chain falling off

chatlow
chatlow Posts: 849
edited February 2014 in Workshop
Ever since replacing a 36t with a 34t chainring and a 12-25 with a 11-30 cassette, my chain keeps falling off when going from big ring to small ring. I've tried playing around with the inner limit screw and making sure it's as close to the chain without touching it. The only problem with this is that the chain appears to move in and out a few mm (towards and away from the FD) on every revolution. Don't know what's causing this or if it's normal but I'm sure my summer bike doesn't do it. I've set the limit to a 1mm gap when chain is at its closest.

Comments

  • rolf_f
    rolf_f Posts: 16,015
    The chain is moving towards and away from the rear derailleur? Not the front? If it was the front you could take the chain off and spin the cranks to see if the chainrings are not distorted but I can't work out how the chain can move relative to the rear derailleur given that it is captive to it via the jockey wheels.
    Faster than a tent.......
  • chatlow
    chatlow Posts: 849
    on every spin, there is noticeable side to side movement of the chain, so at one point it will be 1mm away from FD cage and the next it will be 4mm away from the cage. Not sure what's causing it, but it's difficult to adjust FD correctly.

    Apologies - noticed I wrote down RD, I meant FD. Changed it now.

    As for the chainrings - they look OK, but will check again. If I have installed the new 34 chainring the wrong way around (i remember teeth are slightly curved), then would this cause the issue?
  • Ben6899
    Ben6899 Posts: 9,686
    chatlow wrote:
    on every spin, there is noticeable side to side movement of the chain, so at one point it will be 1mm away from FD cage and the next it will be 4mm away from the cage. Not sure what's causing it, but it's difficult to adjust FD correctly.

    That snippet tells me that the chainrings are loose or the preload isn't set correctly on the BB bearings (outboard or BB30) which is allowing some 'wobble' on the chainset.
    Ben

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  • chatlow
    chatlow Posts: 849
    haven't touched the BB but it's an old winter bike so i can't rule it out. As for the chainrings - both are very tight. perhaps a video might help
  • keef66
    keef66 Posts: 13,123
    Well if the chainrings bolts are tight and the rings themselves aren't bent, that only really leaves the BB.
  • chatlow
    chatlow Posts: 849
    One last thing - I cut the chain too short initially, so it now has 2 master links in it. Could this cause problems.

    Got a feeling, I'm going to be taking it all apart this weekend
  • keef66
    keef66 Posts: 13,123
    chatlow wrote:
    One last thing - I cut the chain too short initially, so it now has 2 master links in it. Could this cause problems.

    Got a feeling, I'm going to be taking it all apart this weekend

    Two quick links on a chain is not normally cause for concern. Certainly wouldn't explain a 4mm side to side wobble!
  • chatlow
    chatlow Posts: 849
    Ok, thanks. Well the cranks feel tight and the chainring bolts definitely are.. so will have to try the crank properly and go from there.

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