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why does my chain keep jumping of the chainset?

TrailradarTrailradar Posts: 131
edited December 2009 in The workshop
my chain when cycling along keeps jumping off slightly on the smaller chain rings on the chainset. I have inspected the teeth on the chain set but all seem okay. I was going to attempt to adjust the screws on the rear mech' but it is okay on the smallest ring - so if I adjusted it their then it might actually fully jump off the chainset and get caught betwen the chainset and lower frame.

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  • Either your rear mech needs reindexing or your chain and cassette are worn and need replacing. LBS visit required; fiddling around with rear mech screws if you're not sure what you're doing can rarely work wonders.
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  • nicklousenicklouse Posts: 81,520 Lives Here
    so what gears does it jump off the small front cog?

    why would you want to adjust the rear mech? when the problem is at the front!

    sounds like the front mech needs adjusting.
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  • Greg66 wrote:
    Either your rear mech needs reindexing or your chain and cassette are worn and need replacing. LBS visit required; fiddling around with rear mech screws if you're not sure what you're doing can rarely work wonders.

    Chain = relatively new - less than 1yr old and bike not used all time

    casette = 1yr old bike but initial inspection seems that its not worn (is casette same as the rear chainset/ring? :oops: ) - because I am refering to the collection of rear chainrings.
  • nicklouse wrote:
    so what gears does it jump off the small front cog?

    why would you want to adjust the rear mech? when the problem is at the front!

    sounds like the front mech needs adjusting.

    The REAR chainset/ring has the problems. The 'go go hamster, sorry, faster chainrings' have the problem, the chain justs seems to pop out of place.
  • nyanzanyanza Posts: 68
    Right. So this problem has nothing at all to do with your chainset! That bit sits at the front of the drivetrain and connects to the pedals...

    The rings/cogs where the chain is slipping belong to the cassette (not chainset), at the back of the bike. Yes? And it doesn't sound like the indexing is out as it only skips on the smaller 'cogs', and the stop screw can't go any further out.

    From what you've said, sounds like it's time to change the cassette. The chain starts to skip when in the smallest 'cogs' because smaller 'cogs' wear much faster as there are fewer teeth to spread the load of the chain. The bigger 'cogs' will wear slower hence they are not skipping. The smaller teeth may not look worn, but they may well be. Feel the tops of the teeth with your fingertips and they might have a slight and sharp hook that you can't immediately see - they're the worn teeth.

    You'll probably need a new chain as well, but change the cassette first and see how you go. As the chain is so new it might not have worn at all so it could well fit the new cassette. At the slightest hint of something not feeling right then change the chain, because running a worn chain on a new cassette will wear out both parts super quick and cost more in the long run.
  • iain_jiain_j Posts: 1,941
    nyanza wrote:
    From what you've said, sounds like it's time to change the cassette.

    Wouldn't have thought so at just 1 year old :?

    Could be the indexing, like you say no point adjusting the stop screws, because they'll only affect the chain falling off the largest/smallest sprockets. Have a play with the barrel adjuster where the cable goes into the rear mech - I'm never sure which way round this is but let's see ... turning it anti-clockwise increases the cable tension, pulling the chain "up" onto the larger sprockets ... so if the chain is falling "down" onto the smaller ones, this is what you want to be doing.

    Only adjust it by a quarter-turn at a time and then change up and down through the gears a few times to test it.
  • nyanzanyanza Posts: 68
    Wouldn't have thought so at just 1 year old
    A few weeks ago I'd have agreed with you there completely. But I personally just changed a worn cassette after only 4 months and only around 700(!) miles of commuting. I simply couldn't believe it would wear that quick, but it certainly and visibly did. Cheap Shimano; and White Lightening lube - never again.

    One giveaway for cassette wear would be this:
    -Does the chain skip when you get out of the saddle and go down hard on the pedals = worn cassette
    -Is it skipping when you just pootle along as well with no real force or tension on the chain = play with the index barrel just as iain_j suggests
  • iain_jiain_j Posts: 1,941
    nyanza wrote:
    A few weeks ago I'd have agreed with you there completely. But I personally just changed a worn cassette after only 4 months and only around 700(!) miles of commuting. I simply couldn't believe it would wear that quick, but it certainly and visibly did. Cheap Shimano; and White Lightening lube - never again.

    Blinkin' eck - what was it made of - plastic?
  • nyanzanyanza Posts: 68
    Tell me about it. Either the cassette was rubbish, or my computer can't count miles. It was only the 11t sprocket that wore out, but I use that all the time. I've just replaced the freehub body, as it was slightly loose. I can only assume the tiny wobble in that sped up the erosion!!?
  • Benno68Benno68 Posts: 1,689
    I agree with Ian J that the cable needs adjusting, at least this simple adjustment is worth a try first of all. Depends on the people in your LBS, but the guys in my LBS adjusted mine and showed me how to do it for free - mind you I do spend a few quid there!

    This link shows how to adjust the cable tension to the rear deraillure:

    http://www.wonderhowto.com/how-to/video/how-to-adjust-a-rear-derailleur-173239/

    Hey Nyanza - you say you use the 11t all the time, not crossing the chain line too much are you? If you're in he 11t and you're in the small chainring, that'll accelerate the wear, should last well beyond 700 miles, unless your Mark Cavendish :)
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