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Query re chainring replacement

(13 posts)
  • Started 9 years ago by Mandopicker101
  • Latest reply from Mandopicker101

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  1. Mandopicker101
    Member

    In a bid to try and get my bike of the sick-list, I'm minded to attempt replacing the worn inner ring, which I believe to be part culprit for a 'drrr-thwick' noise when pedalling under load. Doesn't happen on the less worn outer ring and, looking at the inner ring, it's got pointier teeth than a roomful of vampires (only other cause might be stiffness in the Missing Link in the chain).

    The bike has a 105 Hollowtech crankset (Octalink BB). Reference to the Park Tools site suggests I have self-extracting cranks, which require an allen key to, er, extract. The Big ring is in good nick.

    My read of the various how-to guides is:

    'Remove crank, remove chainset, unscrew dud chainring, fit new chainring etc...'

    Without wishing to seem unduly thick...is that it?

    Posted 9 years ago #

  2. Wilmington's Cow
    Member

    Pretty much. Just make sure the new chain ring is the same number of bolt holes and spacing between them!

    Posted 9 years ago #

  3. le_soigneur
    Member

    Assuming you've got the correct replacement...
    1. Turn the new one the right way around if it is dished
    2. Don't forget to put the chain on before tightening the pedal onto octalink.
    Sounds obvious, but could save you from a schoolboy error.

    Posted 9 years ago #

  4. Mandopicker101
    Member

    Thanks all - OK now I'm nervous. This is, like, real bike doctoring stuff. <Gulps>

    Chainring to be bought tomorrow then. It'll be nice to have a mostly silent bike again. Presumably greasing the bolts I remove is a Good Thing? I have marine grease in the shed.

    Posted 9 years ago #

  5. kaputnik
    Moderator

    the same number of bolt holes and spacing between them

    The measure is called Between Centres (or Bolt Centre) Diameter, often just BCD. So 146BCD = 146mm measurement.

    Wipe down and regrease the bolts, yes. The chainring bolts are a threaded male part which fits in a matching threaded female part. There's a slot on the female part to stop the whole lot spinning as you tighten them up, you can get a little wrench specifically for this, but generally a 5p piece or washer will do the job, once you get some tension in it it will usually stop spinning.

    Oh, one last thing, you don't necessarily need the same amount of teeth on the new ring, you could use less to give you a little bit more gearing, or more if you spin out to easily on the small ring. The Shimano technical documents for your derailleur on their website will tell you minimum/maximum number of teeth you can get away with.

    Shimano try to confuse by insisting you match A-type chainrings to A-type chainrings and B to B etc. Ignore this, it doesn't really matter, I've been told on good authority the shifting difference is almost imperceptible.

    Last thing, don't go for a bargain basement chainring with no ramps milled into the teeth, it will make shifting clunky.

    Posted 9 years ago #

  6. chdot
    Admin

    http://www.sheldonbrown.com/cribsheet-bcd.html

    Posted 9 years ago #

  7. Cyclingmollie
    Member

    You can replace the chainring without removing the cranks. Just take off the chain, undo the chainring bolts and the rings will come off.

    Posted 9 years ago #

  8. kaputnik
    Moderator

    @cyclingmollie I can't see how that would work on an inner chainring? How do you get the old one off and the new one on over the spider arm, never mind the crank arm itself?

    Posted 9 years ago #

  9. Cyclingmollie
    Member

    There's plenty of clearance.

    Posted 9 years ago #

  10. Wilmington's Cow
    Member

    You'd have to take the large chainring off as well, but yeah, it's then a wiggle over the spider.

    Posted 9 years ago #

  11. kaputnik
    Moderator

    Well I never. Eyed up my bike with a double on it and it might just work!

    The triple however is another story...

    Man in the orthopaedic shoes, etc.

    Posted 9 years ago #

  12. threefromleith
    Member

    I took the crank off to replace a chainring two weeks ago. Mind you, it was the middle ring of my Tiagra triple - but it's good to take everything off so you can easily clean off all the caked-on crud that's built up in hard-to-reach nooks & crannies!

    Posted 9 years ago #

  13. Mandopicker101
    Member

    ...and of course no-one locally has a 39T chainring in 130BCD. LBS might be able to rustle one up tomorrow, but I guess one more day with the worn ring won't totally kill the chain....will it?

    Posted 9 years ago #

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