Chainset broken

BobScarle
BobScarle Posts: 282
edited April 2014 in Workshop
My Bianchi came with an FSA Gossamer chainset. From the start I have had a problem with the centre cover unscrewing. Today I thought I would have another look and maybe put some locktight on the thread. I unscrewed the cover, removed the crank and this is what I saw.



The axle has a lump broken off. In fact the missing piece is inside the crank, if you scroll down and look carefully you can see it. My question is, how can this have happened? Is it possible that the pinch bolts have been overtightened? Is it metal fatigue? Or maybe something else? I am at a loss to explain it. I don't have a torque wrench, but I may be buying one now.

Can anybody offer any suggestions?
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Comments

  • dennisn
    dennisn Posts: 10,601
    About the only thing I can offer is that sometimes things break. Not sure if you will ever know whether it was metal fatigue(although something obviously fatigued) or faulty manufacturing or over tightened bolts or poor design or some other problem.
  • pinno
    pinno Posts: 52,326
    Ouch !
    seanoconn - gruagach craic!
  • BobScarle
    BobScarle Posts: 282
    I know that sometimes parts fail, seemingly for no reason. But I would like to find out why in order to avoid a repeat. I have been able to find 1 report on the net of an FSA Gossamer breaking. It cannot be a common failure.
    pinarello001 wrote:
    Ouch !
    I didn't know about the failure until I took the crank off. Not sure how long it had been like that or what could have happened. New chainset and bottom bracket (might as well) ordered from Wiggle.
  • ugo.santalucia
    ugo.santalucia Posts: 28,312
    BobScarle wrote:
    Can anybody offer any suggestions?

    What exactly are you asking? It seems obvious that's good for the bin... are you asking how to remove it?
    left the forum March 2023
  • BobScarle
    BobScarle Posts: 282
    ugo.santalucia wrote:
    BobScarle wrote:
    Can anybody offer any suggestions?

    What exactly are you asking? It seems obvious that's good for the bin... are you asking how to remove it?
    No, not at all. I thought I made it pretty clear that I was asking how it may have happened. I cannot explain it and I asked to see if anybody else could or at least offer a suggestion. It is going in the bin.

    I have removed the chainset and bottom bracket, just waiting for the new one to arrive from Wiggle.
  • ugo.santalucia
    ugo.santalucia Posts: 28,312
    90% of metal failures are down to fatigue, the rest is either bad design or bad quality control/manufacturing
    left the forum March 2023
  • dgunthor
    dgunthor Posts: 644
    can't tell from the picture, but thought the chainset might be ok and just replace the B/B?
  • BobScarle
    BobScarle Posts: 282
    The axle of the chainset has a lump missing out of it where the left crank arm fits. It needs to be replaced. The bottom bracket is ok as far as I know but I am going to replace it whilst I have it all stripped down (seems daft not to).
  • dgunthor
    dgunthor Posts: 644
    my bad, thought the axle was part of the BB
  • balthazar
    balthazar Posts: 1,565
    If you can take a good sharp well lit photograph of the actual failure point, you might be able to determine where the crack started. Fatigue failures are usually fairly easy to analyse- their history is written like growth rings in cut trees. Have a look at some examples on this page:

    http://pardo.net/bike/pic/fail-009/000.html
  • BobScarle
    BobScarle Posts: 282
    This is about the best I can do with my camera. I have had a close look at the failure and cannot see any noticeably darker areas that might indicate an older split. If it turns out to be "Just one of those things" then so be it. I will not worry too much, unless of course my new one also fails.

  • balthazar
    balthazar Posts: 1,565
    It's not easy getting that close-up, is it?! It still isn't really enough to work out exactly how the failure developed, but there are enough sharp corners in that axle it could have started anywhere.

    This is largely academic interest, though: I think your query was already answered by others- stuff breaks occasionally. This axle doesn't seem particularly more vulnerable than any number of other bike parts. Cleverer, more thoughtful design could undoubtedly improve durability enormously in bike components, but that's something for another world, I think- one where durability is generally rated higher than low weight and novelty.
  • slowbike
    slowbike Posts: 8,498
    I'm struggling to work out how it could fracture like that ...
    The pressure from the crank arm will be rotational against the splines and should be equal across all of them.
    Was the bit that fractured off the bit that located the crank arm in the right place?
  • BobScarle
    BobScarle Posts: 282
    Slowbike wrote:
    Was the bit that fractured off the bit that located the crank arm in the right place?

