One chainring bolt on my super record has fallen out 4 times. I have 2 more left ( it's like Flight of the Phoenix!). I obviously need to glue this one in but does anyone have any suggestions as to what glue to use. The LBS put lots of (blue Loktite?) but it clearly needs stronger stuff. What could I use and what may the consequences be? ie might it be stuck for ever? Both chain rings are relatively new and I would hope for at least 2/3 years out of them.
Thanks
Chesters
Chainring bolts falling out
Re: Chainring bolts falling out
you are talking about a four-bolt version I guess?
IIRC these bolts are of conventional type but made in aluminium and use a torx fitting.
Blue thread lock works as a lubricant as the bolt is tightened but then acts to prevent the male part and the female part from unscrewing from one another. The stuff can be pre-applied as a paste which contains micro-capsules; the micro-capsules burst under pressure and release the locking agent. IMHO it is extremely unlikely that the male part of the bolt would be able to back itself out five turns or so without you noticing that something is wrong, if the threadlock is properly applied.
You say that the bolts come undone; if you find one half of the bolt remaining in the crankset this seems likely. However if you don't find either half of the missing bolt, I'd suggest that it is also possible (likely in fact) that the bolt has simply broken and both halves have dropped out.
As a general rule I don't like aluminium chainring bolts; they gall as they are tightened (unless copiously lubricated), they suffer stress-corrosion cracking in service, and they can fail via fatigue. When they break they usually snap in the male part of the bolt such that the head pops off.
If you are sure that the bolts backed out (rather than broke) you could try higher strength (eg red) threadlock instead. This will still come apart with normal hand tools in most cases and if necessary it can be degraded by heat. However I would say that normally the bolts would only back themselves out if they were not tight enough to start with, and threadlock prevents bolts from being retightened (eg should any settling occur).
If the bolts are in fact breaking, I'd suggest that you use different bolts, e.g. made in stainless steel or something.
BTW to work satisfactorily, it is important that chainring bolts retain a fair amount of tension in them. Without this the chainrings are typically on the move all the time. I don't use threadlock on my chainring bolts, because it isn't unusual for the joint to settle slightly after a short period of use (with new parts) such that the bolts need to be retightened. With parts that have been together before, it is less likely that the joint will settle, so the bolts will almost certainly stay tight. To make sure that the bolts tighten easily without galling (and won't seize in service), I use grease or anti-seize in the screw thread itself and (if necessary) a little under the head of the male part of the bolt too. Where the sleeve part of the bolt bears against the other parts the bolt is kept dry.
In most case the consequences of riding with a chainring bolt that is missing/not tight enough are far worse than the loss of such a bolt per se; there may be wear at the interfaces and the chainring may even fail wholesale (fold over) if it sees a very high load and the bolt is missing.
So I'd suggest that -if it isn't clear already- you need to identify what is really going on and act accordingly.
hth
cheers
IIRC these bolts are of conventional type but made in aluminium and use a torx fitting.
Blue thread lock works as a lubricant as the bolt is tightened but then acts to prevent the male part and the female part from unscrewing from one another. The stuff can be pre-applied as a paste which contains micro-capsules; the micro-capsules burst under pressure and release the locking agent. IMHO it is extremely unlikely that the male part of the bolt would be able to back itself out five turns or so without you noticing that something is wrong, if the threadlock is properly applied.
You say that the bolts come undone; if you find one half of the bolt remaining in the crankset this seems likely. However if you don't find either half of the missing bolt, I'd suggest that it is also possible (likely in fact) that the bolt has simply broken and both halves have dropped out.
As a general rule I don't like aluminium chainring bolts; they gall as they are tightened (unless copiously lubricated), they suffer stress-corrosion cracking in service, and they can fail via fatigue. When they break they usually snap in the male part of the bolt such that the head pops off.
If you are sure that the bolts backed out (rather than broke) you could try higher strength (eg red) threadlock instead. This will still come apart with normal hand tools in most cases and if necessary it can be degraded by heat. However I would say that normally the bolts would only back themselves out if they were not tight enough to start with, and threadlock prevents bolts from being retightened (eg should any settling occur).
If the bolts are in fact breaking, I'd suggest that you use different bolts, e.g. made in stainless steel or something.
