You guys talk about bolts and nuts. For my 2013 X5 E70, there are no nuts per se. All the bolts go directly to the subframe steel beams. Are these still TTY bolts? Thanks.

Without "tone" it can be impossible, but in this case as mentioned I saw only objective input. At times maybe a little more tight tolerance than the scope of DIY repair. Like I mentioned I'm looking for real world answers not 1% tolerance. In this endeavor the goal is to find out with a home brew test, what is a reasonable solution and if there is one.

I'm convinced I've found enough research from other people's testing to determine that it's absolutely ok to reuse the bolts at least a couple times.

There is literally ZERO info on the web that can give us a solid answer as to why, either way. In a way, @bc making the point that nobody that "just does" (reuse the bolts) never came up with any "how" to properly do that without compromising whatever reason that surely was there. This type of pushback just is rational thinking and I'm ok with that it helps me dig deep enough to find actual facts.

I may have missed something in my search without being hard-pressed to find proof.

I believe I have. The evidence will be coming soon.

Sooner than planned as it turned out: Lumba2 developed a horrible dry ball joint sound in the front end and I can't see where so plate coming off today.

https://uploads.tapatalk-cdn.com/201...3bb9f7e286.jpg

So: results!

I took the plate off my wife's car and it was certainly removed in the past as the front bolts came off with 45 and less than 20 ft·lb of torque!

The back four bolts took between 58 and 68 ft·lb to remove and that was inline with the results when doing repetitive testing at TTA.

So this is just a quick report because it's solid info.

I have to repeat the test with some new bolts.

So what did I discover?

• when torqued to spec (56 N·m + 90°) the bolt was 0.37mm longer, almost exactly the mathematical result of 3/8.

• when the tension was removed, the bolt was 0.08mm longer, which is inline with if my earlier example was reused 3-4x in the 18 years.

• using 56 N·m preload the bolt didn't stretch even 0.001"

• the first re-tighen (of MY doing) the bolt took about 103 N·m to get to yield

• each successive re-tighen it took about 3 N·m less (103 100 97 95 92)

• I could really feel the drop off in force by the 4th attempt so on 5th time I decided to twist more than 90°

• there was virtually no increase in N·m torque to go between 90 and 120° then BANG! One bolt becomes two!

I need to test a new bolt but it looks like I was VERY CLOSE to the five use estimate.

The first three re-tighen tests I could really feel that the bolt was fighting me it took increasing solid effort the full 90° swing. The last two I could very much feel the drop off in resistance and were definitely past useful life.

I have no history on these bolts so don't know how many times they've been recycled but at least once.

At this point I would very confidently use them 3-4x without a question, they felt just the same during the torque to angle, but i have to see what the results are with new bolts.

I was thrilled when it popped. It may have gone 5 more cycles if I stuck to 90° but I'm behind schedule I have to wrap things up.

If you use a digital torque wrench like me you could also feel for the yield zone. If the bolt (dry) yields above 100 N·m it's not past it's useful life in my determination. If you can't get 95 N·m at 56 + 90° it's shot I would not use that bolt.

I will do a complete write up and also I'm planning to use 12.9 bolts for my cars and will of course include the findings there as well..

So the short summary; re-use? Yes, until dry torque at 90° is less than 95 N·m (I may be revising that # down or up after I get new bolts to repeat the experiment.

"My thoughts on the idea of "just return under warranty" for a bolt that is designed to be single use is that is a consumable item and gaming the system do to the fine print working in your favor is cheating/stealing in my opinion. How is that different from an oil filter?"

NO "gaming the system" as FCP even says you can essentially do oil changes for life for free, including oil filter. That's their deal and that's what they sell. No "gaming" just abiding by what FCP sells. That's why some have suggested buying the bolts from FCP and returning them for refund when replacing. That's what FCP sells. LIFETIME WARRANTY on everything they sell.

Stiffening plate removal / reinstallation
 

I guess like "free shipping" fcp has to decide what items they can sell without losing money like those as an example.

If FCP it ok with it that's just very unusual but if it's a loss leader to get you to keep you coming back good on them. I may have to check them out.

I just did check 'em out and I stand corrected they do literally say "even the parts that wear out".

Nice thanks for pointing out the craziness of FCP.

Bought a new turbo for my A4 from FCP, $1360. The wastegate pivot is a known weak point, they sometimes fail as soon as 40k miles. FCP assured me they would replace it no questions asked. We're eventually going to find out.

The only thing most peoples like myself do when reusing the bolts and nuts is that we just tighten them with an impact and forget about the 90 degree additional turn.

1+,

I tighten to 56 N·m + 45°.
That is good enough for me.
The 90-degree thing may be too much, actually 56 N·m + 90°) will bring the torque to the same as a typical wheel lug, which is usually M14, not M10.

Anyway, for me, it is 56 N·m + 45°...
I have done this several times, maybe 4-5 times, zero problems.

To what torque is the problem; completely randomness with 'impact'; somewhere between 20 and 100 ft·lb. My wife's six bolts ranged from about 20 to 68 ft·lb to remove (the properly torqued when tested were within about 65-70 ft·lb to remove).

The preload of 56 N·m will be plenty for the purpose of the anti-sway bar, but will not do a great job of holding the plate against shear (BMWs main purpose of the bolts/plate).

I'm going to do a test of what if any motion on the plate when the bolts are not torqued properly.

The corner mount is not just a plate of steel to aluminum; the bolt hole on the frame is a solid donut of steel about 1.5" in diameter and 1" thick welded to the corner of the subframe on steel plate about 6mm thick; it could easily handle 20,000# of diagonal force.

I will examine my wife's anti-flex plate when i get back home; one side was very loose and if there is any concern of does it move, it should show an oval wear where the aluminum slid over the steel donut. In addition My car I used 'seat of pants' or maybe i used 60-70 ft·lb straight torque to put them on (I would have looked up the standard torque of 3/8 or M10 bolt), so i will likewise examine mine for motion wear.

I also plan to tighten the bolts to maybe half normal clamping force and put the car through some stresses that should move the plate; i'll take video to see if it actually moves and determine if there is any need to even worry about it.

Also, I was thinking along the same idea above of pre-load and 45°, it may be a very good way to get a semi-consistent clamping force, but in reality, lubricated straight torque will likely be better; i will do some tests with the 45° concept shown above; i don't think that will achieve a consistent clamping force, because each bolt will have different cross section and hardness each re-use.

Case-in-point when i put wife's bolts back in on the back to hold the anti-sway bar, i used 56 N·m + 90° to tighten them, and measured the torque required to get there; the first two averaged about 105 N·m which matched pretty close to the one i tested to failure, but the 3rd took about 110 N·m and the forth I got to about 117 N·m before i even got to 90° and it was still climbing. (i'm betting that bolt actually was replaced so that was the 2nd use).

I think there are two reasonable re-use philosophy options;

1: use a lubricated straight torque to a value less than yield, that will get a reasonable percent of design clamping force, say 80% and that will not require replacing the bolts really ever.

2: keep track of how many times re-used and use them 4 or 5 times before repacking; if you have a peak-reading torque adapter, replace any bolts that get below 97 N·m during the 90° tightening phase.

(those values are preliminary).

I don't know what bolts are used on 2013 X5s. Sorry.