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I was given a brand new carbon mountain bike by my uncle, he assembled it himself about 18 days ago. My problem is that I am not sure if he used a torque wrench when he assembled the bike.

I would like to check if the bolts have the correct torque so that they won't or aren't damaged yet. Is it possible to check the torque of already tightened bolts? If not then how should I check for possible damages that my bike could have gotten?

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  • 2
    Generally, the rule is that if it didn’t break during tightening, it’s not going to break in service.
    – MaplePanda
    Oct 10 at 17:00
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    I guess the obvious solution - ask your uncle if he used a torque wrench when he assembled the bike - is not possible for some unknown reason.
    – emory
    Oct 11 at 2:10
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He is unlikely to have damaged anything unless he's a complete gorilla.

Loosen off any bolts or bolt pairs that you are concerned about, then do them back up to torque.

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    Components like built-in carbon seatpost clamps and carbon handlebars (or steerer tubes) can be quite sensitive. It’s easy to accidentally reach 6Nm or more with your hands.
    – Michael
    Oct 10 at 17:53
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I guess you could set your torque wrench to a slightly higher value (e.g. 4.5Nm instead of 4Nm) and see if the bolt moves when you try to turn it. If the bolt moves you know that it hasn’t been tightened to more than the specified value (at least when it was tightened the last time).

Afterwards it’s probably a good idea to revert back to the specified value. The temporary, small increase beyond the specification should be well within the component’s tolerance (assuming your torque wrench is accurate).

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    Clarify please - are you suggesting OP overtightens the bolt? Or undoes the bolt using the slightly-higher torque setting. It is not clear which way you're suggesting they turn the fastener.
    – Criggie
    Oct 10 at 18:25
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    Unless the fasters are prepped correctly, the clamping force for the a specific torque can vary by 50%. Over torqueing by 10% ain't going to break anything. Reason for the obsession with torque wrenches on bicycles is to prevent gorillas with spanners over torqueing by factors of ten, not two. Not many bicycle torque wrenches are regularly calibrated, most the value is 'taken as read' and presumed to be correct out the shop. (c.f. Aviaiton where critical fasteners are always brand new, prepped according to manufacturer spec and wrenches have calibration certificates.)
    – mattnz
    Oct 10 at 21:03
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    Note that movement may not occur unless the wrench is set significantly higher than the tightening value because the coefficient of static friction is usually higher than that of dynamic friction.
    – MaplePanda
    Oct 10 at 22:36
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    A bolt that has been tightened a while ago usually takes significantly more torque to start moving again - more than just the static vs. dynamic friction difference. I'm not sure about exactly what causes this, but the behavior is probably familiar to many.
    – jpa
    Oct 11 at 6:42
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    @jpa metals do form bonds over time, especially if one is aluminium
    – Chris H
    Oct 11 at 10:17
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When in doubt, do them yourself. Use reasonable force to loosen them, and tighten them back in to spec. If a bolt doesn't come out, try using PB Blaster or WD-40, or similar. If that doesn't help, you can either try a powered torque driver (carefully, to not crack the frame or strip the threading), or just accept that they are bonded. This is good practice whenever you are depending on a bolt that isn't coming from a quality-checked factory. (ex: getting tires changed at walmart - Its a lot better to spec them in your driveway than try to wrench > 200 ft-lbs on the side of the road in the rain)

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  • Not sure if PB Blaster or even WD-40 will harm carbon composite.
    – Armand
    Oct 11 at 17:51
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    Be VERY aware that if any of the lubricant (WD-40/PB Blaster) is left on the threads, you will tighten the bolt significantly above the torque wrench setting because the threads are lubricated. The lubricant will reduce the friction that the wrench relies upon. Once threads are lubricated like this, they will require significant mechanical drying (wipe it down multiple times), then let it air dry for a while (several days, maybe?) to allow any remaining lubricant to evaporate. If there is a factory spec for a lubricant, apply it after this cleaning/drying process.
    – FreeMan
    Oct 12 at 14:20
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I’d look and see if you still have the assembly instructions and if not search them on the web. Once you’ve acquired the specific torque specifications for your said model. Then acquire a torque wrench tool and then you can follow the instructions and proceed to check the bolts of concern.

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