Issue with rear mech and chain?

edhaslam
edhaslam Posts: 29
edited July 2013 in Road beginners
I recently purchased a new bike after getting back into cycling, however whilst cleaning the chain with the chain on the bigger chainwheel cog and the uppper sprocket cog the other day, I noticed a problem with the rear derailleur/mech. If I select the highest chainwheel cog and the lowest (biggest in size) gear on the rear sprocket, then the rear mech seems to be over extended, as in the image below. So much so that it is making an odd noise. I understand that cross-chaining is a bad thing and that this combination of gears shouldn't really be used, but even if I drop the sprocket gears down one or two cogs, the rear mech is still over extended. It's as if the chain is too short (this is how it was supplied to me). Is this normal behavior? I'm assuming the chain is at an angle in this gear combination and is rubbing on the rear mech cage, hence the noise that can be heard. I guess the question is, is this normal behaviour? Is this an indication of the chain being too short regardless of the (incorrect) use of the big-big cogs being used? Running an SLK compact chainset and a Shimano Ultegra 11-28 sprocket. Any advice would be useful, cheers.

image.jpeg
image1.jpeg

Comments

  • drlodge
    drlodge Posts: 4,826
    Can you post a photo of the chain in the small-small combination? That will show whether the chain is too short, or the rear derailleur has insufficient capacity.
    WyndyMilla Massive Attack | Rourke 953 | Condor Italia 531 Pro | Boardman CX Pro | DT Swiss RR440 Tubeless Wheels
    Find me on Strava
  • edhaslam
    edhaslam Posts: 29
    No probs, will grab a shot when I get home.
  • nicklouse
    nicklouse Posts: 50,675
    that chain looks fine. and as you say you never us it like that.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • smidsy
    smidsy Posts: 5,273
    Rear mech capacity is fine for compact + 11/28, I have this very combination.

    I would question the rear mechs general position (it is easy to install them wrong).

    Need to see a picture with the chain in small front/large rear to be sure.

    Also I would say the chain may well be too short (but need the other picture to be sure).
    Yellow is the new Black.
  • edhaslam
    edhaslam Posts: 29
    nicklouse wrote:
    that chain looks fine. and as you say you never us it like that.

    That's good to hear, thanks. It still find it odd that we have 20 gears, yet a good proportion of them cannot be used (in certain combinations). I guess things have changed a lot since I rode as a kid!
    drlodge wrote:
    Can you post a photo of the chain in the small-small combination? That will show whether the chain is too short, or the rear derailleur has insufficient capacity.

    Here's a couple of it in the small-small gears:

    image-1.jpeg

    image1-1.jpeg
  • edhaslam
    edhaslam Posts: 29
    smidsy wrote:
    Need to see a picture with the chain in small front/large rear to be sure.

    Also I would say the chain may well be too short (but need the other picture to be sure).

    I'll see what I can do Smidsy...
  • edhaslam
    edhaslam Posts: 29
    Here's a couple of small-front/large rear, so to speak!

    image2.jpeg

    image3.jpeg
  • smidsy
    smidsy Posts: 5,273
    Actually general mech position looks ok.

    However, IMO the mech is a little too close to the cassette and could do with the B-screw adjusting (2 links is about right). The chain length for me is a little short too (by 3 links or so).

    But this is bound to meet with constenation amongst the masses :-)
    Yellow is the new Black.
  • Wirral_paul
    Wirral_paul Posts: 2,476
    Chain looks spot on for length - small / small shows it correct.

    Can you see where the chain rubs on the mech in large / large combo? Makes me wonder if the backplate of the mech cage has been fitted upside down if it has been disassembled at some stage.
  • edhaslam
    edhaslam Posts: 29
    On closer inspection I think the noise is coming from the chain sort of plinking off the bottom pulley when in the big-big gear. If you rotate the chain wheel slowly you can hear each link pinging off the teeth of the pulley. I imaging the angle of the chain is preventing it to run square across the teeth of the cog? It's still pretty close to the cage near the top pulley though.
  • jgsi
    jgsi Posts: 5,062
    Put it in big chainring / smallest sprocket and get behind the bike.
    The chain line from the small cog down to the pulleys should be nice and aligned.
    If it is not then you need to adjust or have someone adjust the rear mech to get chain running smoothly in this combination. AN easy job but not if you havent done it before.
  • smidsy
    smidsy Posts: 5,273
    Also make sure the chain is routed properly through the mech. There is a little guide/lug between the two jockey wheels that the chain needs to go through. Get it wrong and you get noisy running.
    Yellow is the new Black.
  • edhaslam
    edhaslam Posts: 29
    Ok great. Thanks for the tips, I'll have a go at setting it up tomorrow. Will let you know how I get on.

Categories