Stiffening plate removal / reinstallation

[cn90]

Originally Posted by bcredliner

Why does BMW state not to reuse the bolts and what can happen if they are reused?

You can ask BMW.

Personally, I think BMW has its strength and weakness.

- Strength is in esthetic "curb appeal", driveability, the "name BMW" etc.

- Weakness is: reliability and repair procedure is overly cumbersome.
Technical manuals were written with liability in mind. This bolt discussion is somewhat dumb simply b/c the crazy (paranoid) engineers wrote that sentence of "replacing the bolts" and not-too-smart people follow it like the Bible. Remember "it takes 2 to tango" and I am not part of this tango.

[upallnight]

Originally Posted by cn90

You can ask BMW.

Personally, I think BMW has its strength and weakness.

- Strength is in esthetic "curb appeal", driveability, the "name BMW" etc.

- Weakness is: reliability and repair procedure is overly cumbersome.
Technical manuals were written with liability in mind. This bolt discussion is somewhat dumb simply b/c the crazy (paranoid) engineers wrote that sentence of "replacing the bolts" and not-too-smart people follow it like the Bible. Remember "it takes 2 to tango" and I am not part of this tango.

Same reason why BMW tells owners that the ATF is lifetime, but if you go on ZF's website they state that ATF should be changed every 40,000 miles, not unless it is revised by the car manufacturer. So who are you to believe, the company that sells the trans to the manufacturer or the manufacturer that buys the trans and install it in the car.

[bcredliner]

Originally Posted by cn90

You can ask BMW.

Personally, I think BMW has its strength and weakness.

- Strength is in esthetic "curb appeal", driveability, the "name BMW" etc.

- Weakness is: reliability and repair procedure is overly cumbersome.
Technical manuals were written with liability in mind. This bolt discussion is somewhat dumb simply b/c the crazy (paranoid) engineers wrote that sentence of "replacing the bolts" and not-too-smart people follow it like the Bible. Remember "it takes 2 to tango" and I am not part of this tango.

Insulting others reflects on ones own character.

It is not what anyone's opinion is, the question that needs to be answered is why does BMW states not to use the bolts and what happens if you do. You think it is paranoid engineers and nothing happens. But that is an assumption without any basis in fact so you really don't know. It's just that simple.

[andrewwynn]

Because they set themselves up for liability. By err on the side of caution they can't be responsible for anybody using anything outside their specs.

The simple math shows that the corners are held with about 20,000# force in the back and 10,000# in the front. It wouldn't surprise to discover that is just enough or to find out it's 4x as much as needed.

BMW guys must see the threads asking and choose not to answer with authority on the matter. It feels like only the guy that designed it knows why and chose not to divulge why so now the only reason anybody does it is "because somebody said so". Since childhood that is not an acceptable answer for thinking people so it drives thinking people crazy when the reason is not given.

I've seen nothing of authority on the subject. (only the generic torque spec sheet with what but not why).

I have driven the X5 without the plate and can absolutely feel the difference in the front end so It definitely does it's job. I can also say that with much smaller bolts it firmed right up so for the majority of the function it does not need nearly the spec clamping force. (I will measure the current torque/clamp force on my plate now to get a sense of what might actually be required).

I will not be too surprised to see that my plate has signs of sideways slip but it won't surprise me if there isn't either. There is a good amount of surface area clamped together so there is likely some force multiplication e.g. with 7500# clamp force it might take 12000# to move it sideways.

When you hit a big bump on one wheel it could easily generate forces on that scale and I'm sure that went into the why In the original design.

Unless someone beats me to it I will be getting some very useful data that can be used to decide which route to take.

The "easy way out" is to assume BMW is infallible and follow them blindly. That solution will have you paying $920 for replacing the four door lock motors (parts only) vs $24 for the actual motors.

If there was even one single paragraph with authority explaining the why, it could end the debate.

There are people that recommend leaving the plate off. Terrible idea, the other extreme is to always replace the bolts. The most logical solution I guarantee is in the middle. And I diagree that it's all about cost: if the bolts were an appropriate $2 each I would still want to replace only if it's logical to do so: we don't replace our bolts each use but nobody worth their weight in cheese will reuse a head bolt that is just moronic.

