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#141
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AM.
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E70 2010 3.0 M57 AT Titanium Silver with Black Leather E53 2004 3.0 M54 AT Toledo Blue with Gray Leather E83 2008 3.0 N52 AT Silver Gray Metallic with Black Vinyl E46 1999 2.8 M52TU 5MT Black with Tan Leather 250K+ miles (Sold, but not forgotten) |
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#142
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Why does BMW state not to reuse the bolts and what can happen if they are reused?
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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior Dallas |
#143
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85 or so percent of torque is friction. The other 15 percent is clamping power. If there is deformation there is no torquing procedure that will get to the original clamping power. Why does BMW state not to reuse the bolts and what can happen if you do?
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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior Dallas |
#144
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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior Dallas Last edited by bcredliner; 04-03-2019 at 08:10 PM. |
#145
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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.
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1998 E39 528i 5sp MT 2006 E53 X5 3.0 6sp MT |
#146
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Stiffening plate removal / reinstallation
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.
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2011 E70 • N55 (me) 2012 E70 • N63 (wife) Last edited by andrewwynn; 04-03-2019 at 09:06 PM. |
#147
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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.
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2011 E70 • N55 (me) 2012 E70 • N63 (wife) |
#148
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Using basic tools (peak reading torque adapter) and micrometer it will not be difficult at all to determine several things: Are the bolts stressed to plastic deformation mostly is the key. If they are not simple formulae exisit to determine the clamping force. Taking a new bolt and tighten TTA per spec and measure the torque to get there. Remove the bolt and meausue it's length before and after to determine if it's been stretched. If not plug the torque value into the torque to force calculation and you'll get the clamping force within 10-20%. You don't need anything particularly NASA grade to figure this one out it's not mission critical like a head bolt. It's my contention that it's an over enginereed part and I plan to test that in a real world way and report the findings. If I'm wrong I'm completely fine with that I'll just use a bigger bolt to achieve the factory design without self-destructive bolts. It's the blind faith following with no explanation that bothers me and surely tons and tons of others (based on the thousands of posts easily found on the internet on the topic). If we knew for example that the plate moved a mm every pothole if you attempted to reuse the bolts that's information we can use to side with BMW. If we knew that you could use a 3/8" unhardened bolt for a year and have no sign of sideways slip, that's hard evidence to support single use on the bolts is a crock of crap. The reality is somewhere in the middle I'm betting.
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2011 E70 • N55 (me) 2012 E70 • N63 (wife) |
#149
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You can loosen the bolt and then tighten it to the exact same strain (torque angle, bolt stretch, however you want to measure it) and it will have the exact same clamping force. Theoretically of course. Nothing is really exact. But practically true as well.
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2001 X5 3.0i, 203k miles, AT, owned since 2014 |
#150
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2006 Infiniti G35 2001 BMW 3.0I E53 X5 Build date 08/2000 SOLD Lotus Europa 1970 Destroyed by fire Lotus Europa 1970 S2 Renault Powered Lotus Type 52 1970 Twincam Webers Powered PORSCHE 911 Targa 1982 The Garage Queen Audi Avant donated to Kars for Kids BMW 525IT Sold Audi 4000CS Quattro Sold Jensen Healey Lotus Powered Sold Opel 1900 Sold Triumph Spitfire 1971 Sold Triumph Spitfire 1968 Sold Plymouth "Cuda" 340 Six pack SOLD |
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