    If I understand you correctly, yes it was. The pinch bolts are in the middle of the broken part. Now I am not sure if that is relevant or not, but it is the reason I asked about overtightening.
  • pirnie
    pirnie Posts: 242
    Yes, stuff breaks. But I'm surprised no one has mentioned warranties yet. How old was this chainset?
  • BobScarle
    BobScarle Posts: 282
    The chainset is about 3 years old so probably out of warranty. However I did think about sending it to FSA for them to look at and comment on. Not after a replacement just thought it might help them.
  • Wirral_paul
    Wirral_paul Posts: 2,476
    My best guess would be the axle end bolt may have been overtightened. Would be interested to see how deep the end bolt goes into the axle and whether the failure corresponds with that point. Nasty anyway - i guess it shows the benefit of the pinch bolt helping to keep it all in place :(
  • buckmulligan
    buckmulligan Posts: 1,031
    Is the section that has broken away directly under the pinch bolts? i.e. facing directly up when the drive side crank is pointing up? It's hard to tell from the pictures shown, but if so, you'd have to say overtightening of the pinch bolts could easily be the cause. I'd send the pics off to FSA and see what they say though.

    I always wondered why the Shimano Hollowtech splines were so shallow and numerous, perhaps it's to prevent this kind of failure.
  • mr_evil
    mr_evil Posts: 234
    Overtightening sounds plausible. This is why I would like to see more cranks with barrel nuts instead of the bolts screwing directly into the crank (like the THM Clavicula in the attached picture. Note that it also has wavy splines - no sharp edges that form stress risers). This prevents the clamping force being concentrated on the edge just below the bolts.
    https://mrevil.asvachin.eu/
  • pinno
    pinno Posts: 52,326
    @ Balthazar - yep, that different world is Campagnolo.

    @Mr Evil - at £640 !! More expensive than Super Record 11 (£475) with less tradition and history.
    seanoconn - gruagach craic!
  • BobScarle
    BobScarle Posts: 282
    Over tightening could well be the cause, I didn't use a torque wrench. I guess it is a bit of an expensive lesson.

    I went to the FSA web site and put an initial contact request to them. I would like to send the chainset off for FSA to look at and comment on. Interestingly there is a recall notice on the site. Now it is not the same as mine and doesn't apply but it does talk about failure due to over tightening. If you are interested, here's the link

    http://www.fullspeedahead.com/technews/ ... all-Notice

    I have read that torque keys are not very reliable. Can anybody confirm this and maybe recommend a suitable tool.
  • BobScarle
    BobScarle Posts: 282
    Sent the pictures to FSA UK to see what they come back with. I will post their response in due course.
  • pinno
    pinno Posts: 52,326
    BobScarle wrote:
    I have read that torque keys are not very reliable. Can anybody confirm this and maybe recommend a suitable tool.

    No. just like Alen keys in that you have to get the exact fit.
    seanoconn - gruagach craic!
  • paulbnix
    paulbnix Posts: 632
    I have the same FSA Gossamer MegaExo on my bike (hopefully its still ok).

    I saw that Planet X were selling the FSA Gossamer chainset and a MegaExo BB for £44 so I ordered one as a spare.
    The new one does not have the same attachment mechanism for the nds crank and looks like below.

    I wonder if they have changed the design because of issues.


  • BobScarle
    BobScarle Posts: 282
    That's interesting, thanks Paul. It may be because of problems that they have changed although I would have expected to find more on a search. I have emailed the pictures to FSA and they have asked me to send them the chainset, which of course I will.

    New 105 chainset and bottom bracket has just arrived from Wiggle. I think I may end up buying a torque wrench before I fit them.
  • buckmulligan
    buckmulligan Posts: 1,031
    I've got one of these:

    http://www.amazon.co.uk/gp/product/B000 ... sc=1&s=diy

    Cheap and does the job well, only goes down to 10Nm, but anything less than that just do gently by hand.
  • paulbnix
    paulbnix Posts: 632
    I have got a similar cheap torque wrench and they seem fine but don't come with any hex or socket bits. You can get them from EBay or Machine Mart.
  • paul_onabike
    paul_onabike Posts: 194
    I wish that I had not read this post :(

    I have just examined my power meter cranks which are FSA Gossamer megaexo crank arms, and I too have found a crack :( .
    The cranks are only one year old, and have always been tightened using a torque wrench. There is obviously a design flaw, and I have contacted the supplier of the cranks. At this time I am still awaiting a reply.

    I would suggest that you all check your cranks before failure causes an crash.
  • balthazar
    balthazar Posts: 1,565
    Paul Onabike wrote:
    I wish that I had not read this post :(

    I have just examined my power meter cranks which are FSA Gossamer megaexo crank arms, and I too have found a crack :( .
    The cranks are only one year old, and have always been tightened using a torque wrench. There is obviously a design flaw, and I have contacted the supplier of the cranks. At this time I am still awaiting a reply.

    I would suggest that you all check your cranks before failure causes an crash.

    It looks to me that the crack started exactly where you'd expect it to- at the base of the spline, where there is a sharp corner. The newer version shown above is designed such that this stress-raiser doesn't exist.
  • BobScarle
    BobScarle Posts: 282
    That really is worrying. I thought my failure may just be a one off due to poor installation on my part. I might have to rethink that now. I have just finished wrapping up the chainset ready to send back to FSA. I will post their response here in due course.

    Paul. Just think. If you hadn't have read this thread, you would not have looked for that crack. You may only have become aware of it when it failed.

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