crankset compatability issues

crispy1980
crispy1980 Posts: 310
edited June 2012 in MTB workshop & tech
hi all, i have just replaced the cassete, crankset and chain on my gt aggressor xc3. however the crankset doesnt seem to be compatable. the front mech does not have enough travel to select the large chain ring. there are some differences to the design of the crankset too, the old one ( suntour ) has a dished small chain ring whereas the new one ( shimano alivio ) does not. the effect of this is that the new cranset sits slightly further out which is what is causing the issues. have i bought the incorrect crankset?

its this one

http://www.chainreactioncycles.com/Mode ... elID=46025

Comments

  • nicklouse
    nicklouse Posts: 50,675
    you will need to get new BB with the correct axle length.

    what is the current axle length?

    you need a 113mm axle.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • crispy1980
    crispy1980 Posts: 310
    ive no idea tbh, i naively assumed that any square taper would fit.there doesnt seem to much nroom to get any closer in, or would the correct bb be narrower as well?
  • nicklouse
    nicklouse Posts: 50,675
    cranksets need the correct BB and axle length. there are axle lengths from 108mm to 128mm and if you dont have the correct one things dont work.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • crispy1980
    crispy1980 Posts: 310
    does it follow that i may have an odd size then? as crc dont seem to list any measurements for specific cranksets so im assuming that a large proportion of bikes use certain size?
  • nicklouse
    nicklouse Posts: 50,675
    crispy1980 wrote:
    does it follow that i may have an odd size then? as crc dont seem to list any measurements for specific cranksets so im assuming that a large proportion of bikes use certain size?
    why assume that. you are have not even replaced with the same make let alone the same model.

    CRC dont list it as there are so many options variations.

    here is just a small example
    http://bike.shimano.com/publish/content ... 0Chart.pdf

    and if you have a frame that needs a differnt chain line then you would also need a different Axel length.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • crispy1980
    crispy1980 Posts: 310
    soory to sound dumb, but how do i work out what i need then? if i change the bb for a 113mm spline length, would this then cause the chain to run crooked as the front is going to be further out? do i need to maintain the bb length and find a crank set to suit? cheers, chris
  • nicklouse
    nicklouse Posts: 50,675
    i have told you want you need see my first post.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • crispy1980
    crispy1980 Posts: 310
    i understanmd that ineed to match the axle length to the crankset but what about this chain line business? you said some frames may require specific axel lenght?
  • nicklouse
    nicklouse Posts: 50,675
    yes. and the cranks you have bought are for one chain line only which needs the axle length stated.

    which is/was the standard for most bikes. and which the cranks you had fitted it is very unlikely that you would have anyother chain line.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • crispy1980
    crispy1980 Posts: 310
    ok thanks very much, might asa well have a new bb as well then and get nearly every thing replaced, hopefully the end of my trouble some gears! thanks again, chris

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