6

I have a bike that is no longer in production, but it has a standard drivetrain (FSA). I had some shifting issues the past couple days, and to my surprise when I did a clean/inspect, three of the 5 chainring bolts had dropped out and the other two were finger loose.

I salvaged some bolts from my donor bike. I needed a breaker attachment to my 5mm hex to get them off. There was no residual threadlock on the threads. Now I'm unsure how hard I should tighten them onto the first bike.

Why would they have come loose in the first place? How hard should I tighten them to prevent this from happening again? Would a dab of threadlock be good insurance?

4 Answers 4

9

A Shimano "General Operations" manual states the tightening torque for road chainwheels is 12-14 N-m. For mountain bike chainwheels it's upped to 14-16 N-m for large and middle ring and 16-17 N-m for the smallest ring of a triple. The website: http://si.shimano.com/#/ The manual number I'm referring to: DM-GN0001-20-ENG.pdf Blue loctite or equivalent threadlocker is indicated here as well. I can't accurately surmise the cause of the loose and lost bolts in this specific case. However my experience with situations of loosening bolts or part failure due to "coming apart" in various mechanical settings often comes down to incorrect or incomplete tightening of the fastener (bolt, nut, etc). Part of this process is rechecking the fastener's torque after a break-in period of normal use.

3
  • Hmm.. What does "rechecking and retorqueing" entail? If it's to retorque without first removing a bolt, that would destroy the previously applied Loctite. If it's to first undo a bolt (as is suggested by "those who know"), add Loctite and then torque, that would mean an infinite loop, since the count for torquing would be back to zero and a subsequent retorqueing would be necessary.
    – Sam7919
    Commented Oct 17, 2023 at 14:52
  • 1
    Semantics. After a ride or two, set the correct torque on the wrench and go around the chainring bolts making sure they're at least at the spec torque. Personally, I prefer thin layer of grease on the threads and where the bolt and nut interface with the chainring and spider. Seems best for preventing noise, galvanic corrosion and allows for reaching proper torque without falling of the metal. So perhaps "recheck the torque" is better wording
    – Jeff
    Commented Oct 18, 2023 at 17:04
  • 1
    A less stickling reading of the answer should result in someone who wants to follow the advice placing a torque wrench on them again and checking the work.
    – Jeff
    Commented Oct 18, 2023 at 17:14
6

Park tool has a great reference Here (all inch-pound) Chainring bolt- steel

Shimano 70-95

Campagnolo® 84-120

Race Face&erg; 100

Truvativ® 107-124

Jury is out on thread lock on chain ring bolts. A do not believe a light thread lock will hurt ( until you need to remove them), but also believe correctly tightened bolts should not need it. The problem is the little two prong thing used to hold the nut is unlikely to allow a decent torque.

Better to give the threads a good clean and lightly grease the threads.

3
  • I use low strength loctite 222 on the bolts and always carry a spare chainring bolt
    – Vorsprung
    Commented Nov 28, 2018 at 13:01
  • 2
    If tightened to the correct torque, I have never had a chainring bolt come loose with the application of light grease. I agree that thread lock could cause more problems than help.
    – Rider_X
    Commented Nov 28, 2018 at 14:27
  • @Rider_X Do you mean to grease the inner threads so as to prevent crossthreading or grease the outside of the female part so that it plays more freely in the chainring recesses? Also what grease do you use? I will cinche down to bolts to the specified torques without chain lock and look after them for a week to see how they fair.
    – AdamO
    Commented Nov 28, 2018 at 15:04
3

On my race BMX's I put cable ties through the chain ring bolts once they are correctly tightened as this prevents them falling out if they come loose. You need to still check them regularly to ensure that they have not come loose.

Cable ties are a good insurance policy to stop them dropping out.

3

I actually joined this site due to the bad advice on this post--the Shimano recommendations (~14 Nm) posted on here are about double what the torque should be for my application--ask me how I know--using such sheared the head clear off one of my bolts ; ( Very uncool...

Better advice is to consult a toolmaker's recommendations...

I recommend Park Tools listing (below)--you should consider that chain ring bolts can be made different ways and of differing materials...take multiple data points on recommendations and/or ask a LBS (local bike shop) mechanic before proceeding.

https://www.parktool.com/blog/repair-help/torque-specifications-and-concepts

3
  • 1
    Shimano’s general documents advised 12-14 Nm. Park advised 8-11 Nm for steel, less for aluminum. That’s a discrepancy, but it’s not like Park is advising half of what Shimano is.
    – Weiwen Ng
    Commented Dec 17, 2021 at 18:23
  • 1
    Per Park Tool:Chainring bolt: aluminum Shimano® 5–10 44–88.5 Which matched LBS advice of 7 Nm...which is double the posted "Shimano recommendations of 14 Nm" (Note the difference could be that my chainrings are a triple set, threaded into Aluminum crank as-is, no backing nuts) Commented Dec 17, 2021 at 18:43
  • 2
    I can't fathom taking a tool's torque recommendation over the application's manufacturer's torque recommendation. I've got an 18" breaker bar - it's probably good for 300+ ft/lbs of torque. Should I use the tool's recommended torque for a chain ring bolt? That makes no sense! You only use a generic recommendation when a more specific mfgr recommendation can't be found. I'd imagine that your issue had more to do with miscalibration of or incorrect settings on the torque wrench.
    – FreeMan
    Commented Oct 18, 2023 at 17:55

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.