The key is the torque process when it includes the statement to no reuse the bolts. But let's assume it is a standard bolt. Why does (not why do you think, not an opinion or guess) BMW state not to reuse the bolts?

It's not about what is the right decision. I certainly acknowledge I don't know the answer. This certainly is not standing on ceremony. It is about what information one uses to make the correct decision. I am challenging responses that are based on false premises and input that cannot be extrapolated to a conclusive decision. There has never been a trained bolt expert that is behind the decision to reuse the bolts. It always boils down to---most people do, BWW and Indie techs reuse them so it's OK. I think the decision to reuse the bolts would be the same without any input one way or the other---it is entirely cost driven.

I agree with what was said earlier---until we have an explanation directly from BMW the debate will continue--we still don't know why the statement or what happens if we ignore the instruction. IMO that information is the only information that is or can get to a conclusive answer. Please hurry, I have my X5 up on stands to change diff ratios so plate will be coming off.

It was fun for awhile. I enjoyed some of the comments. Ya'll be happy to hear I now think this is frustrating, irritating, meaningless, a waste of time, beating a dead horse and a bunch of other stuff like that. I'm glad to have provided at least some of you some laughs.

Here are a couple of links to the actual BMW bolt:
https://parts.bmwofsouthatlanta.com/...lt-31101096987
https://www.ecstuning.com/b-genuine-...r/31101096987/
If you google on the part number, you'll find the exact same bolt used in many applications other than for the reinforcement plate on the X5. That, along with everything else about it, suggests that it is a regular bolt. (well, a regular Class 10.9 ...)

The spec is TTA. Whether it actually yields or not is not certain, as far as I know. I've seen signs of deformation on some of my own bolts, but maybe that was from someone overtorquing at some point. I expect that the TTA takes it close to yield, if not into yield. So to be conservative, BMW specifies replacement, and I act as if yield occurs, whether or not it does. Yes, the fact that BMW specifies replacement, I take to mean that they think it might be yielding.

And no, yield (plastic deformation) of a bolt, in general, does not definitively mean it is not reusable. Not at all. Plastic deformation in a steel bolt will cause work hardening that strengthens it, so it should be able to return to the same amount of stretch with no further plastic deformation (all elastic now).

It's not a TTY bolt, as I tried to say. It's a regular bolt, used in an application with a TTA tightening spec, that may or may not result in yield (if yes, then TTA becomes TTY), probably causing BMW to conservatively suggest replacement, which almost everyone ignores with no ill effects.

BTW, TTA is a very accurate way to torque fasteners, regardless of yield or not. So if yield is known not to occur, a TTA spec will result in more predictable clamping force than just a torque spec.

As I mentioned in probably another thread on this general topic (search on this site, there are probably only a hundred or so to look through), the important thing to avoid is doing the TTA repeatedly. If yield is occuring, you can't keep doing the same angle, since each time, you will pushing further into the yield region, eventually causing fracture.

You asked a question, in a specific manner, knowing nobody could answer it.

I'll put it to you an equally impossible task. The E53 X5 has been on the road now for 18+ years. Each and every single one of them has this reinforcement plate on it, with these bolts. Then, cross-reference that part number with RealOEM. It is used on the reinforcement plates of every E46, E53, E65, E66, and E67 equipped with an aggregate protection plate. I don't know what the total numbers of bolts in use on all of those vehicles comes to, but it has to be a huge number. I was unable to find one documented case of failure for the bolts. We are actually the only forum that even discusses the bolts from what I can tell.

BTW: For anyone looking. Here is where you can get them for $12/each. https://www.ebay.com/p/2-X-BMW-Genui...E46/1322230484

Edit: ^ NM on the $12/ea price. It appears the "2X" for $24 is no longer available.

This was my first post when this thread was revived:

"This has been debated sooooo many times. The vast majority agree with you and reuse the bolts based on lots of members that have done so and had no problems, dealer input or what their dealer(s) has done.

If you are comfortable reusing the bolts without the knowledge as to why BMW says not to then it certainly is a cost savings. Consider the bolts are stretch to torque bolts which you can only do done once and bear in mind a single experience or the entire tally here may be accurate but the sampling is far too small to accept the results as statistically accurate. And it won't ever be. It is still an assumption either way.
I couldn't care less what anybody does and I get lots of flack when I post this input. If I didn't think it was important to throw in each time this comes up I certainly wouldn't keep doing it.

Again, the vast majority reuse the bolts."



I felt it gave credence to those that reuse the bolts and did not take a position one way or the other. Since then I have only responded to posts claiming it is fine to use the bolts that I think are based on assumptions and I don't view responses as eliminating those assumptions. I see that I made an assumption the bolts are TTY bolts. I am not convinced they aren't but I now question if they are. This has never been about which decision is right or wrong. It has been about what information has been used to make a decision.

The new information regarding the broad use of the bolts is great. If the torque specs for other uses is exactly the same and there is no statement to not reuse the bolts that is very significant.

I see this as a debate rather than a discussion Generalizing, the purpose of a debate is to present facts to eliminate flawed interpretations of information. It requires two points of view. No individual should be chastised because of their view or input. Even vailed insults are uncalled for. There should be no conclusion drawn as to whether you like a participant or not based on their input. A debate doesn't have anything to do with the kind of person one is. Nothing should be interpreted as a personal attack. It is purely an expression of a point of view. If a true debate one should be able to defend the opposite position with equal conviction. The nice thing about a forum debate is if it generates negative emotions you can opt out of the thread.

In my 1998 528i, FRONT wheel bearings bolts...BMW manual says replace them.

