Stiffening plate bolts

[bcredliner]

Originally Posted by crystalworks

Replying here as it makes more sense here.



By this reasoning none of us should be turning wrenches on a BMW, or any other car for that matter, as we are not trained auto technicians. Or working on our houses because we aren't contractors, or any other number of examples. A bit reductio-ad-absurdum admittedly. But to say that anecdotal evidence and personal experience of members should be disregarded (especially one as mechanically inclined as Andrew) is like saying we should all ignore our father's when he is trying to teach us something. Doesn't make sense.

As I said, BMW recommends replacement of suspension fasteners as well. But they routinely go unchanged during maintenance. If the stiffening/reinforcement/skid plate bolts/nuts were $1/ea I still doubt many would replace them due to inconvenience, just like the suspension fasteners. I'm sure the dealerships would stock and replace them if they were so cheap. Many more DIYers than do now (which is in low single digit % I'm sure) would replace, but most would just zip them back on and not think twice.

We all understand your position. BMW recommends replacing the bolts every time they are loosened. You've stated it, we accept that, or at least I do. You do as you see fit obviously. We disagree that they need to be replaced. We've stated it, along with our experiences.

If someone comes here asking about whether they need to be replaced or not, our responses would be wildly different. Yours would be: "BMW recommends replacing them." That should be the end of that as no one knows why BMW recommends that. Our responses would be, "BMW does recommend replacement, but not many here do, we don't see a reason to, and my/our experiences are..." There is no debate that needs to happen... and yet it does.

I will assume I didn't make myself clear so I'll try again--Neither of us was part of the BMW design team. Whether we defend new or reusing bolts we can offer nothing more than an opinion based on our experience. We don't know what we don't know. My post had nothing to do with DIYing which is always a good thing if for nothing more than a contribution to self esteem.

I am not questioning anyone's personal experience. I am clearly stating it should not be used as a definitive answer.

I don't see my responses as debating. I don't know what the right answer is. I respond to posts that defend not using the bolts using an invalid premise. That is completely different. I am not debating a point of view. I am challenging the basis for drawing the conclusion to reuse the bolts and telling someone, who is asking what to do, to reuse the bolts. IMO that is a disservice to that member.

When you post something that is a valid and a definitive basis for reusing the bolts I will thank thank thank you. I don't like paying the price for new bolts.

[tartilla]

Long post about fasteners.

The plate is being pressed to the mounting frame in 6 locations. The pinch force needs to exceed the lateral force potentially generated, or it would 'work' the fasteners, putting them into a shear loading.

All fasteners act on an elastic concept. I cannot say why the BMW engineers spec'd TTY hardware. But really, all they arw doing is giving a clamping load for pinching the metal parts together.

Any fastener that has sufficient tensile and shear strength, that meets or exceeds the originals, should be ok.

My old Mack dump truck, occasionally breaks wheel studs on the front. They're about 1.5" diameter. 550ft lbs. Tq spec. They must be getting fatigued from a shearing force, that crystallizes the shank, and eventually a fault line is created...then you have a nut and 1/2 stud cruising down the road, sans vehicle...and me changing out 3 new hard to source studs.

I don't doubt that the sheer panel ads rigidity. If not tightened enough, there may be movement at the contact points, and noise may be a symptom. Doesn't seem to be too common, only 1 complaint in the whole thread.

I suspect, I'll source some good 12.9 bolts after I have a look at the panel, and how it affixes to the 4.6. I'm not keen on an open nut system, but it's the easiest and most reliable...and works in a pinch.

Carroll Smith's book... Nuts Bolts Fasteners and Plumbing is a great resource.

https://www.goodreads.com/book/show/...mbing_Handbook


BMW engineers, are still beholden to the laws of physics. They have not always made the best calls. But they've had some great wins as well.

I only wish I could have a GM LS engine, 302ci, with a 3" stroke singing at 8000, in a BMW fit and finish vehicle...Best of both worlds.

[bcredliner]

"Any fastener that has sufficient tensile and shear strength, that meets or exceeds the originals, should be ok."

Should be OK, or is definitely OK?

[crystalworks]

Uh oh.

Edit: tartilla, here is a link to the thread where this has been discussed ad nauseum. Andrew did some great testing in there and came to a determination about reusing the OE bolts, replacing them with cheaper alternatives, and torquing techniques. https://xoutpost.com/bmw-sav-forums/...llation-7.html

[tartilla]

Originally Posted by bcredliner

"Any fastener that has sufficient tensile and shear strength, that meets or exceeds the originals, should be ok."

Should be OK, or is definitely OK?

Well, as any informed person using the internet, it's always best to never use absolutes.

The truth is...even the BMW engineers, with their TTY spec, cannot guarantee 100%. The science just says that it's the most likely outcome.

None of us can hide from physics, but even our understanding of it, is really only in it's infancy.

But we've become pretty good predictors.

[tartilla]

Originally Posted by crystalworks

Uh oh.

Edit: tartilla, here is a link to the thread where this has been discussed ad nauseum. Andrew did some great testing in there and came to a determination about reusing the OE bolts, replacing them with cheaper alternatives, and torquing techniques. https://xoutpost.com/bmw-sav-forums/...llation-7.html

Thank you for the link. Seems I missed that post.

I'm not against the replacement of certain bolts like TTY per say.

My Mack U Bolts at 1-14" and the 1800ft.lb tq spec, I would never re-use them. Despite the extreme cost and poor availability. An extreme example.

Head bolts would be another area of concern.

I'll be yanking my plate off soon, so I'll have more perspective. Hopefully no curses.

Great forum here, by the way. Lot's of good info, and community.

[bcredliner]

Originally Posted by tartilla

Well, as any informed person using the internet, it's always best to never use absolutes.

The truth is...even the BMW engineers, with their TTY spec, cannot guarantee 100%. The science just says that it's the most likely outcome.

None of us can hide from physics, but even our understanding of it, is really only in it's infancy.

But we've become pretty good predictors.

I don't care whether folks replace the bolts or not or if they decide to use a different fastener.

My input is not what is the right course of action. It has always been about what is known and/or considered when making the decision. What is not known is the reason BMW chose to use a particular bolt in that application. IMO without the basis for the BMW decision any other conclusion is flawed. That doesn't mean a decision to go another route is a bad one but it does mean it is a conclusion without the knowledge of a critical piece of information from BMW.

[Fifty150hs]

One can have their cake and eat it too. You can order the same grade, size and type of bolts from Belmetric.com for about $20 total. So, by the less expensive bolts every time and torque them to spec and you will always be doing what BMW says, but at significantly lower cost.

[Purplefade]

You can also buy them from FCP Euro, yes, they are more than $20, but because the are TTY bolts and considered single use by BMW, FCP Euro will replace them for you for life under their lifetime warranty program . Buy them once and replace them free for life.


Sent from my iPhone using Xoutpost.com

[Fifty150hs]

Originally Posted by Purplefade

You can also buy them from FCP Euro, yes, they are more than $20, but because the are TTY bolts and considered single use by BMW, FCP Euro will replace them for you for life under their lifetime warranty program . Buy them once and replace them free for life.


Sent from my iPhone using Xoutpost.com

True, but you will have to pay to ship them both ways. The only thing they refund is the value of the bolts.