[MooMooM2]

Been tracking down a noise and thought was one of the pulleys, replaced one and noise was still there, should have just have replaced all pulleys and belt while I was there. Now pretty sure its not a pulley but the belt since spraying a bit of water quites the noise)

So started doing it today, almost all done (not bad job, no space in there but very DIY). When I ordered the parts I did not even think about bolts and the whole single use BMW bolt thing. I have installed with the old bolts (they have 32k) and torqued to spec, seems fine. Have to finish the job because I do have somewhere to go next weekend and don't want to be finishing this job too close to it.

Bolts are steel, am I overthinking this? Should I just finish up the job and that be it or should I replace the bolts in a few weeks when I can?

[F87source]

Originally Posted by MooMooM2

Been tracking down a noise and thought was one of the pulleys, replaced one and noise was still there, should have just have replaced all pulleys and belt while I was there. Now pretty sure its not a pulley but the belt since spraying a bit of water quites the noise)

So started doing it today, almost all done (not bad job, no space in there but very DIY). When I ordered the parts I did not even think about bolts and the whole single use BMW bolt thing. I have installed with the old bolts (they have 32k) and torqued to spec, seems fine. Have to finish the job because I do have somewhere to go next weekend and don't want to be finishing this job too close to it.

Bolts are steel, am I overthinking this? Should I just finish up the job and that be it or should I replace the bolts in a few weeks when I can?

If the bolts were torqued and yielded (torqued to a spec like 80 ft-lbs for example, then add an extra angle twist to it 90 degrees to stretch the bolt), then you need to replace them. This is because once a bolt is stretched, it is permanently deformed as it has gone past its elastic deformation stage and into plastic deformation making the deformation irreversible. This means the bolt is now stretched and it can no longer provide the correct clamping force that bmw expects when they calculated the torque + stretch angle, also the bolt once it has gone plastic is now weakened and if you try to stretch it again you risk snapping or shearing the bolt. This is a huge PITA because now you have to remove a broken bolt that could be stuck really deep inside of a hole which is never fun. So imo always replace single use bolts.


If you must reuse a bolt, just apply the torque and don't yield it. So maybe do half or 1/4 of the stretch angle and leave it at that until you're able to replace the bolt.

[MooMooM2]

Originally Posted by F87source

If the bolts were torqued and yielded (torqued to a spec like 80 ft-lbs for example, then add an extra angle twist to it 90 degrees to stretch the bolt), then you need to replace them. This is because once a bolt is stretched, it is permanently deformed as it has gone past its elastic deformation stage and into plastic deformation making the deformation irreversible. This means the bolt is now stretched and it can no longer provide the correct clamping force that bmw expects when they calculated the torque + stretch angle, also the bolt once it has gone plastic is now weakened and if you try to stretch it again you risk snapping or shearing the bolt. This is a huge PITA because now you have to remove a broken bolt that could be stuck really deep inside of a hole which is never fun. So imo always replace single use bolts.


If you must reuse a bolt, just apply the torque and don't yield it. So maybe do half or 1/4 of the stretch angle and leave it at that until you're able to replace the bolt.

These are not TTY bolts, they were just torqued to a value and that is it. TIS just specifies a specific torque value on them. I think TIS also wants people to change bolts on the carbon brace everytime its removed.
I am tempted to just leave em be

[F87source]

Originally Posted by MooMooM2

These are not TTY bolts, they were just torqued to a value and that is it. TIS just specifies a specific torque value on them. I think TIS also wants people to change bolts on the carbon brace everytime its removed.
I am tempted to just leave em be

Some bolts are recommended to be changed even though there is not angle to the torque spec, but that's because they're still torqued to plastic deformation range. A good example is the brake caliper bolts, the front and rear caliper carrier bolts are the exact same. However only the rear caliper bolts require a torque angle, yet you have to replace them with each use. This is because the front bolts are torqued high enough to become plastically deformed, thus they're single use. Iirc the front bolts are 80 ftlbs, and the rears were like 30 ftlbs + 90 degrees.

Sometimes bmw specs to replace bolts because of corrosion issues and the risk of stripping, for instance the rotor retention bolts. These aren't torqued high enough to plastically deform yet they're replaced each time because they're so proned to coroding and stripping out.


The brace bolts are likely torqued to plastic deformation, hence why they're single use. So imo if bmw says to replace it, chances are it needs to be replaced or else you risk not getting accurate clamling loads or a broken bolt.

[MooMooM2]

Originally Posted by F87source

Some bolts are recommended to be changed even though there is not angle to the torque spec, but that's because they're still torqued to plastic deformation range. A good example is the brake caliper bolts, the front and rear caliper carrier bolts are the exact same. However only the rear caliper bolts require a torque angle, yet you have to replace them with each use. This is because the front bolts are torqued high enough to become plastically deformed, thus they're single use. Iirc the front bolts are 80 ftlbs, and the rears were like 30 ftlbs + 90 degrees.

Sometimes bmw specs to replace bolts because of corrosion issues and the risk of stripping, for instance the rotor retention bolts. These aren't torqued high enough to plastically deform yet they're replaced each time because they're so proned to coroding and stripping out.


The brace bolts are likely torqued to plastic deformation, hence why they're single use. So imo if bmw says to replace it, chances are it needs to be replaced or else you risk not getting accurate clamling loads or a broken bolt.

I will probably replace them next time I am there, I will buy the bolts and next time I have to get in the engine bay for something I will put them back on. I just don't want to disconnect the oil thermostat lines again lol, can make such a mess. Def learned from the first time I did it, this time got no oil anywhere which is great. I am replacing the rubber seals this time cuz last time I forgot to order some, no leaks but not going to do it again.

I really need to slow down when I order stuff, always forget stuff lol, cheap stuff too which I then end up having to pay big shipping for like a bolt or a washer