Installing New Crank On Square Taper BB

kurth
kurth Posts: 57
edited February 2011 in MTB workshop & tech
Hi all

I have removed my old crankset and I'm trying to install a new crankset onto my square taper BB.

The crank arms seem too tight though, how am I supposed to get them on correctly where they should be (they won't slide all the way on)?

Please help

Thanks
«1

Comments

  • *AJ*
    *AJ* Posts: 1,080
    The crank bolt pulls it on further because it's tapered. It's supposed to be tight.
  • kurth
    kurth Posts: 57
    So if I just keep tightening it until its on fully it should be ok?
  • nicklouse
    nicklouse Posts: 50,675
    unttill it is at the correct torque setting.

    also how do you know where it "should" be?

    and the cranks do have the same Taper standard?

    what is the BB and what are the cranks?
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • stu8975
    stu8975 Posts: 1,334
    Use a torque wrench, not tight enough and it may come loose and you'll be buying another one. Too tight and the square taper hole will be enlarged...and you'll be buying another one.
    ANTHEM X
    Youth
  • craker
    craker Posts: 1,739
    Are you sure you're old bottom bracket axle is the right length for your new crankset? Different cranksets need appropriately sized axles.

    Sheldon Brown has a fairly comprehensive database of bottom bracket lengths though I've no idea how up to date it is.
  • TuckerUK
    TuckerUK Posts: 369
    edited February 2011
    Make sure to grease the tapers and the bolts first to prevent spalling.

    If you don't own a torque wrench, I've never had any problems just using grease and doing them up as tight as I reasonably can using a standard socket handle. I own three torque wrenches, never used them for this job though.

    Even though common wisdom says you can do them up too tight, I've never found that to be the case.

    What the experts say: http://www.sheldonbrown.com/brandt/inst ... ranks.html
    "Coming through..."
  • kurth
    kurth Posts: 57
    It's the following:-

    Shimano BB-UN 26 / 68-113mm

    Shimano Deore Hollowtech Crankset (M510)
    http://www.sprockets.uk.com/shimano-m51 ... jir12hdk02

    I'm not sure tightening it is doing it any good, it sounds like somethings going to break?!
  • TuckerUK
    TuckerUK Posts: 369
    Read the link I added to the bottom of my post above yours.

    If in doubt, and you haven't yet got that feel for fastener tightening that only comes with years of practice (and years of stripping threads/rounding heads) then perhaps you know someone who has, or your local bike shop might help?
    "Coming through..."
  • nicklouse
    nicklouse Posts: 50,675
    I am sorry but GREASE is a BIG NO on square taper cranks.

    UNLESS the manual says yes. EG Race face on some of their cranks.



    could you please just check the part number stamped on the back of the arm.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • kurth
    kurth Posts: 57
    This is it:-

    IMAG0202.jpg

    This is how it fits (or doesn't fit)

    IMAG0204.jpg

    IMAG0203.jpg

    According to Sheldon Browns 'thing' my chainline should be 47.5/50mm, mine's currently 55.5/60mm and I've tightened it as much as I physically can? :oops:
  • Andy B
    Andy B Posts: 8,115
    That looks normal, the arms hardly ever go all the way to the end of the square tapers
    2385861000_d125abe796_m.jpg
  • TuckerUK
    TuckerUK Posts: 369
    nicklouse wrote:
    I am sorry but GREASE is a BIG NO on square taper cranks.

    Myself (mechanical engineer since 1981), Sheldon Brown, and Jobst Brandt all disagree with you. Read the link, and/or provide your reasoning.
    "Coming through..."
  • Andy B
    Andy B Posts: 8,115
    Most manufacturers (Specialites TA and White Industries being notable exceptions) recommend that square-taper cranks be fitted to the bottom bracket "dry", with no grease or other lubricant

    http://en.wikipedia.org/wiki/Bottom_bracket

    And nowhere in any shimano tech docs is there any reference to using grease on the square tapers.
    2385861000_d125abe796_m.jpg
  • kurth
    kurth Posts: 57
    Does it look wrong them TuckerUK and why is my chainline out? Please help
  • *AJ*
    *AJ* Posts: 1,080
    Bottom bracket is too long.

    They are on the tapers fine, but stick out more than your old ones as the BB is too long for that model by the looks of it. Looks like they would use a 110 or 108 BB
  • TuckerUK
    TuckerUK Posts: 369
    Andy B wrote:
    Most manufacturers (Specialites TA and White Industries being notable exceptions) recommend that square-taper cranks be fitted to the bottom bracket "dry", with no grease or other lubricant

    http://en.wikipedia.org/wiki/Bottom_bracket

    And nowhere in any shimano tech docs is there any reference to using grease on the square tapers.

    Please, read the link, it explains all that.

    Does anyone have a good reason to back up their opinion? I do. I've been using square taper since it wasn't even called that, it was called cotterless. I've never had one of my square taper cranks come loose. I've seen plenty fitted dry come loose though, even those factory fitted.

    Now, I'm not smart enough to explain exactly why that should be so, but luckily I know a man who his, and I've linked to his article (hosted by the late cycle guru and expert mechanic Sheldon Brown) which explains my findings perfectly.
    "Coming through..."
  • TuckerUK
    TuckerUK Posts: 369
    edited February 2011
    kurth wrote:
    Does it look wrong them TuckerUK and why is my chainline out? Please help

    Hmmm, BB axle length matches what I believe to be correct for that crankset. How are you measuring chain line? Did you check the BB axle length prior to install? Might be labelled wrong?

