Dura Ace bottom bracket

greasedscotsman
greasedscotsman Posts: 6,962
edited October 2010 in Workshop
Do I need to change the bottom bracket if swapping a Dura Ace 7900 standard chainset for a 7950 compact chainset?

Comments

  • domhopson
    domhopson Posts: 259
    No you shouldn't do for a standard to compact, but may do if you changed to a triple
  • dmch2
    dmch2 Posts: 731
    Why might you need to change it if it were a triple?
    2010 Trek 1.5 Road - swissstop green, conti GP4000S
    2004 Marin Muirwoods Hybrid
  • JohnnyAllez
    JohnnyAllez Posts: 785
    BB`s are the same, for info..... triple has a big plastic spacer fitted behind the drive-side crank, that`s all.

    Changing from a standard-double to a compact-double just means dropping the front mech down a bit.
    Jens says "Shut up legs !! "

    Specialized S-Works SaxoBank SL4 Tarmac Di2
  • dmch2
    dmch2 Posts: 731
    Aha! That explains why my hybrid's chain rubs in 1st and 2nd gear on the granny ring even with the front mech's stop wound fully in. I need to fit the spacer!

    It's got a DA BB as it was massivley reduced (old model perhaps?) and the other (cheaper) hollowtech II shimano BB was out of stock at wiggle at the time.
    2010 Trek 1.5 Road - swissstop green, conti GP4000S
    2004 Marin Muirwoods Hybrid
  • dmch2
    dmch2 Posts: 731
    I've got 3 spacers that are all the same, about 1.5mm thick. How many of them will i need?

    (@OP sorry for the topic hijack!)
    2010 Trek 1.5 Road - swissstop green, conti GP4000S
    2004 Marin Muirwoods Hybrid
  • greasedscotsman
    greasedscotsman Posts: 6,962
    dmch2 wrote:
    (@OP sorry for the topic hijack!)

    No worries, you can't beat a bit of topic hijack. But I am a bit confused now, I was asking about 7900 Dura Ace and now we're onto triples. As far as I knew, there isn't such a thing as a 7900 triple?
  • dmch2
    dmch2 Posts: 731
    I think that...

    If you got the same type of cranks expecting the same type of BB then you don't need to change anything.

    So you're fine :)

    If you go from 2 to 3 rings but same everything else then the BB still doesn't need changing but you need to add a spacer.

    When I changed my BB and chainset from square taper to hollowtech II (both triples) i didn't put a spacer in. So i need to add one (or two? Or all three?)

    I think..!
    2010 Trek 1.5 Road - swissstop green, conti GP4000S
    2004 Marin Muirwoods Hybrid
  • JohnnyAllez
    JohnnyAllez Posts: 785
    Sorry for the going off-topic onto triples Greasedscotsman :wink: What you`re wanting to do won`t involve any BB swapping.

    Neither will fitting a triple, you just need the thick spacer behind the drive-side crank,

    for DMCH2................

    http://bike.shimano.com/media/techdocs/ ... 676705.pdf

    Item 11 on the picture, note where it goes :wink:
    Jens says "Shut up legs !! "

    Specialized S-Works SaxoBank SL4 Tarmac Di2

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