Help! Inner chainring gouging frame!

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  • Help! Inner chainring gouging frame!
  • Tom Zesty
    Member

    After fettling my bike upside down just noticed that the bottom of the frames been gouged (rubbed off paint and scratched into metal). Looks to me like its the inner chainring thats done it, but its standard – I haven’t changed it, messed with it and theres no play in the bottom bracket. Anyone else had this? Can I alter anything or do I need a new chainring? Cheers, Tom.

    Edric 64
    Member

    Are the spacers in the right place?

    belugabob
    Member

    This is probably caused by ‘chain suck’ – this is where the chain temporarily gets caught between the inner ring and the frame. Quite often, when you stop pedalling, this situation resolves itself and, if it happens several times, your frame will look like you describe.
    I should imagine that most well used bikes will exhibit this to some degree.

    Tom Zesty
    Member

    Don’t think its the chain, its a thin groove that matches the metal lugs behind the bolt holes on the inside of the chainring, and when you pedal it I can see contact. I’ve noticed that higher end inner chainrings, like XT and Saint, dont have that metal lugs behind the bolts so it could be the design.

    belugabob
    Member

    Peddling + contact = worrying condition – how old is the bike?

    jimmyjames
    Member

    Are the bolts tight?

    ojom
    Member

    Presuming from your name you might be on a Zesty. Check your pivot bearings. You might have play that is causing this. Seen it before.

    Tom Zesty
    Member

    Yeah its a 2010 zesty, basic model. There’s no play in the suspension or the bb. It looks like a slightly too small chainring has been fitted. I’ll check all the bolts tomorrow but its not long since I checked thm. If not I’ll have take off the cranks. Thanks anyway guys, I’ll probably be back with more problems soon!

    belugabob
    Member

    Why would a smaller than normal chain ring cause this?
    If anything, it would be less likely to cause rubbing – surely?
    Pictures please.

    Premier Icon firestarter
    Subscriber

    I’ve had this with a deore inner ring as the tabs were bigger on it I swapped for an xt which has smaller more rounded tabs and it sorted it

    Tom Zesty
    Member

    Firestarter that sounds about right, just been looking on chain reaction and the xt one looks like it would sort it. Dont know why they would spec one that causes problems though, surely this must happen a lot!?

    rhys
    Member

    I may be wrong but this has been a feature of lapierres, mates spicy did the same. I seem to recall that Lapierre resolved it by speccing custom shimano inner rings without the tabs

    B.A.Nana
    Member

    Not a Zesty, but a Cube Stereo. Also, I haven’t quite understood the problem you are having, so this might be completely unrelated, but possibly worth you knowing.
    I discovered that the granny ring is not symmetrical, even tho it might look it. I had a problem with the Granny ring catching the suspension pivot on my Stereo, took the granny ring off, turned it around, put it back on, problem solved. Sorry if this is of no help.

    Skyline-GTR
    Member

    If it’s a Deore (m510 ring it’s designed for the old octalink BB design.
    But more recent M532 versions are fitted to the HTII versions of the cranks. They have more rounded tabs like the LX m580 SLX M660 ad XT M760 and 770 versions. (OE versions differ vastly from one another though)
    The only reason I can think of for lapierre fitting a 510 ring is that with the press fit BB they assumed the narrower BB would offer enough clearance in the same way the octalink does, unlike the external mounted bearings on HTII.
    Then a bit of grit gets in, and it’s ground out the shell.
    Also, the ring isn’t supprted by the tabs, so it can slip under load into an eccentric position if the bolt holes are a little oversized and one tab will make contact as it spins round.

    nickegg
    Member

    Skyline has it. Due to the extra material around the BB shell (to take the press-fit BB) Lapierre specify their chainsets with slightly different innner rings as ‘normal’ inner rings are designed for clearance around BB cups.

    Skyline-GTR
    Member

    apologies forthe late edit, (call of nature) but it might explain the contact the OP is reporting.

    Tom Zesty
    Member

    This seems to make sense – everything matches with the problem I’ve got. So my options are to try switching the chainring round then if not buy a new one?
    Certainly not riding it again til i’ve changed something theres already a fair scratch!

    ojom
    Member

    Ah my apologies I misunderstood. They do this. Mine did it. It’s a grit and tab issue.
    Either grind tabs or replace ring. Not ideal but it is what it is.

    Tom Zesty
    Member

    Ok cheers I’ll get on to it!

    Tom Zesty
    Member

    Having strode purposefully to the garage after following this thread I realised I haven’t a clue how to remove the cranks/ chainrings on a Lapierre – all the fittings are totally alien compared with my old Scott hardtail. How do I get the thing off!? (thought I’d ask the resident bike gurus on here rather than start faffing round not knowing what I’m doing!) Cheers. Don’t understand these press-fit bottom brackets either!

    spooky_b329
    Member

    My gf’s 2008 Zesty did this. We did two gritty rides and just thought the scraping sound was due to the conditions. Afterwards we noticed the damage, but by then the chainring had created its clearance. Mentioned it to the dealer but it would have meant returning the bike and a long wait as they were out of stock, and we had a guided mtb holiday booked so just took it on the chin.

    Been fine since, just cosmetic damage.

    The press fit BB can be drifted out with a mallet and socket on an extension bar, it needs a headset press (homemade threaded rod with washers works fine) to refit. However, to replace the rings you only need to remove the cranks and that involves loosening the pinch bolts and then using a HTII remover to undo the plastic nut on the non-driveside. Remove crank and then use aforementioned mallet to persuade the BB out of the shell.

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