Front crank not properly installed?! Offset not allowing front derailluer to shift- Mtbr.com
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  1. #1
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    Front crank not properly installed?! Offset not allowing front derailluer to shift

    Hello all.. Bike newb here and still playing with some lower priced rides.. I have a GT Aggressor 2.0 and the front derailleur cannot shift to smallest in board sprocket. I have realeased all cables and adjustment screws and the derailleur looks like it is sitting as close to the frame as it can go but it looks like the sprocket it too close to the frame.. I have a GT Aggressor also and there appears to be a 1/4 inch difference between the bikes.. so my question is.. Is it possible to install the crank with an incorrect offset? it all looks like factory parts but no matter what I do it I cannot get the derailleur to move over.. Thanks for your help!

  2. #2
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    Is this a sudden change or has it always been this way?
    What crank?
    If it is a older style BB they are available in different offsets - the bike may have the wrong one. If it's a modern crank with an external BB then there are usually spacers on the BB for offset.

  3. #3
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    THis is a used bike I got this way.. I have attempted to adjust the derailleur but it will not adjust any lower.. I am not sure it appears to be the factory shimano.. I am guessing this bike is under 10 years old..

  4. #4
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    The easiest way to notice any offset of the crankset is to see how much clearance there is between each crank and chainstay. If the clearance is equal, your cranks are centered as they should be.

    You could offset them on purpose just a little bit if that's what it takes to shift to the granny ring. Having the crankset 1-2 mm towards either side should not cause any kind of injury or discomfort. Of course you can adjust your cleats in the opposite direction (if they have sideways adjustment) if you think you must.

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  6. #6
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    Maybe the bottom bracket has been replaced by one that's too short. Loosen the chainring/crank and try to figure out how much more you need to get the gears to work properly, it'll probably only be a few mm. Then take the BB out, see what size it is and buy a longer one.

    Crank-sets are different too and need different lengths of BB so it is possible that the BB is original and the crank-set has been changed. Even if that's the case, a new BB is still the cheapest way to fix it.

  7. #7
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    Thanks for your help.. I think it was installed incorrectly because there is no room to adjust the front d down any further and it sits correctly on the second gear on the crank.. so it is going to a shop to have them tell me for sure what is going on.. Thanks for the help..

  8. #8
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    Not sure if a shop can explain it any better than mr pig did. Bottom brackets come in differet sizes with different spindle lengths, and the spindle length determines the chainline (offset). The bb spindle is too short for the particular cranks on the bike.

    To confirm, measure the chainline (offset) as diagrammed in the link I posted. It should measure 47.5 to 50mm.

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    Yea.. I measured it today and it turns out to be 44mm on a GT frame which is thicker.. So they are recommending 50mm.. Now that I have the problem identified the next step is to purchase a new crank? or is there a proper fix for this.. Thanks again for all your help

  10. #10
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    Mr Pig said that getting a new bb (bottom bracket) is cheaper if you want to use that crankset.

    When you say the gt frame is thicker, do you mean the bb shell (round thing) is longer? There are two standard sizes, 68 and 73mm. Using a 68mm bb in a 73mm shell?

  11. #11
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    If you Google the part number on the crank set you should be able to find the right BB for it. I had to mail FSA a few years ago because I couldn't find it but they got straight back to me with the right one.

    If in doubt, get one that's a bit longer. It won't do much harm.

  12. #12
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    https://i722.photobucket.com/albums/...021_192324.jpg

    here is an image of the crank and how it is hitting the frame.. it is the wrong crank. The shop I bought it from I paid 100 bux for the ride is telling me I can return it and trade for a Jamis cross country 2.0 Do you think That would be a good idea or is this worth repairing?

    https://i722.photobucket.com/albums/...igun08/gta.jpg

  13. #13
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    I don't know, I'd want whichever bike is in the best condition! What you could do is moan about them selling you a duff bike and try to get a good deal on the other Jamis. On the other hand, I don't know how confident I would be riding any bike from the shop if they can send out a bike with such a glaring fault on it.

    The shop should be fixing this. It's their fault and even if you give it back to them they'll need to fix it anyway.

  14. #14
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    Yea.. I have made a few deals with shop definitely a low budget operation.. But this one was a disaster.. She is allowing me a even swap for a Jamis Cross country 2.0.. if it is not a pile I will be ok with that.. I paid 100 bux for this one and Hope the Jamis is worth it

  15. #15
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    Or you bent the crank?

    sent with a telegraph

  16. #16
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    no its not bent.. it is not the correct bottom bracket.. It is in constant contact with the frame and has made some serious damage to the frame. I have not ridden the bike more than 6 city blocks and the damage is way more than the rides I did just to test..

  17. #17
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    if that shop keeps operating that way, they will not be in business much longer. I'd get my money back and go somewhere else.

  18. #18
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    Quote Originally Posted by NateHawk View Post
    if that shop keeps operating that way, they will not be in business much longer. I'd get my money back and go somewhere else.
    Man has a point. Putting the wrong BB on a bike and not even noticing that the rings are eating the frame is poor.

  19. #19
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    This is why bike shops get a bad wrap. Lots of shoty ones out there

    sent with a telegraph

  20. #20
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    This was a nightmare.. This person does alot for their community by giving free bikes to under privileged youth and alot of bikes at that.. But their grasp on reality was horrid.. She blamed me for damaging the crank and then complained "why did I need the bike to be perfect?".. Then today when I went to get the Jamis the gears were not adjusted at all.. she said "what did you do?" I rode the bike half a block.. There was no way in getting my money back hopefully this Jamis will work out. It looks ok.. Ugh!~

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