Stiffening plate removal / reinstallation

[cn90]

Could you do the same measurement for a wheel bolt?
We re-use wheel bolts all the time and wonder what the wheel bolts look like after 15 years of service...

[Crowz]

Originally Posted by cn90

Could you do the same measurement for a wheel bolt?
We re-use wheel bolts all the time and wonder what the wheel bolts look like after 15 years of service...

Or even shorter time periods after tire shops nail them with air tools....

[andrewwynn]

Originally Posted by cn90

Could you do the same measurement for a wheel bolt?

We re-use wheel bolts all the time and wonder what the wheel bolts look like after 15 years of service...

Unless they are over torqued they will last forever. It isn't that hard to over torque though.

Case in point:



I goofed above when I said the lug bolts were M12 they are M14.

M14 spec is 187 N·m and BMW calls for 130 so 40% safety margin on not damaging the bolt.

The bolt above I believe was tightened with 350 ft·lb impact

I use torque sticks just like the shops. When I spot check with digital torque wrench they are within 6-8% I don't race I'm good with that.


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[andrewwynn]

Originally Posted by cn90

Could you do the same measurement for a wheel bolt?
We re-use wheel bolts all the time and wonder what the wheel bolts look like after 15 years of service...

did you see the picture of the lug bolt that was over-tightened? I've recently removed over-torqued lug nuts and bolts that were more than double the spec.

Fortunately there is a decent amount of overhead that a normal person using a lug wrench is not likely to over-torque them but could by stepping on it pretty easily, but with impact it's quite easy.

Advised torque for M14-1.5 10.9 bolt is 202 N·m and BMW spec's 130 on at least my x5, not sure if different on the M sport or E70s.

Each bolt can handle 16,200# force, but that's at full torque, it's 'only' 14,169# per lug bolt at 130 N·m. that is 70,845# per wheel when properly tightened.

yield is 20% over proof so you will damage a lug bolt at about 180 ft·lb, (242 N·m)

[crystalworks]

Originally Posted by andrewwynn

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

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

Interesting. Thanks for the pics. I'll have to measure mine as well next time they are off. Get a second point of reference. But to throw a wrench into measuring the old bolts... we don't know their history of torquing. Most mechanics just hit these with an impact, give it a few good uggaduggas, and call it a day.

[bcredliner]

Originally Posted by andrewwynn

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

There are multiple pages that you posted the bolts can be reused with no qualification of the number of times and prior to posting disagreed with the Fastenal information. Since the bolt is elongated that means the same amount of torque will not result in the specified clamping power. In the testing world instruments can be used to measure the angle increase necessary to reach the specified clamping power. In the real world there is no way to know what amount of elongation equates to what amount of angle increase.

[andrewwynn]

One last point: BMW is very subtle about the reuse factor it's almost just a footnote it's not like the verbiage of driving without the plate.

Paraphrasing: "under no condition drive the car without the stiffening plate*"

*And if it's not too much trouble you should really consider using new bolts.

The first time through the repair manual I actually read "replace the bolts" meaning re place the bolts you just removed back into the plate. It took a half a dozen re-reads of the TIS before I was confident they do actually recommend using new bolts.

[upallnight]

Originally Posted by andrewwynn

One last point: BMW is very subtle about the reuse factor it's almost just a footnote it's not like the verbiage of driving without the plate.

Paraphrasing: "under no condition drive the car without the stiffening plate*"

*And if it's not too much trouble you should really consider using new bolts.

The first time through the repair manual I actually read "replace the bolts" meaning re place the bolts you just removed back into the plate. It took a half a dozen re-reads of the TIS before I was confident they do actually recommend using new bolts.

This caution is more for people that remove the stiffener plate but don't reinsert the bolts to secure the sway bar bushing back onto the subframe. People are stupid and don't realize that when they remove the bolts for the stiffener plate they are also detaching the sway bar from the subframe.

It would be a lot more dangerous driving around with the sway bar detach than it is with the stiffener plate removed.

[bcredliner]

Originally Posted by upallnight

This caution is more for people that remove the stiffener plate but don't reinsert the bolts to secure the sway bar bushing back onto the subframe. People are stupid and don't realize that when they remove the bolts for the stiffener plate they are also detaching the sway bar from the subframe.

It would be a lot more dangerous driving around with the sway bar detach than it is with the stiffener plate removed.

You are correct. In my Bentley 2002 X5 service manual there is one box that reads:
"Caution
Do not drive vehicle with reinforcement plate removed. Reinforcement fasteners also serve as stabilizer bar fasteners"

As you well know the second box is what applies to the discussion.

It starts with

WARNING

Below that is the box. It reads:

WARNING---
Do not reuse self locking fasteners. They are designed to be only used once and may fail if reused. Replace with new"

[andrewwynn]

Originally Posted by bcredliner

WARNING---
Do not reuse self locking fasteners. They are designed to be only used once and may fail if reused. Replace with new"

I missed this earlier; that's the NUT they are describing here. So as I surmised, they should also be 'single use' as they are crushed locking nuts def. not meant to be re-used.