Front Mech

Wamas
Wamas Posts: 256
edited December 2012 in Workshop
Okay, not a new question and one I have fixed before, but just cant remember how I did it.

I fitted a new set of cranks, had to adjust the height of the front band-on mech and now the front mech overshoots dropping the chain when shifting up to the big ring when I am on the smaller end of the cassette at the back.

The front derailleur is parallel to the large chainring at the front, and the high screw is screwed in as far as it can go still leaving quite a consdiderable gap between the outer plate and the chain (3mm instead of 1mm).
Do I tail in or tail out the front derailleur to stop this happening?

Thanks.

Comments

  • nicklouse
    nicklouse Posts: 50,675
    did you reposition the cable?

    read how instal and set up front mechs on Parktools.
    "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
    The front mech plates need to be parallel to the chainset so do not toe in or out.

    If the limit screws do not adjust it sufficiently and it is cabled correctly the new chainset must have a longer spindle and you will not make it fit.
    Yellow is the new Black.
  • onbike 1939
    onbike 1939 Posts: 708
    If it is the "H" screw that is screwed tightly in and not the "L", (this happens) then it does sound as if the spindle is too long and the chain-line is out. If your new chain-set is of the tapered BB variety then a shorter BB is needed. If the chain-set is the newer two part type, then this is more problematic.
    Measure your chain-line to check this.

    http://sheldonbrown.com/chainline.html
  • Wamas
    Wamas Posts: 256
    Thanks for comments.

    Yes I have repositioned the cable, I was changing from a compact to a double, so I repositioned the height of the front mech, I adjusted the cable, adjusted both the low and the high limit switches, and I didn't make a mistake between the two. I have fitted a few front mechs and chainsets before.

    The chainset in question was a shimano 7800 with stronglight chainrings which I fitted to my winter bike (allez) with a 7900 BB correctly sized and fited to the bike.

    All I can think of is that the 7800 chainrings normally flare out slightly, whereas the stronglight chainrings are totally flat.

    Anyway, I tailed in the front mech slightly and still allows for perfect shifting and now doesn't try to overshift the chain on the large ring. Problem solved.

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