    EDIT:

    It doesn't look obviously wrong to me, I'm going by your chain line measurement.

    I don't have a square taper bike here to compare, but tomorrow I will be at my sons, and he has one. I'll take some photos for you, post them tomorrow evening.
    "Coming through..."
  • *AJ*
    *AJ* Posts: 1,080
    Do you actually have any problems with it apart from it not 'looking' right?

    As for the grease thing I've always used a bit of grease on square tapers, and never had an issue with them. It keeps them quiet too! Dry fit will often develop a creak.
  • kurth
    kurth Posts: 57
    TuckerUK wrote:
    kurth wrote:
    Does it look wrong them TuckerUK and why is my chainline out? Please help

    Hmmm, BB axle length matches what I believe to be correct for that crankset. How are you measuring chain line? Did you check the BB axle length prior to install? Might be labelled wrong?

    EDIT:

    It doesn't look obviously wrong to me, I'm going by your chain line measurement.

    I don't have a square taper bike here to compare, but tomorrow I will be at my sons, and he has one. I'll take some photos for you, post them tomorrow evening.

    Thanks mate :D
  • TuckerUK
    TuckerUK Posts: 369
    Just out of interest, what tool are you using to tighten it up?
    "Coming through..."
  • TuckerUK
    TuckerUK Posts: 369
    FWIW

    "Always clean and lightly grease the axle tapers or splines before fitting cranks. This contradicts advice which is often given, but anyone suggesting that grease shouldn't be used either doesn't have any mechanical understanding or has a vested interest in shortening the life of your cranks."

    on http://www.highpath.net/ Cycle information BB
    "Coming through..."
  • Andy B
    Andy B Posts: 8,115
    TuckerUK I have read the link & I disagree with greasing square taper bottom brackets, unless the installation manual says so I do not grease them & have had no problems on the hundreds I have fitted.

    but what would I know, I've only been repairing cycles for 20 years and work as a full time professional cycle mechanic and run a mobile cycle repairs business.
    2385861000_d125abe796_m.jpg
  • TuckerUK
    TuckerUK Posts: 369
    edited February 2011
    Andy B wrote:
    TuckerUK I have read the link & I disagree with greasing square taper bottom brackets, unless the installation manual says so I do not grease them & have had no problems on the hundreds I have fitted.

    but what would I know, I've only been repairing cycles for 20 years and work as a full time professional cycle mechanic and run a mobile cycle repairs business.

    We (that's me as an engineer, and three professional sources) will have to just agree to disagree with you then, make no odds to me. Vive la difference!
    "Coming through..."
  • TuckerUK
    TuckerUK Posts: 369
    edited February 2011
    Now, my son has just taken a pic and sent me.

    His non drive side crank is almost touching the BB. So yes, yours is not right. So, either both items aren't the same square taper standard (I'm not sure Shimano even use the other standard), your BB axle is too long, or you haven't tightened anywhere near enough (and without grease it is so much harder/impossible to seat them correctly).

    You can double check your BB axle length, which just leaves tightened the buggers up. I use an allen key socket, and an old broken torque wrench will extra long handle. As per the article, I do them up as tight as I dare, I've never cracked one. But, that's easy for me to say, it's your money/bike, if in doubt, get some help.

    Don't ride with the cranks not done up correctly though, once they are allowed to wobble they are knackered.
    "Coming through..."
  • TuckerUK
    TuckerUK Posts: 369
    large.jpg
    "Coming through..."
  • kurth
    kurth Posts: 57
    Thanks for all the info Tucker.....I have just compared the old and new crank arms and the thread inside the new crank arm is half the size of my old cranks thread, so I'm guessing that's why the fit isn't as snug as the old one and it's not as close to the bb......
    ......I've tightened it as much as possible using a socket wrench. It definately won't come off (I used a bit of grease too as you said)

    I'll give it a try and see what happens.....

    ....wish me luck,lol
  • Andy B
    Andy B Posts: 8,115
    How far along the taper the crank arm goes depends on the crank arm itself, tolerances and differences between manufacturers all play a part

    Just because your son's goes that far along the taper does not mean that the cranks in question on this thread go on as far as your son's

    Nor does it mean that the crank arm in question should be as close to the BB shell as your son's are.

    I'm washing my hands of this thread now, as obviously I know nothing, nor do any of the other contributors to this thread who haven't got engineering degrees, built several race cars, hundreds of cycles, work for major car manufacturers in their engineering departments or worked as professional cycle mechanic for years...
    2385861000_d125abe796_m.jpg
  • nicklouse
    nicklouse Posts: 50,675
    so what is the chain line?

    still having fun finding the crank on the data base.

    but it looks fine to me.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • kurth
    kurth Posts: 57
    There's no info on this crank anywhere......it does appear on that sheldon thing but doesn't really say much

    The chainline is 55mm :?

    The crank definatley won't go on no more.....that's as far as I can get it! :x
  • *AJ*
    *AJ* Posts: 1,080
    I'l ask again.... Are you having any problems with it apart from thinking it doesn't look right?

    Can you get the chain on all 3 chainrings?

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