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Help figuring out the correct replacement BB and crankset

danstar10danstar10 Posts: 13
edited February 2014 in MTB workshop & tech
So after a hell of an ordeal getting a set of old cranks off and bottom bracket out, I now need to figure out which replacement parts to order so I would really appreciate any advice!

Here are the details:
Old BB was 68mm * 117mm
Old crankset was Shimano Altus with 38 31 22 rings or something similar
The front derailleur is BB mounted

So far I have found two cranksets that seem suitable:
http://www.chainreactioncycles.com/shim ... -prod46021
http://www.woollyhatshop.com/Cranksets/ ... _3149.html

and here are the shimano techdocs for both of those:
M442
http://techdocs.shimano.com/media/techd ... 657937.pdf
FC131
http://techdocs.shimano.com/media/techd ... 758324.pdf

So from what I can derive it looks like the fc131 needs a 122.5mm spindle, but I cant figure what the M442 needs. There is also the (-E) and (-K) prefixes that I know relate to front derailleur type but I don't get how to use that info - can anyone shine some light on that? As I said my derailleur is mounted on the bottom bracket. If it says (-e) after a certain bottom bracket, does that mean it is what I should use, and (-k) I should not use?

So can anybody figure out which crankset / BB spindle length combo I should go for?

As for the BB I guess I will go for UN-26 or UN-55

Thanks in advance

Posts

  • nicklousenicklouse Posts: 50,675 Lives Here
    Sure we can but what are we doing?

    Are you keeping the existing BB?

    You don't say.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • nope the old BB is dead too so I also need to replace that
  • jimothy78jimothy78 Posts: 1,407
    In that case, the world is your shellfish of choice. You can effectively choose a crankset, then pick up the right bb to go with it. Of the two you linked to, the M442 is a much better option, as it has replacable chainrings. It appears that a spindle length of 110-113mm is right for that one, and the UN55 also sold by ChainReaction will be a perfect fit, I think.

    However, it's worth bearing in mind that you could also get a hollowtech II chainset and BB (although you'd probably need to get the BB shell faced before fitting.
  • Thanks, I decided against the hollowtech / other interfaces as it is a cheap bike I am fixing up for as little as possible.

    So does the fact that the front derailleur is bottom bracket mounted not affect my choice? for its purposes the FC131 crankset would be just fine, it is just a bike to runaround the city, so whichever combo is cheapest / more suited to my set up really.
  • jimothy78jimothy78 Posts: 1,407
    danstar10 wrote:
    Thanks, I decided against the hollowtech / other interfaces as it is a cheap bike I am fixing up for as little as possible.

    Sure, no worries, I actually think there's a lot to said for ST, anyway.
    So does the fact that the front derailleur is bottom bracket mounted not affect my choice?
    Ideally, you should get a BB designed to work specifically with an e-type fitting, as they have a little unthreaded section and an extra wide lip to hold the e-type mech in place. In fact, I think I have one knocking around in the garage - I'll have a look for you.
    for its purposes the FC131 crankset would be just fine, it is just a bike to runaround the city, so whichever combo is cheapest / more suited to my set up really.
    Sure, but it would only be cheapest in the short run, as you'd be throwing the whole lot away once one of the chainrings was badly worn, instead of just buying a new chainring.
  • Ok cool so with that in mind, looking at the techdocs there is not a BB listed with the FC131 that has a (-e), but the M442 lists the BB-UN26 (-E)

    Then under that BB on the same sheet there are two options:
    MM110 (E) - 47.5 mm
    LL113 (E) - 50mm

    I'm not sure what the differences are between these. I think the measurements are chainline - is that the only difference? Is there a way for me to know which chainline is correct for my setup?

    Thanks, yeah let me know what you have lying around in your garage but guess it would be pretty lucky if it were one with a suitable spindle length!

    This really is a runaround bike so longevity of the crankset is not really a concern as I don't foresee having it too long and it does not see many miles.
  • i really wouldn't worry too much, fit one that is longer than your current and there shouldn't be any issues. You may have to adjust the front mech cable tension but i wouldn't sweat it too much.

    Alternatively fit a cheap single speed crankset to save weight and cost.
  • jimothy78jimothy78 Posts: 1,407
    danstar10 wrote:
    Then under that BB on the same sheet there are two options:
    MM110 (E) - 47.5 mm
    LL113 (E) - 50mm

    I'm not sure what the differences are between these. I think the measurements are chainline - is that the only difference? Is there a way for me to know which chainline is correct for my setup.

    Yes, the only difference between the two spindle lengths would be the resulting chainline. I'm not sure, but i believe 47.5mm used to be standard, but this got pushed a bit to make way for larger diameter seattubes, and now most systems work with 50mm (again, not 100% sure, but think all the hollowtech cranks are now designed to give a 50mm chainline).

