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Old 01-10-2019, 04:07 PM
oldskewel oldskewel is offline
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Originally Posted by mr_robot View Post
OEM uses M10x55, wonder if these would work, available in Chromoly and SS.

I believe you need 6 of them:
Yes, there are 6. Consider new nuts too if getting new bolts. Stainless steel would typically not have the required strength that the OE Class 10.9 have. I re-use mine, carefully.

Those look good. If I were to replace mine, I'd prefer those over the BMW $$$ ones, even if as a matter of principle vs. BMW marketing.

Here are the specs on the BMW bolts, so you can see exactly how they differ:
Threads, rating: M10 - 1.5 x 55mm, class 10.9.
bolts: 16mm hex head with captive flat washer. BMW PN: 31101096987
nuts: 16mm hex nut with flange. BMW PN: 33306760587

First thing to know is that even the magic BMW ones are regular high strength bolts. Not blessed by the Pope or anything. Not specially made for the stiffening plate. They are just bolts and nuts as specified above there.

I see those ARP ones are 5mm longer. Should not be a problem, especially if you add a washer to make up for the fact that the ARP ones don't have one.

The ARP ones don't specify Class 10.9, which I consider weird. Class 10.9 means something, and 10.9 will be on the head of the bolt and on the face of the nut. The torque value they specify does suggest it would be strong enough. Maybe they are Class 10.9, and it is marked on the bolts, but ARP does not advertise it, which like I say seems weird.

ARP specifies 73.2 Nm as the torque value
Bentley manual, p.020-4 says for a Class 10.9 M10, torque to 66 Nm
The stiffening plate bolts (those bolts for that application) say 56 Nm + 90*

The torque spec for this application relies on some yield, and if you do have a Class 10.9 bolt, the plastic deformation / work hardening can be assumed to be as the design engineers intended. But if you now use a stronger bolt (torque spec on these ARPs is 10% higher ; and the torque spec is typically chosen based on yield = when plastic deformation begins), going to 56 Nm and then doing the 90* beyond that will give a different result.

So I think a regular Class 10.9 bolt would be better for this application - yes those should be easy to get. No doubts about anything if getting non-BMW bolts that meet the above spec.

And if using the ARP ones, I would torque to the 73 Nm bolt spec and no further, and expect that to be just fine. And that is similar to what I do when re-using my BMW bolts - I torque to 66 Nm, without doing the extra angle.
2001 X5 3.0i, 190k miles, AT, owned since 2014

Last edited by oldskewel; 01-10-2019 at 05:03 PM.
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