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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Suspension | Brakes | Chassis > Torque + 90 degrees - why??



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      08-16-2017, 12:39 AM   #1
dleccord
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Torque + 90 degrees - why??

why do you have to apply a certain amount of torque to a bolt/nut and then turn it 90 degrees? why not just give the final torque reading that includes the 90 degrees?
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      08-16-2017, 10:25 AM   #2
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Stretch Bolts - these fasteners are designed to stretch some at their final torque setting. The initial torque value gets you to the torque value that is the starting point for the part of the tightening process where you actually stretch the bolt by turning it an additional 90 degrees (typically 90 or whatever is specified). This is a one time process and thus the need to replace thees types of bolts in most use case situations - they are generally one time use, otherwise you stretch them again and they are beyond design spec and could shear / break.
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      08-16-2017, 10:39 AM   #3
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^^
Great answer.
/thread
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      08-16-2017, 10:52 AM   #4
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AvE explains it here too, embed seems to pick a random time but around 9:30 onwards he explains it -


Basically because they know how far the nut moves in that space it's actually far more accurate than torque rating, which can vary depending on friction etc.
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      08-16-2017, 11:19 AM   #5
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Quote:
Originally Posted by Digitalize View Post
Basically because they know how far the nut moves in that space it's actually far more accurate than torque rating, which can vary depending on friction etc.
This right here ^^^

Quote:
Originally Posted by Speed_Addict View Post
Stretch Bolts - these fasteners are designed to stretch some at their final torque setting. The initial torque value gets you to the torque value that is the starting point for the part of the tightening process where you actually stretch the bolt by turning it an additional 90 degrees (typically 90 or whatever is specified). This is a one time process and thus the need to replace thees types of bolts in most use case situations - they are generally one time use, otherwise you stretch them again and they are beyond design spec and could shear / break.
Your first reference is to torque-to-yield (TTY) bolts. Your second reference is to torque-to-tighten (TTT); which is not a bolt but a procedure used for tightening fasteners. TTY fasteners are often tightened using the TTT method, but both are obviously two completely different things.

Pretty neat article on that here if anyone's interested:
http://www.boltscience.com/pages/a-c...tightening.pdf
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      08-16-2017, 04:42 PM   #6
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Are there incidents where BMW snapped their suspension bits due to not replacing nuts and bolts?
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      08-17-2017, 11:42 AM   #7
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Quote:
Originally Posted by dleccord View Post
Are there incidents where BMW snapped their suspension bits due to not replacing nuts and bolts?
You won't find a lot of aluminum fasteners holding the suspension pieces together. That's where I'd be most worried of breaking bolts while trying to recycle them.

Any of the other TTT bolts I'd be weary of using factory recommended tightening procedures on more than a few times, for sure.
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      08-17-2017, 12:20 PM   #8
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A lot of bolts are CAD plated that resemble aluminum and often people mistake them for aluminum bolts.
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