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  #61  
Old 05-18-2017, 11:26 AM
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Quote:
Originally Posted by dannyzabolotny View Post
I've removed the plate once and re-used the bolts, and most recently I removed the plate againó I plan to re-use the bolts again. I don't care what BMW says, these are regular bolts and will likely outlive the X5.
When you torque reused bolts what target do you use? Do you still got to 42 ft lbs + 90 degree angle?
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  #62  
Old 05-18-2017, 12:11 PM
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The reinforcement plate is an integral part of the suspension and is there for performance and safety.

The bolt torquing sequence in the manual is that of TTY bolts. TTY bolts should not be reused as the torquing sequence takes them to the point they begin to stretch. While they may reach torque specs when re-used they will be stretched further, causing the bolt to weaken and reducing the clamping capability.

Reading posts of many threads here and in other forums, I see pricing of the bolts driving the question of re-use, individuals having no problem with re-using the bolts posting that as verification that it is fine to re-use the bolts and folks that do not have the appropriate education to state it is not necessary to replace the bolts.

The Bentley BMW service manual clearly states that the bolts are one time use only. There is also a warning statement.

I've been tempted to re-use the bolts because of the cost but I always think of a time on the Dallas Tollway when there was an accident in front of me and I had to jerk the wheel and fly across three lanes at near 80mph. I expected I would slide into the outside barrier but I corrected and all was well. The hit would have been on my wife's side. I don't know if re-used bolts would have broken and the suspension collapsed but---

My only point is the price of the bolts is small in comparison to injuring myself, certainly a member of my family or people in other vehicles. I don't expect this will change anything. I think those seeking justification for not re-using the bolts to avoid the cost are the ones wearing blinders. At least don't let the cost be your reason for re-using them.

I think the prudent course of this discussion should be to find a source for the exact bolt from OEM or some other manufacturing source to lower the cost and end the debate.
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  #63  
Old 05-18-2017, 12:34 PM
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^It's not much of a debate. Either you are okay reusing them (as MANY have), or you are not. Neither side has proof of any negative effects, other than one poster who encountered noise from the chassis, of reusing the bolts. BMW most likely recommends replacement simply because they are a part of the vehicle's structure. Much the same as them recommending replacement of all the nuts on the suspension whenever a component is replaced. Seen people reuse those too, though I do replace those as they usually come with the suspension component.

I reused, and will continue to reuse them until such time the reinforcement plate starts squeaking as some have reported, or the bolts show some visible sign of wear.

Quote:
Originally Posted by blktoptrvl View Post
When you torque reused bolts what target do you use? Do you still got to 42 ft lbs + 90 degree angle?
I got 42ft lbs and then did an ~75 degree angle. I used red locktite on the bolts as well just as a precaution.
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  #64  
Old 05-18-2017, 01:01 PM
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I just torque em good and tight. It's just a stiffening plate, not some critical control arm.

And yeah, the cost of the bolts is the main concern for me— I don't feel like spending a bunch of money on something so non-essential, especially when the X5 (and my 540it) need other, more expensive parts. I just had to spend $160 on a new key for my 540it and like $700 to fix my X5's transfer case and front driveshaft. It's all about priorities, I guess. If the X5 was my only car then maybe I'd consider buying new bolts, but since I have several other cars, I gotta cut corners somewhere.
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  #65  
Old 05-18-2017, 02:27 PM
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I am not trying to convince anyone they are making a mistake and I don't care about anyone's choice. I do think it important those asking are provided information to make an informed decision. When I learned the cost and wondered why I found information like the following two: Proper installation and use of T-T-Y Bolts - Fel-Pro Only Torque to Yield Bolts I didn't find anything in print that it doesn't matter or it is a myth. IMO opinion it is not about proof they have failed it is about the reason they can fail. Granted MANY re-use the bolts. At one time MANY believed the Earth was flat.

It is most certainly is a debate, as both sides always 'pitch' what they do and why. What gets posted in other forums are the same debate and also anecdotal and not statistically applicable.

Reused bolts can reach the torque spec. It is not about achieving torque spec it is about the lose of clamping power and a weakened fastener. BMW uses single use fasteners in places such at when the bolt threads into aluminum. What suspension fasteners does BMW state- DO NOT RE-USE?

Those considering re-use should be provided the opportunity to make a decision based on the worth of the science rather than conjecture.

Again, I couldn't care less what anyone does but I assume at least some that are re-using the bolts have not been exposed to the technical data.
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  #66  
Old 05-18-2017, 05:20 PM
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Quote:
Originally Posted by blktoptrvl View Post
When you torque reused bolts what target do you use? Do you still got to 42 ft lbs + 90 degree angle?
----------
Disclaimer - don't try this at home.
----------

No, you can't do that. That procedure, if repeated enough times, will almost certainly break the bolt.

The Y = "yield" in TTY suggests that when installed the first time, if done properly with careful surface preparation, light oil on the threads and washer (or whatever exactly is specified for this application), the stress on the bolt will exceed the yield stress, resulting in plastic deformation (yield, permanent stretch).

