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Changing crank and bottom bracket

Graham of MadridGraham of Madrid Posts: 9
edited January 2019 in MTB workshop & tech
Hi there !

I’m a new member and need some help. I’m going to change the crankset and bottom bracket but it’s a job I’ve never done before. There's a lot of information around for newer bikes with more expensive components but my bike is relatively different. Overall, the transmission on this bike has covered a lot of miles and has been replaced piecemeal, it’s had a few cassettes, cable inners/outers, chains and a bottom bracket but it all needs replacing now. I’ve had this done in the past at the bike shop but this time round I’m doing it.

I’ve got a 2012 (3 * 8 speed) MTB which came from the factory with a Suntour SR XCT crankset (3 piece crank with square tapered spindle, cranks are 175mm long., the tooth difference is 42T 32T 22T). Problem is that the chain rings are worn and need replacing and I don’t know what to replace it with. The crankset seems to be a budget item where the individual rings are riveted on so a complete replacement is required.

I would like to find a replacement item which won’t break the bank and will be a plug and play fit not requiring any alteration to the Shimano Alivio front derailleur. I don’t know which brand I should choose, Shimano, SRAM or Suntour - hopefully someone can provide me a link to the sort of items I should be looking at ?

I need a link to the tool which removes the bottom bracket. I’ve seen a variety of splined tools but not sure exactly what I need. e.g I saw an ISIS tool but I'm not sure if it's for the bottom bracket or the crank.

Any help appreciated.


  • The RookieThe Rookie Posts: 27,748
    Standard crank puller, though its worth getting one for ISIS/Powerspine/Octalink with the extra button on the tip in case you change use one of those in the future.

    You can fit a wide range of BB and cranks, this would be a decent option at a good price ... :rk:9:pf:0
    Yes 9 speed cranks will work with 8 speed and no you won't need to change front mech!
  • Hi there, thanks for your reply.

    The crankset you linked me to has 44 teeth, mine has 42. Does that mean I have to move my front derailleur up on the seat tube ?

    It's length is also 170 instead of 175 that I have. Is this much of a difference ?

    I'm curious why you chose that crank out of all the ones available. I'm assuming I can use Shimano, Suntour or SRAM.

    Thanks for the info about the crank puller, great idea to get one. I do need a link to the tool which removes the BB as I'm not sure what tool I need.

    Thanks again !
  • JBAJBA Posts: 2,721
    If you are happy with the current chain set you could just replace like for like. An XCT chain set is less than £30.
    Example HERE.

    Bear in mind that if your chain rings are worn then your chain and cassette will probably also need replacing.
    “Life has been unfaithful
    And it all promised so so much”

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  • The RookieThe Rookie Posts: 27,748
    You could just replace the cranks as noted, but I'd wonder how long the BB had left.

    Yes you may need to lift the front derailleur up the seat tube by maybe 4mm, or maybe it will be fine.

    Puller ... r-EV348508
  • larkimlarkim Posts: 2,301
    The only real choice on a like for like replacment is whether to go with a crank which has fully removable chainrings I suppose.

    Higher spec will come with more removeability.

    Be prepared for a quite physical task in pulling the cranks if my previous experience of removing Suntour cranks from square BB.

    I can't quite tell from your original post whether you've already pulled the cranks or not, so just need the BB tool, or if you need to pull the crank first and are also thinking about the BB. BB is the easier job to do in my experience and always results in a nice smooth pedalling experience!
    2015 Canyon Nerve AL 6.0 (son #1's)
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  • billycoolbillycool Posts: 833
    I think the OP hasn't done anything yet but wants to replace BB and cranks.

    As suggested, like for like is possibly the cheapest option. Replacing the BB at the same time is deffo a good idea.

    It's been said already but if your chainrings are that worn, then a new chain and rear cassette would be sensible.

    If you want to spend more and have replaceable chainrings and more crank options, then you could go for a posher BB and go for something like a Hollowtech: ... m-bracket/

    You could then fit a crankset to work with that but it adds more cost.

    You can spend the bare minimum or get some posher bits that may or may not have any impact on your riding enjoyment.
    "Ride, crash, replace"
  • Hi Guys, thanks for your help.

    I'm definitely changing the BB as the crank has movement due to wear and the chain and crankset will be changed at the same time.

    Where I am in Spain I would have to pay 10 quid for shipping the S R Suntour XCT Black 22-32-42 Alloy 175 arm Chainset. It is not available locally !!

    I'm not sure if its worth looking at more expensive options if I can't quantify the extra costs or rider benefits. I'm not spending money for the sake of it but I'm not adverse to investing in quantifiable improvements.

    Going back to cranksets can I use any manufacturer ?

    Thanks again !
  • I will change the cassette too, I'll have to find research how to identify exactly what I need and how to fit it and I've got problems with the Shimano shifters too so it's the whole transmission, probably cable outers too.
  • Vino'sGhostVino'sGhost Posts: 4,129
    might as well buy a whole groupset on a deal. it might work out cheaper.
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