All BMW mechanics I know re-use them. I re-use them, they are as big as the wheel lugs.
That was 10 years ago, the bolts still hold the bearings just fine.

So what does everyone think about using duct tape? [emoji38]

Sent from my SM-A730F using Tapatalk

Duct tape will seal it, but you really need zip ties for the holding power.

I prefer JB Weld Kwik. Best thing out there. Built entire cars out of the stuff.

I don't see any doubt about them being special TTY bolts. But I think there may be some doubt about whether they yield when the TTA spec is applied properly. While responding to another thread right now on oldmactech's head bolts, I was reminded of this thing I noticed when examining my old vs. new head bolts last summer.

https://xoutpost.com/bmw-sav-forums/...formation.html

Should be an easy test for someone who actually buys new ones to compare vs. the removed ones. And if you line up old vs. new and the threads match all the way, you can pretty safely conclude that they did not yield, and reuse them with even more confidence.

Also, regarding applying the TTA, that's only part of it, since the factory, the owner, the PO, the dealer, etc. might not do it accurately. And then once applied, stresses from driving could cause some yield. So different people might find different results, even among their 6 bolts.

I've had my plate off a few times; first was for front differential oil change, last was for top-end engine rebuild. I paid attention the first or second time, noticing some deformation based on the fact that the nuts would not all spin on easily with nut and bolt in hand. So as I've said, I re-use with the conservative assumption that yield has occurred, and not wanting to yield it more, I torque accordingly to a higher but conservative value, without doing the final angle.

from BMW:

(they didn't include the protection from the garage floor, but maybe that is attributed to the foam padding above the panel).

I put my 'restriction plate' (restricts you from getting to anything) back on with some SAE bolts i had handy and am soon going to be removing the plate and putting it back on.

Since it's the way i'm built, i plan to do a ditch-witch maneuver with the plate off with some steel strap snug by not overly tight to measure how much the subframe will twist when i lift one wheel up in the air, probably drive onto a stack of cement blocks to lift it 8".

It's pretty clear that the primary job of the plate is in-fact to keep the front suspension true and not twist; 4 or 5 mm thickness of aluminum times 200mm width (my estimate) means 800-1000mm cross section that's the equivalent of a solid rod of 16-18mm diameter and would substantially hold quite a bit of force. (40-50,000# before yield with mid-grade aluminum alloy; could be double with high strength aluminum)

Since i used under performing bolts and they've been on there a while, if they didn't do their job and allowed motion, it will be very obvious. If they on the other hand, held the plate from moving in spite of being much lower clamping force than the design, it will be solid proof that bmw over-engineered the part and give people piece of mind that they can definitely use normal bolts.

The bolt i found online just now clearly is stamped 10.9. There is no reason you couldn't use a similar bolt from a hardware store except it won't be galvanized. Steel-to-aluminum will set up an ugly galvanic reaction when it gets a little salt spray on it.

The TIS for replacing the plate is here

The torque spec is here

My reference for bolt torque shows 67 N·m and the tech spec above shows to use 56 N·m + 90°. I will also see how a re-used bolt vs a new 10.9 bolt behaves when it's torqued. I have a strong suspicion that the extra 90° will go past the 67 N·m advised torque and puts you from TTA into TTY.

0.0888 in² cross section and yield of 136k psi, means yield force of 12,100# roughly and torqued normally (67 N·m / 49 ft·lb), is 'only' 7531 # of force. Another measurement I will take is what is the actual torque applied to achieve the 90° TTA.

The whole point of this endeavor is to determine if the bolts are even close to their yield strength and there is any need for this debate to continue. If the bolts aren't close to even the proof load of 113kpsi, the debate can be concluded. No damage to the bolt and no reason to not reuse them.

If, on the other hand the bolts are being stretched to yield, then my recommendation would be to slightly under-torque to keep them from stretching or oversize the bolts one size bigger so you can get the same clamp force without damaging the bolt.

A little quick math achieves this factoid: it takes about 89 N·m to get a 10mm 10.9 bolt to proof load, which won't hurt the bolt at all, and about 107 N·m to get that bolt to deform. So, if the 90° after 56 N·m is in the range of about 100 N·m the bolt won't deform and you can reuse it as many times as you'd like; until you hit the limit of elasticity steel acts like a spring and you can basically use it countless times (think of coil spring on a car how many millions of compressions; yes they can fail, but wow it's not likely).

So here is another interesting factoid: switch to fine pitch thread and you can bump the clamping force from 7500 to 8400# per bolt. That would likely be easier than drilling out a hole to 11mm (and finding 10.9 M11 bolts!).

So my summary is that if it can be determined that 56 N·m + 90° ends up at less than 100 N·m of force you did not deform the bolt and it can be reused without any concern.

I am almost certain that the design of the system is that it uses the bolts beyond the advised torque and clamp force on purpose to achieve two significant results: 1; that it will keep the plate from slipping sideways so it can do its job and 2; that it won't wiggle loose; the added forces are simply acting like a lock washer. Similar to the concept of head bolts; using a pre-tension and angle gives you a very precise force based on the elasticity of the steel and simple math (how much longer did you stretch the bolt).

I scoured the 'net to see if anybody ever did any actual tests or experiments on this stiffening / reinforcement plate and found hundreds of posts posing the question and not a single example of finding an answer. It won't be that difficult to figure out a definitive answer, which will certainly give 'seat of pants' guessers some satisfaction that they guessed correctly.

I'm planning to remove my underbelly plate and wife's as well in the next couple weeks to do some hard-core engine cleaning and finding some wayward leaks, so i will do a couple tests when i do so to determine the answer people have been pondering for years yet nobody took the HOUR it will take to answer them.