My Bentley, page 310-2, says the spec is 56 Nm (41 ft-lb) + 90*. In addition to saying the fasteners should be new, it says the tightening should be done with the car on the ground and loaded, bouncing the suspension a few times before final tightening. So for those purists who want to follow specs to the letter, there it is. I can't imagine a professional mechanic getting on the ground to do this, just like (I hear) they don't actually use new bolts, and (I hear) dealers don't even stock them.

My Bentley, page 020-4, referencing DIN 267, give a general torque value for M10 10.9 as 66 Nm. They intend that as a default, safe value for bolts with otherwise unspecified torque values. So if you were to tighten just by torque value (and no angle spec), using 66 Nm should be possible without plastically deforming the bolt. And a little more should be possible on re-use, due to the work hardening.

The plastic deformation "work hardens" the bolt, meaning that its elastic range has now been extended to include the plastic strain.

So when you apply 56 Nm, and then add 90 degrees, at some point in that 90 degrees, the bolt "should" begin plastic deformation. You might feel this as a fairly sudden change where pulling further on the wrench is not actually getting much more difficult. Once done with the 90 degrees, the bolt (and maybe nut too, since these are not TTY bolts, they are just regular bolts used in a TTY application) will have plastically deformed, imparting a permanent stretch to the bolt (and maybe deforming threads too).

Ideally, when re-using these, you should theoretically be able to tighten it back up to this exact bolt stretch multiple times with no problem at all. And all this would be in the elastic region, with no further plastic deformation. The bolt would be performing exactly as intended.

So that is the goal = tighten it up with the exact same stretch, or "strain" to use the proper term. Not easy to do. And certainly less easy than telling other people to just use new ones.

Following the same 56 Nm + 90* will definitely not do this, since the 90* will be pushing further into the plastic region each time it is done, until finally the ultimate tensile stress is reached and the bolt will snap.

If you knew the torque applied the first time, when you did the 56 Nm + 90*, perhaps 70 Nm, you could apply that pretty safely. Maybe back off a little.

If you feel plastic deformation (when angle increases without a linear increase in torque required), you've gone too far, so stop. So this is what I do, torque to the torque value, but ready to feel for plastic deformation and stop.

If you want to follow the instructions, but modify them, as crystalworks suggested, with 75* rather than 90*, I'll say something like that makes sense, but I don't know if the answer is 75* or 30*. This would be TTA rather than TTY, and should be the most reliable way to do it, if you knew the correct angle.

To answer that experimentally, you could start with a new bolt, install with the spec of 56 Nm + 90*, and measure the actual torque when you reach 90*. (Ideally there would be some time spent here to let things settle out). Then back off to a low torque value, torque to 56 Nm, and measure the angle required to get back to the final torque you just measured. In theory, with no change in surface conditions, that angle should be repeatable. But it's not perfectly repeatable, so at this point, it is easier/safer/more profitable to say replace them.

It would be great if someone some day would do this experiment with a new bolt.

Also, if any of the purists who use these things only once would like to send me their old throw-aways, I'd be happy to test and post any findings.
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  #67  
Old 05-18-2017, 05:55 PM
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Is there any way to test a new bolt and then locate a bolt that is the same but is not so expensive that could be recommended whenever this issues pops up?
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  #68  
Old 05-18-2017, 05:57 PM
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Quote:
Originally Posted by bcredliner View Post
Those considering re-use should be provided the opportunity to make a decision based on the worth of the science rather than conjecture.

Again, I couldn't care less what anyone does but I assume at least some that are re-using the bolts have not been exposed to the technical data.
There is no science or technical data provided by either side of the "debate." BMW does not provide any either, publicly anyway. Anecdotal is the strongest "science" being provided at the moment. blktoptrvl chimed in with input from mechanical/civil engineers as well in regards to the properties of the bolts themselves. Earth was flat point was reductio ad absurdum to say the least. Pythagoras theorizing the earth was spherical is far removed from having any relation to these bolts.

The only other personal experience I can provide is that none of the techs at the shop I was at would replace those bolts, or torque them with the suspension loaded.

The nuts on tie rod ends, ball joints, etc are all recommended to be single use.
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  #69  
Old 05-18-2017, 06:45 PM
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What is the thread pitch?

I think I will just go ahead and order 4 (cheap) M10x60s Because I know at least two will have enough clearance. And then order two (Grade 10.9 M10x55 BMW) If I can't find the same from a non OEM source.

I'll put them on the shelf just in case. And next time I drop the place see if the sixties will fit in all locations.
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  #70  
Old 05-18-2017, 07:40 PM
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The flat earth reference is not an RAA but it is suggesting what has been attributed to Pythagoras's conclusion the earth is round was a scientific conclusion that was ignored due to so much anecdotal views to the contrary.

It is very simply flawed to make a conclusion from personal experience, especially with this small of a sample. Opinions, anecdotal input have absolutely no connection to science or technical substantiation.

There is no reference in the service manual recommending replacement of suspension hardware. I have seen that recommendation from aftermarket vendors. But as you said it is a recommendation. That is not the same as DO NOT REUSE.

As far as some technical support to not reuse the bolts see posts 65 and 66. I have an open mind to consider any supporting scientific data you can provide. Otherwise, your rationale for using the bolts again is flawed, so it is clear, flat wrong. More of the same will not change that.
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