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#21
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You misunderstood me. I was saying that you prob wouldn't reach yield until about 160 N·m where 122 is spec. (that could be off a fair amount it might not be a direct ratio). Reality check; M10 10.9 spec is 66 N·m and ratio to yield: 88 N·m. In testing, it was right about 90 N·m where the bolt went to plastic and the torque stopped climbing. BTW: a very very weird experience to turn a bolt 45° and no change in torque! So: a 12mm should handle 140-150 N·m before damage. You should be able to torque to 122 limitless times. So back my original stance: no problem at all to reuse, i would throw on thread lock if I had handy but wouldn't go out of my way if I didn't.
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2011 E70 • N55 (me) 2012 E70 • N63 (wife) |
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#22
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As a matter of curiosity, how did you arrive at 88 N.m as the torque at yield. Shouldn't we consider Proof load rather than yield. Proof load for 10.9 steel is 830 MPa. Effective tensile area (at the root of the thread) is about 50 mm2. So 830 x 50 is 41500 N (41.5 KN Clamping Force) Similarly for M12, it works out to be about 53 KN. Anything above this will cause permanent deformation. So we're at the limit already. Agree? |
#23
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You can definitely safely reuse those bolts if you don't see any signs of degradation.
Attached is a BMW spec on bolt torques, since you seem to be interested in drilling deeper into this than most. BMW bolt torque specs detailed.pdf Some complicating factors, just to point out how the mechanics / physics / metallurgy is not as simple as one might like (and why the "class 10.9", etc. exists to try to remove these complications from things people need to worry about every day):
If you're looking for more information and flames in a related topic, search on here for advice on whether to re-use the stiffener plate bolts (the 6-bolt aluminum or steel plate under the engine).
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2001 X5 3.0i, 203k miles, AT, owned since 2014 |
#24
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#25
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An additional thing you can do to give yourself confidence that no plastic deformation has occurred is to see if you can easily thread things together with your fingers. Plastic deformation will be uneven, making that impossible over a long depth.
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2001 X5 3.0i, 203k miles, AT, owned since 2014 |
#26
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"but re-using would surely logically depend on corrosion, age, mileage, etc. as well, but that is not given here" and my high mileage and age of the car |
#27
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good catch I used tensile vs. yield. The correct number would be 122*94/78=147 N·m for yield. (20% higher than proof). The proof strength is 0.83 of yield not 0.75.
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2011 E70 • N55 (me) 2012 E70 • N63 (wife) |
#28
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That's a very good test. Especially when you can use a new nut on an old bolt. Suspension bolts are usually on the order of 2x safety factor. A 12mm bolt has a clamping force of 5T. Two means 10T. Just shy of 8T@ sheer force each so the brake caliper can withstand 16T of sheer force that is a lot more than the tire can apply in perfect conditions.
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2011 E70 • N55 (me) 2012 E70 • N63 (wife) |
#29
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https://www.bmwoffairfax.com/order-parts-online.htm
Just reuse the bolts as the next brake job will be end of life.
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2005 X5 4.8IS The Blue ones are always FASTER.... Current Garage: 2005 X5 4.8is 2002 M5 TiSilver 2003 525iT 1998 528i Former Garage Stable Highlights 2004 325XiT Sport 1973 De Tomaso Pantera, L Model 1970 Dodge Challenger T/A 4 sp Alpine White 1970 Dodge Challenger T/A 4 sp GoManGo Green 1971 Dart Sport, “Dart Light” package 1969 Road Runner 383 1968 Ply Barracuda 340S FB Sea-foam Green |
#30
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Yes, replace them. That's the answer you want to hear, right?
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