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  1. #1
    Senior Member
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    Replaced crankset, do I need a new fd?

    I've recently replaced the crankset on my old falcon olympic with a shimano rsx 52, 42t but the chainrings are too far from the front derailleur. I bought the crankset off of ebay and it came with a shimano un52 bb, which I currently haven't installed. If I fit the matching bb will it bring the chainrings in line with the fd or will I have to replace it? The bike currently has suntour dt shifters and a 'compe-V' front mech. If i replace the derailleur will i need to change the shifters as well? Are there any adjustments I can make to my current fd so it's further from the frame? Anybody know of any cheap and compatible fds if i do need to get a new one?
    Thanks in advance!

  2. #2
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    Different cranksets sometimes do require different bottom bracket spindle lengths. It's possible -- though I don't know -- that the RSX crankset needs a shorter BB spindle than is currently on your bike. If the UN52 has a shorter spindle than your current bottom bracket, then I'd put it on the bike and see if that solves your problem. Also, have you checked the limit screws on the derailleur? If the outer limit screw isn't properly adjusted, it could be preventing your derailleur cage from swinging out as far as it needs to. I'm guessing that your problem is either the BB or the limit screw. I wouldn't think about replacing the derailleur until you've checked those things out.
    Steve

  3. #3
    Constant tinkerer FastJake's Avatar
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    If the BB included with your new crankset is shorter, install it. That should fix your problem. You want the chainrings to be in the proper position or else your chainline will be bad in many of the gears when using the big ring.
    Why "derailer" is the correct way to spell the gear-change mechanism: sheldonbrown.com/derailer.html

  4. #4
    Elitist Troglodyte DMF's Avatar
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    Quote Originally Posted by martyn3200 View Post
    the chainrings are too far from the front derailleur.
    Too far in which direction? vertically or laterally? How big were your old chain rings?
    Stupidity got us into this mess - why can't it get us out?

    - Will Rogers

  5. #5
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    My previous chainrings were 52, 40t. The derailleur is laterally too far from the chainrings. The UN52 does have a slightly shorter spindle by the look of it so I'm going to have my lbs fit it tomorrow (hopefully)...too many different tools to bother myself! Hopefully that will bring the chainrings within the fds reaching distance perhaps with some lower limit adjustment on the fd.
    I'll post again tomorrow if I get the bb replaced as I'm sure I'll have run into another problem!

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