I contend that it's not much smarter to replace a bolt "just Because" if it works out that the bolt has no wear from normal use. It's much smarter to get some informed data and proceed on a logical path.

If the 56+90° ends up taking 120 N·m and is well into plastic deformation I would not reuse that bolt. I would probably get a new bolt and pay attention while installing and stay in the non deformation zone as long as I can back it up with some math.

Eg if the spec is 7500# clamp force but you can achieve 7000# without distortion you can believe that is what I would do (or switch to fine pitch bolt etc).

This story will continue. Withing a couple weeks I will be doing some measurements that will give us some actual values not striaght up guess work.

[andrewwynn]

I will take a new bolt and TTA while measuring the torque applied to get a decent estimate of clamp force. From that I can reverse engineer what straight torque can get a similar clamp force without going into plastic deformation.

If not possible with the stock bolts I will be swapping out the bolts to a size that will achieve the factory design of clamp force without damaging the bolt.

One other thing to consider: the back corners have a PAIR of bolts to hold the sway bar. I would be comfortable with reengineering to have the back bolts backed down to normal torque since that will net 15,000# clamp force and double the surface area on the plate.

This may have just gotten stupid simple. Class 12.9 bolts have a higher yield strength than the tensile strength of the 10.9 bolts. You can buy FIFTY of them for less than the SIX if you buy an official BMW bolt.

I'll be doing some measurements and if simply upgrading to class 12.9 will achieve the same clamp force without going to a bigger size you can bet a dozen donuts that I will have a dozen of them in short order.

The only conceivable risk is they could be brittle enough to break vs stretch more but two things about that : whatever maneuver could cause that, a corner of my restriction plate coming loose will be the least of my worries and it will be nowhere near the clamping force maximum I'm betting.

There are also grade 14.9 which are far above and not expensive "each" but the smallest order I found in a quick search is for 1000 quantity.

So: I'm quickly leaning toward get a beefier bolt so I cab achieve the same clamp force of the design spec but not cause any wear on the bolt. With any luck I'll discover that the TTA causes no plastic deformation and I'll be able to report a torque value that approximates the TTA without hitting deformation. I myself would have no problem torquing to 80 N·m vs 90 N·m if the former caused no damage and the latter meant single use on $60 of bolts.

To be continued.

[andrewwynn]

Also somewhere in the middle. If the bolt is plastic deformed from the initial install, it will have a smaller cross section and the next time it's installed using the same procedure it will logically have a lower clamp force that's the entire explanation for single use.

That said it might be higher than proof load but be less than yield so there is no deformation but it's stressed past proof load so NASA can't reuse the bolt, but DIY on BMW yes sure.

Back to the original thought: people are ONLY GUESSING because nobody took the time to take a friggin bolt or two and measure what happens.

It will be laughable if the TTA ends up being less than the normal spec of how much torque to apply to a 10mm bolt.

The debate isn't pointless it preps the mind and mindset for doing some appropriate texts/experiments that can finally answer the question.

If for example TTA process ends up at 65 N·m than BMW are aholes to tell people to replace a bolt that wasn't even pushed to proof.

If the bolt ends up BENT due to sideways loading, that could be another good reason to switch out the bolt.

One way or another I will using a reusable solution in the future. The results of my tests will be shared so finally people can have measured values to use as well to make an educated determination rather than take one of the extreme sides must replace "because it says" or it can't really need it (with absolutely NOTHING to back that up).

My 3/8 bolt (5500# clamp force) for months holding my plate on will be solid proof one way or the other. If there is no side slip evidence on my plate it's absolutely proof positive the M10 torqued past proof is waaaaay more than needed

If the plate has a oval hole worn in because I'm a moron that will be solid evidence that it needs closer to design spec. I'm kinda hoping that there will be clear evidence of motion of the plate. I drive over curbs a lot. If I didn't ditch witch my car into slipping the plate nobody else will.