    I think the in the real world, you'd be unlikely to notice any negative effects of using one versus the other unless you're really censored , and as you're planning a rough bike, I don't think it would be anything to lose any sleep over.

    As it happens, I have got an e-type BB in the garage. It's a Shimano LP28 68x110-E , english thread. Been fitted to a bike but never used, as I realised then that I needed the standard one not the e-type, and it's been sat in the garage ever since. If that's any use to you, you can have it for a fiver including postage.
  • Thanks jimothy78, that's very kind of you, but if I can get this one
    http://www.chainreactioncycles.com/shimano-un26-square-taper-bottom-bracket/rp-prod34652
    for that price it makes sense to do that. How can I tell if this one is a (-e) BB designed for a BB mounted front derailleur?
  • jimothy78jimothy78 Posts: 1,407
    danstar10 wrote:
    Thanks jimothy78, that's very kind of you, but if I can get this one
    http://www.chainreactioncycles.com/shimano-un26-square-taper-bottom-bracket/rp-prod34652
    for that price it makes sense to do that. How can I tell if this one is a (-e) BB designed for a BB mounted front derailleur?

    if it was, the code would read "UN26-E", otherwise it's standard, I think. Alternatively, CRC might list it as one of the options, like they do here (obviously this isn't a suggestion, just an example):
    http://www.chainreactioncycles.com/shim ... rp-prod908
  • Ah I see. I have contacted CRC to ask them, I assume they will not have it by the looks of things so I may just take you up on your offer.

    Last few questions hopefully!:
    As my last BB was 117mm, do you think your 110mm will be ok on my frame clearance wise?
    My bike is 8 speed and the M422 crankset is listed as 9 speed, I assume that will not be an issue?
    My old biggest ring was 38, where as the M422 is 44, again I assume as long as my chain has the length this will be a non issue?

    Thanks!
  • jimothy78jimothy78 Posts: 1,407
    danstar10 wrote:
    As my last BB was 117mm, do you think your 110mm will be ok on my frame clearance wise?
    should be - my understanding is that spindle length is determined entirely by the profile of the chainset, nothing to do with the frame itself.
    My bike is 8 speed and the M422 crankset is listed as 9 speed, I assume that will not be an issue?
    Correct - the chainring teeth will be ever-so-slightly thinner than absolutely necessary, but will still happily run an 8-speed chain.
    My old biggest ring was 38, where as the M422 is 44, again I assume as long as my chain has the length this will be a non issue?
    The only potential issues I can think of are that:
    1) if the original chain was shortened to the absolute limits of the previous set-up it may be a couple of links too short. However, you can pick up a new 8-speed chain (including a powerlink) at tesco for £4, so if I were you I'd be treating myself anyway (always wise to start a new chain when you replace a chainset or cassette, as an old one may cause premature wear), then you can shorten it to the correct length for your new setup.
    2) The larger chainring might cause clearance issues with your e-type front mech (as you can't raise or lower it). By my calculations, the chainring will be about half an inch larger in radius, so you'd need to currently have at least half an inch spare between the current ring and the cage of the mech (hope that makes sense).
  • raldatraldat Posts: 242
    Jimothy, I can confirm that, the spindle length is determined by the crank not the frame. For example, I had an old non series shimano crank with a 122mm spindle and put an alivio on with a 113 spindle and it was perfect.
  • Ok great, thanks for your patience in explaining everything, makes perfect sense!
    Do you happen to have a link to that particular chain from Tesco? Or did you buy it from a store and not online?
    I will try to reassemble the old chainset / BB / derailleur setup off the bike to see how much space it looks like I'll have for the 44 tooth chainring. I think your calcs are pretty accurate as I did some more research on chainring diameters and it looks like 12.5mm extra in radius which is pretty much exactly half an inch.
    As it stands I'll wait for CRC's response to my query, I guess it will be monday / tuesday, then let you know concerning your kind offer of your old BB :)
  • jimothy78jimothy78 Posts: 1,407
    danstar10 wrote:
    Do you happen to have a link to that particular chain from Tesco? Or did you buy it from a store and not online?
    I just picked one up in store, as it's in their basic range, and as such should be available in all their larger stores, but it's listed here as well (I know it says up to 21gears (7-speed), but 7- and 8-speed chains are identical in all but name).
  • Just got a response from the guys at CRC:

    "The UN26 bottom bracket can be used with E-type front derailleurs. It has a lip on the drive side cup that can hold E-type derailleurs and chainguide's."

    So I am going to go for their BB for now jut to avoid any potential problems from buying from a forum, although I am sure it would be fine!

    Thanks very much for your help jimothy78, much appreciated! I will try to update this thread if / when I have everything up and running.

    Cheers
    Dan
  • jimothy78jimothy78 Posts: 1,407
    No worries, good luck with it.
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