As per my troubleshooting to find a bike creak (Ultegra FC-R8000 Right Crank Arm Creak) - I have installed and removed the same chainring bolts ~8 times. In the process I snapped one of them. Each of my installs have used a torque wrench at 14Nm with a Torx T30 bit.

I have noticed that when installed on a crank it seems more difficult to push the T30 into the bolt, but when they are removed it is easy to slide the bit into the bolts.

Has anyone else experienced this behaviour from these (or other Shimano) chainring bolts? Am I doing something wrong if this is happening?

  • Did you buy the crankset from the LBS you mentioned in the other question? Was the one that snapped from the old crankset or the new crankset? – Superman.Lopez Jun 17 '19 at 4:42
  • I did buy the cranks from my LBS. The one I snapped was from the old crankset. The new set came with a new set of bolts so I used one from there. I'll update the other question with this - but I did try all 4 new bolts in my troubleshooting as well. – Vitamin-T Jun 17 '19 at 13:45
  • Good work - I'd replace all the bolts if one has snapped. – Criggie Feb 25 '20 at 7:23

For what it's worth - the best answer I've been able to come up with/figure out is that when I was torquing the bolts down I might have been putting force on both the crank arm and the torque wrench and maybe doubling up on the force...

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    'Every force has a equal and opposite reaction.' To tighten a chainring bolt you have to put an equal torque on the crank to keep it from rotating, that does not mean the torque is doubled. – Argenti Apparatus Jan 26 '20 at 12:47
  • I agree with Argenti, it does not seem likely. Shimano’s specs for the R8K cranks do say 12-16 Nm of torque. Ultegra should have steel bolts as well, which I’d expect to be more resistant to fatigue. Best guess is just a faulty bolt, unless your torque wrench is terribly miscalibrated. – Weiwen Ng Feb 25 '20 at 14:31
  • Hmm. I found a site that said that the 6800 version of Ultegra uses alloy chainring bolts, so I'd assume the current generation also does. Again, if the OP used the correct torque, these should not have cracked, but I do wonder if failures may be more common with alloy bolts. Most users don't need to repeatedly install chainrings. handsonbike.blogspot.com/2016/10/… – Weiwen Ng Feb 26 '20 at 19:30

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