I've been wanting to follow through with this test ever since I put the temporary 3/8 bolts in. (I didn't want to put the original bolts through more stress since I took them in and out a few times in a week (removed plate to clean engine, put back bolts in to hold sway bar, removed those to reinstall plate, removed again to take plate out to install new oil absorber aka sound insulation then install once more).

I was being lazy the last time when I should have found the original bolts but just reused the ones I had under the car with me.

[bcredliner]

Originally Posted by andrewwynn

Also somewhere in the middle. If the bolt is plastic deformed from the initial install, it will have a smaller cross section and the next time it's installed using the same procedure it will logically have a lower clamp force that's the entire explanation for single use.

That said it might be higher than proof load but be less than yield so there is no deformation but it's stressed past proof load so NASA can't reuse the bolt, but DIY on BMW yes sure.

Back to the original thought: people are ONLY GUESSING because nobody took the time to take a friggin bolt or two and measure what happens.

It will be laughable if the TTA ends up being less than the normal spec of how much torque to apply to a 10mm bolt.

The debate isn't pointless it preps the mind and mindset for doing some appropriate texts/experiments that can finally answer the question.

If for example TTA process ends up at 65 N·m than BMW are aholes to tell people to replace a bolt that wasn't even pushed to proof.

If the bolt ends up BENT due to sideways loading, that could be another good reason to switch out the bolt.

One way or another I will using a reusable solution in the future. The results of my tests will be shared so finally people can have measured values to use as well to make an educated determination rather than take one of the extreme sides must replace "because it says" or it can't really need it (with absolutely NOTHING to back that up).

My 3/8 bolt (5500# clamp force) for months holding my plate on will be solid proof one way or the other. If there is no side slip evidence on my plate it's absolutely proof positive the M10 torqued past proof is waaaaay more than needed

If the plate has a oval hole worn in because I'm a moron that will be solid evidence that it needs closer to design spec. I'm kinda hoping that there will be clear evidence of motion of the plate. I drive over curbs a lot. If I didn't ditch witch my car into slipping the plate nobody else will.

I've been wanting to follow through with this test ever since I put the temporary 3/8 bolts in. (I didn't want to put the original bolts through more stress since I took them in and out a few times in a week (removed plate to clean engine, put back bolts in to hold sway bar, removed those to reinstall plate, removed again to take plate out to install new oil absorber aka sound insulation then install once more).

I was being lazy the last time when I should have found the original bolts but just reused the ones I had under the car with me.

See paragraph one. https://www.fastenal.com/en/77/reuse-of-fasteners

[X5only]

Originally Posted by bcredliner

See paragraph one. https://www.fastenal.com/en/77/reuse-of-fasteners

Well done Bcredliner, that article should surely kill this thread. And to add flowers to the grave, here's one thing. Cost to me for 6 new BMW bolts $4 (which is the return shipping for the old, rusty 6 bolts).

[bcredliner]

Originally Posted by X5only

Well done Bcredliner, that article should surely kill this thread. And to add flowers to the grave, here's one thing. Cost to me for 6 new BMW bolts $4 (which is the return shipping for the old, rusty 6 bolts).

I really appreciate your post. Thank you.

[andrewwynn]

Originally Posted by bcredliner

See paragraph one. https://www.fastenal.com/en/77/reuse-of-fasteners

I read the whole article. Very good read. I was saying the same thing regarding if it's ok to reuse a bolt. All my "it is ok" math is based on don't exceed proof load.

I did my first exam of an old bolt today but since I don't have the "before" nothing conclusive yet, but preliminary measurements suggest the bolts are actually strained past proof, and would have a cycle lifespan like the above article explains. (Eg ok to use 5 times).

I've only measured the bolt after use and I measured a slightly lower than expected thread pitch.


Over the first 9mm the threads seem to line up on a 2/3 thread per mm or 1.5mm/thread as expected.



But at 36mm (24 threads), it's clearly about 36.2 mm or 1/2% elongated.

That does strongly suggest the TTA torque is also TTY.

I'm getting excited to get some measurements made