BTW to work satisfactorily, it is important that chainring bolts retain a fair amount of tension in them. Without this the chainrings are typically on the move all the time. I don't use threadlock on my chainring bolts, because it isn't unusual for the joint to settle slightly after a short period of use (with new parts) such that the bolts need to be retightened. With parts that have been together before, it is less likely that the joint will settle, so the bolts will almost certainly stay tight. To make sure that the bolts tighten easily without galling (and won't seize in service), I use grease or anti-seize in the screw thread itself and (if necessary) a little under the head of the male part of the bolt too. Where the sleeve part of the bolt bears against the other parts the bolt is kept dry.
In most case the consequences of riding with a chainring bolt that is missing/not tight enough are far worse than the loss of such a bolt per se; there may be wear at the interfaces and the chainring may even fail wholesale (fold over) if it sees a very high load and the bolt is missing.
So I'd suggest that -if it isn't clear already- you need to identify what is really going on and act accordingly.
hth
cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
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Tigerbiten
- Posts: 2525
- Joined: 29 Jun 2009, 6:49am
Re: Chainring bolts falling out
Further to Brucey's post ........
I've had chainring bolts come loose and fall out.
I don't think they were tight enough as I didn't have a chainring screwdriver at the time.
The nuts were dropping off as I only had 2 nuts and 4 bolts (out of 5) when I noticed it was happening.
The next set I used blue Loctite on them as I tightened them up.
They must all have worked loose by around 1/4 turn as the chainrings were loose on the spider 5 years later.
But I needed a chainring screwdriver and allen key to separate the bolt from the nut.
I've had chainring bolts come loose and fall out.
I don't think they were tight enough as I didn't have a chainring screwdriver at the time.
The nuts were dropping off as I only had 2 nuts and 4 bolts (out of 5) when I noticed it was happening.
The next set I used blue Loctite on them as I tightened them up.
They must all have worked loose by around 1/4 turn as the chainrings were loose on the spider 5 years later.
But I needed a chainring screwdriver and allen key to separate the bolt from the nut.
Re: Chainring bolts falling out
FWIW if you
a) follow the recipe above (in the para starting 'BTW' in my earlier post) and
b) retighten the bolts after a few hundred miles
then it is extremely unlikely that the chainring bolts will give any trouble in service or be difficult to undo. It is also extremely unlikely that you will need a tool to hold the female part of the bolt when either retightening or loosening the bolts. This is the whole point of using a fine pitch thread in these bolts.
I am told that these days, engineering students are often taught that fine pitch bolts are no better than coarse pitch bolts when it comes to keeping things nice and snug. Maybe it is true in some cases, but engineers from earlier generations wouldn't believe it for a moment. It would have been very easy to use coarse standard Whitworth threading on bicycle parts but the designs soon (i.e. about 110 years ago) settled on relatively fine threads (24tpi, 26tpi etc) but not so fine that they would instantly strip with a little wear or have excessively demanding manufacturing tolerances.
[BTW I think that the 20tpi pedal thread may have arisen because a finer thread might precess (i.e. self-tighten) too much and make the pedals difficult to remove, whilst also being more likely to strip, but I don't know this for sure.]
Chainring bolts usually have an M8 x 0.75mm thread in them (i.e. it is about 34tpi) which is easily the finest pitch thread in any commonly used structural bike part. [Actually I can think of one other thread that is finer than this, but it doesn't appear on every bike and most folk that have it don't know it is there..
.].
Bolts also need to be able to deform something, somewhere, elastically, in order to retain tension. Long bolts stretch, and thick assemblies can be inherently springy. Failing that, elastic elements like Belleville washers (disc springs) etc can keep some tension in the joint. None of that applies to a chainring bolt; I think they only work at all because the head of the male part of the bolt deforms like a disc spring. I don't know if that was intentional when the bolts were first designed, but that appears to be how they work....
cheers
a) follow the recipe above (in the para starting 'BTW' in my earlier post) and
b) retighten the bolts after a few hundred miles
then it is extremely unlikely that the chainring bolts will give any trouble in service or be difficult to undo. It is also extremely unlikely that you will need a tool to hold the female part of the bolt when either retightening or loosening the bolts. This is the whole point of using a fine pitch thread in these bolts.
