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Old 03-20-2020, 08:21 AM
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upallnight upallnight is offline
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Originally Posted by oldskewel View Post
Nicely done on getting the workaround figured out and documented for others.

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.

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.
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.
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