Originally Posted by oldskewel (Post 1129436)

I don't know why they do what they do. But I do know ...

If the torque procedure does actually cause plastic deformation ("yield"), then that procedure (e.g., removal and reinstallation) cannot be performed indefinitely. Each time you'd re-install with a little more plastic deformation, you'd be moving closer and closer to the ultimate tensile stress ==> fracture.

So if re-using, and yield may have occurred previously, you can't blindly do the torque + angle installation procedure. You need to be a little smarter and more careful. Knowing that might be beyond the ability of many professionals and DIYers, that could be why BMW decided it's pretty easy to just say re-use them.

BTW, other stuff that might be safety related, and is easy for BMW to say (from the owner's manual):

"For your own safety, use genuine parts and accessories approved by BMW."

"Installation and operation of non-BMW approved accessories such as alarms, radios, amplifiers, radar detectors, wheels, suspension components, brake dust shields, telephones (including operation of any portable cellular phone from within the vehicle without using an externally mounted antenna) or transceiver equipment (for instance, CBs, walkie-talkie, ham radio or similar accessories) may cause extensive damage to the vehicle, compromise its safety, interfere with the vehicle's electrical system or affect the validity of the BMW Limited Warranty. See your BMW center for additional information."

"For your own safety: use only brake pads that BMW has released for your particular vehicle model. BMW cannot evaluate nonapproved brake pads to determine if they are suited for use, and therefore cannot ensure the operating safety of the vehicle if they are installed."

Similar thing on BMW-only wheels.

Snow chains only on the 17" wheels.

"In order to ensure the safety and reliability of the brake system, have the brake fluid changed every two years by a BMW center"

I'm sure that's all fair advice, and for some people, they'd be better off following blindly rather than thinking. But it also shows that BMW will say things in the name of safety that may be overly conservative for people who know a thing or two.

Originally Posted by bcredliner (Post 1129441)

BMW states NOT to re-use the bolts. That's the reason I asked how you know the reason BMW makes the statement is because they will loosen. How do I
know when I've reused them too many times? Could the second time be too many? I agree BMW is conservative and some statements are liability
based.

Originally Posted by oldskewel (Post 1129465)

Well, I think you asked lincoln, and I answered. I'm not sure about BMW's reason, and don't know if he is.

If the bolts + nuts deform, it may be detectable by seeing how easily they thread back together before reassembly. So if they thread back together easily along the full length of the bolt with finger torque, there is little or no plastic deformation, and I would re-use them as if they were new. (full torque + angle)

If they don't thread easily, they are deformed.

If you were able to re-install them to the exact same strain (the same full stretch they had before, but no more, which would be more plastic deformation), you could do it almost indefinitely. But you cannot just blindly follow the Torque plus (same) Angle repeatedly. It very well could be that due to tolerances and bad luck, it would fracture on the first re-installation.


Or it could be that if things are done carefully and things are in spec, the bolts go right up to the yield stress, but no further. In that case, with no yield, you should be able to reuse indefinitely.

Experiments could get a better answer on this - it depends on the bolts as well as the things that are being clamped (the stiffening plate, washer, tube, etc.).

But if you re-install with no extra plastic deformation, you will get all the clamping force, and no inching closer to fracture.

Do you know the feeling when you're torquing a bolt and can feel the threads strip? Like the torque is increasing linearly with increasing angle, and then when they strip, it's like the angle increases without any increase in torque (or in the case of threads, it would be a reduction in torque as the threads break away)? That's an indication of yield (plastic deformation), and is exactly the feeling when the whole bolt deforms in a TTY scenario. If you pay attention while torquing, you can try to feel and hopefully not detect any of this. If you don't plastically deform it any more, then you'll still be in the elastic region which was extended due to work hardening.

I know some applications will call for things like a pulley bolt to be replaced upon replacement of the pulley, even if it seems fine. I see that as a different story, and would replace it if they say so. One main difference there is that there is a single point of failure. These stiffening plates have 6 bolts, so if one or more breaks, it will not be catastrophic like a pulley bolt failure would be. And will not require an engine teardown like a TTY head bolt would.

Originally Posted by lincolnshibuya (Post 1129474)

it's just saying that you believe on lifetime fluids because BMW told you so..

Originally Posted by bcredliner (Post 1129513)

That wasn't nice. You have no idea what I do, my experience or knowledge.

You claimed the solution is Loctite so they don't come loose. I just asked how you know the issue is about the bolts coming loose. Do you know?

Originally Posted by lincolnshibuya (Post 1129525)

I apologize, don't want to be rude... that wasn't directed at you.. just in general :)

the service manual needs to state that for liability purposes in case they get sued for faulty instructions, it's the same stuff on youtube where they put a warning message that it's only for entertainment purposes... TTY bolts are typically things a DIY need to look out and in most cases without a service manual handy it will just be tighten as in tight.. of course if there are issues with tightening it then it's your own decision.

take for example the transmission pan bolts.. if the service manual says not to re-use it since they are aluminum and TTY then you'll probably go to the cautionary side of buying new one since the end result might be catastrophic... now compared that to the stiffening plate.. will your engine drop along the highway?

I have done lots of maintenance on my mountaineer and pretty much the suspension parts were all re-used (even the axle nut) the service manual says to discard all of them.. it still runs and I'm still alive.. if I got involved in an accident because the wheels fall off will I sue ford?

Originally Posted by cn90 (Post 1129555)

- For this particular issue, ignore BMW statement.
- Re-use the bolts and move on.

Originally Posted by bcredliner (Post 1129580)

Great! So if anything bad happens you accept the liability?