I am told that these days, engineering students are often taught that fine pitch bolts are no better than coarse pitch bolts when it comes to keeping things nice and snug. Maybe it is true in some cases, but engineers from earlier generations wouldn't believe it for a moment. It would have been very easy to use coarse standard Whitworth threading on bicycle parts but the designs soon (i.e. about 110 years ago) settled on relatively fine threads (24tpi, 26tpi etc) but not so fine that they would instantly strip with a little wear or have excessively demanding manufacturing tolerances.
[BTW I think that the 20tpi pedal thread may have arisen because a finer thread might precess (i.e. self-tighten) too much and make the pedals difficult to remove, whilst also being more likely to strip, but I don't know this for sure.]
Chainring bolts usually have an M8 x 0.75mm thread in them (i.e. it is about 34tpi) which is easily the finest pitch thread in any commonly used structural bike part. [Actually I can think of one other thread that is finer than this, but it doesn't appear on every bike and most folk that have it don't know it is there..
.].Bolts also need to be able to deform something, somewhere, elastically, in order to retain tension. Long bolts stretch, and thick assemblies can be inherently springy. Failing that, elastic elements like Belleville washers (disc springs) etc can keep some tension in the joint. None of that applies to a chainring bolt; I think they only work at all because the head of the male part of the bolt deforms like a disc spring. I don't know if that was intentional when the bolts were first designed, but that appears to be how they work....
cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
Re: Chainring bolts falling out
Actually I can think of one other thread that is finer than this, but it doesn't appear on every bike and most folk that have it don't know it is there.
Oh you tease! The thread on a freewheel is pretty fine but I guess not finer than that....
Re: Chainring bolts falling out
Thanks to Brucey & Tigerbitten - I'll investigate more tomorrow. I am a novice at this sort of stuff ( could you tell?) The LBS sourced Campag bolts ( approx £30 for 4). Both parts have dropped out on every occasion. It didn't feel a great fit initially, so perhaps some distortion of the spider/chainring has already taken place.
Will revert anon.
Best
Chesters
Will revert anon.
Best
Chesters
Re: Chainring bolts falling out
Chesters wrote:Thanks to Brucey & Tigerbitten - I'll investigate more tomorrow. I am a novice at this sort of stuff ( could you tell?) The LBS sourced Campag bolts ( approx £30 for 4). Both parts have dropped out on every occasion. It didn't feel a great fit initially, so perhaps some distortion of the spider/chainring has already taken place.
Will revert anon.
Best
Chesters
I assume you are talking a bout the new style chainsets with 4-arm? Or it was the older type with 5-arms of which one is under the crank?
Those bolts do not fall by themselves unless is the "hidden" one under the crank, that can give problems though the use of medium Loctite does always cure the problem.
It is by riding a bicycle that you learn the contours of a country best,
since you have to sweat up the hills and coast down them.
Thus you remember them as they actually are...
since you have to sweat up the hills and coast down them.
Thus you remember them as they actually are...
Re: Chainring bolts falling out
Used the best "biting" of my 2 remaining bolts and covered in Loctite 243 ( medium strength). One modest 2 hour ride and it is still in place... time will tell...
Re: Chainring bolts falling out
Brucey wrote:It is also extremely unlikely that you will need a tool to hold the female part of the bolt when either retightening or loosening the bolts.
I've found with a couple of chainsets that had one, or more, bolts that wouldn't tighten fully without a tool on the nut side - beyond a certain tightness the nut would just start to rotate. I never took the time to figure out if it was a particular bolt, nut or chainset position (or a combination) that was the cause. The proper tool means that I can always do all bolts up tight at home. Out on the road I have almost never had to do any loosening or tightening of chainring bolts - I can only recall one time in over 40 years.
Former member of the Cult of the Polystyrene Head Carbuncle.
Re: Chainring bolts falling out
it only takes a tiny piece of crud in the threads or binding to upset the delicate balance. New bolts are clean, so greasing the threads is usually good enough. But used bolts are often dirty, and occasionally this causes a problem.
For this reason, with used bolts, it is best to grease the two halves, run them all the way into one another (to make sure they won't bind), then separate the two halves, and then fit them to the chainset. This way they will always tighten OK without the use of a tool on the female part. They will also separate OK, too.
cheers
For this reason, with used bolts, it is best to grease the two halves, run them all the way into one another (to make sure they won't bind), then separate the two halves, and then fit them to the chainset. This way they will always tighten OK without the use of a tool on the female part. They will also separate OK, too.
cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~