to throw another wrench at it--went with an ultra-fine thread-pitch for more clamping force to help accommodate any lack thereof.

But anyway, thank you for your input. I'll def repost to this thread if the bolt fails. But I do not anticipate doing any towing or severe off-roading that would overly stress the suspension components. *fingers crossed*

The kit have been in production for 20 years. Obviously the bolt has been changed from the initial design without regards to installation and maybe capacity. A simple change can be catastrophic, as was seen in the sky bridge collapse of the Hyatt Hotel.

https://en.wikipedia.org/wiki/Hyatt_...lkway_collapse

Great example. Standard reading for anyone who learns or cares about avoiding engineering problems. For the casually interested, the following diagram shows the root cause of this failure that killed so many people. Instead of using a single, long rod as designed, it was decided that two rods of half the length would be equivalent and less difficult to construct.

Can you look at it and see what the design error is?

It was not originally designed that way, but during construction, modifications were made to the design (that they thought would be good enough), signed off on by licensed engineers, etc. Now that we know this was the fault, even then, it may not be clear to some without careful thinking.
Attachment 77516

And if the OP is getting that explanation from the vendor of why it's OK to be milling a weaker bolt and using it as a substitute, then this example is even more relevant here - an in the field modification judged to be good enough even though it contradicts the original design.

Everything I said a few posts up is exactly correct, and much of it is clearly obvious to anyone who may not even be trained in this stuff. Common sense things like that the 10 and 9 in Class 10.9 indicate numeric values for load vs. heat treating (vs. for example 6061T6 aluminum, where the T6 does indicate the heat treating), and that if you mill a chunk out of a bolt, then yes, please trust me on this, you reduce its ability to carry a load. Bare metal will corrode more easily than coated. Formed threads will be stronger than cut threads or milled away threads (replaced by air).

That split rod design caused one of the worst human casualty engineering failures in a hotel atrium where they split the single rod so they didn’t have to thread the nut dozens of feet but then the nut on the bottom of the top level is holding twice the load.

I’ve made a similar engineering goof when not factoring in that a pulley pulls with twice the load!

If you lift 100kg from the ground by pulling down through a pulley, the pulley gets over 200kg of force: 100 from you 100 from the load and any losses.

To the layman, an example of why a little change cause the skybridge to collapse would be if three men were descending down a rope attached to a tow hitch of a 4-ton truck. The rope is rated for 2000 lbs, each man weigh under 200 lbs. If each man grab the rope they can make it, but if the man at the bottom grab the feet of the man in the middle and the man in the middle grab the feet of the man on top, guess what is the weakest link? The man on top since he can't support his weight and the weigh of two other men. The steel rods that supported the sky bridge from ceiling were still in place when the skybridge fell.