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Truative crank issues.

ambo999fireambo999fire Posts: 20
edited October 2014 in MTB workshop & tech
Hi all,

I usually like to at least introduce myself on forums before piping in with a question but couldn't find anywhere to do so - please point me in the right direction if I am missing something!

I have a Giant Yukkon FX2 2009 - it's an old bike but I still love it! I have been experiencing some issues with the crank and am hoping for a bit of advise.

First problem is that the left crank keeps falling off - it is a Truative crank set with square taper BB. I have read around a bit and see it is a common fault, I have tried torquing it up to 45nm as advised on lots of sites, I have even tried using locktite, this seems to work for a couple of hundred miles but it always seems to fall off at some point! The BB seems to be OK - no visible damage to it.

The other problem I have is that I have problems shifting into the top cog - I have adjusted and adjusted the front mech but still it won't go into the top cog unless I am descending and there is no load, If I am climbing when I try to shift to the top cog it usually throws the chain off. I noticed on my turbo trainer the other day that when I select the top cog, The chain seems to oscilate - it starts to move to the top cog, then slips back down etc. This happens at the same crank angle every time which makes me think that the top cog is bent - does this sound plausible?

I am planning on replacing the front crank set but want to make sure I make the right choices! Since I have SRAM gear on the front do I need to stick to a Truative crank or can I consider any other options? Should I stick with the square taper BB system, or is there something else I should be considering? If I stick with square taper should I replace the BB anyway? I am not a hardcore rider any more (it hurts too much when you get older!) but do enjoy a nice fast downhill run from time to time and I like to get muddy whenever possible! I also enjoy the satisfaction of a punishing climb - my reward being what goes up must come down! I am not made of money - I am a student again, except this time around I have a mortgage to pay and little mouths to feed - but I don't want to throw away money buying something that won't last 5 minutes (hoping to spend less than £100).

So what should I buy?

Posts

  • cooldadcooldad Posts: 32,904
    If the chainring is moving, could be the BB is stuffed. Or it's just not adjusted properly.

    Read Parktools - link below.

    Once a square taper crank has come loose and ridden, it's basically dead.
    You can put any square taper crankset on, but BB axle length is crankset specific, so unless the one you buy needs the same length, you'll need to match it with a BB anyway.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • cooldadcooldad Posts: 32,904
    Or have the BB shell faced (about tenner at your LBS) and stick one of these on. Comes with a BB and makes life simpler in future.

    http://www.chainreactioncycles.com/shim ... -prod40496
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • Thanks for the advise cooldad. I guess I will replace the lot then, BB and crank set - I also want to upgrade my top cog from 42t to 44t. So should I stick with square taper or should I consider octalink or similar? Also will any crankset work with my sram front mech or do I need to match them?
  • Whoops, I guess you just answered those questions in your second post! Thanks again for the advise.
  • cooldadcooldad Posts: 32,904
    Front mech should be fine - if you put a bigger ring on you will need to move it up slightly so check there is a bit of free space. Just needs a mm or two.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
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