Dismanting Campagnolo Ultra Torque cranks

Discussion in 'Bicycle Mechanics and Repairs' started by dennetti, 7 Apr 2018.

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  1. dennetti

    dennetti Regular

    Location:
    Bristol
    Hi. Am I trying to take my ultra torque cranks apart. I understand its clockwise to unscrew, on the drive side. I am using a lot of force and its just not moving. Its a 10mm hex fastener. Any advice please? Thanks
     
  2. OP
    OP
    dennetti

    dennetti Regular

    Location:
    Bristol
    Sorted thanks, it was a conventional thread so it must have been an Italian version, I think.
     
  3. raleighnut

    raleighnut Guru

    Location:
    On 3 Wheels
    The bolt on the 'hirth (serrated) coupling' I take it.
     
  4. OP
    OP
    dennetti

    dennetti Regular

    Location:
    Bristol
    Yep. Off now. I struggled getting bearings off with screw drivers. Should have used a bearing puller
     
    raleighnut likes this.
  5. winjim

    winjim A youth of interminable age

    The cups have different direction threads, and different 'Italian' and 'British' versions but the bolt holding the Hirth joint is just a regular right handed thread.
     
  6. The OP is sorthed but for reference (and info, @winjim) ...

    In UltraTorque systems, the Hirth joint is RH threaded in all versions 2009-present, except Ti-axle Super Record versions - you can tell the difference easily, if the circular logo around the central hole in the crank is white - the bolt is normal, RH thread, if it's red, it's LH thread.

    Campag made the bolts in Ti different because the thread form used in Ti is different and if they'd left it RH, if users had tried to force a Ti bolt into a steel crank, or a steel bolt into a Ti crank, because of the difference in the thread forms, it will have seized and they'd not have been able to get it tightened, or for that matter, be able to get it out, either ... the basic problem is the way that Ti raises "galls" on other metals when they are (typically) threaded together, and even in Ti / Ti interfaces, a different shaping of the thread is sometimes used to reduce the problem. The small threads on things like derailleur pinch bolts don't cause huge problems but in high-torque, sizeable threads like the Hirth joint, galling can and does produce a problem.

    The BB cup thread difference are - BSC, RH thread on non gear side, LH thread on gear side, Italian, both sides RH threaded.
    BSC is 1.37" x 24 TPI , Italian in a metric form thread, 36 x 1 mm.

    BSC is LH threaded on the drive side to combat thread precession - the tendency of threaded parts that directly interface with a ballbearing system to counter-rotate relative to the direction that the bearing normally rotates in. This is also the reason that LH pedals carry a LH thread. Blame it on the Wright brothers - before they made aeroplanes, they made bicycles and the convention actually stems from them ...
     
  7. OP
    OP
    dennetti

    dennetti Regular

    Location:
    Bristol
    Thanks for this excellent reference info. Much appreciated. Once I cleaned up the bolt for the Hirth joint, I saw there was a right-hand arrow on it with the torque value for tightening. Campagnolo specify 42Nm for my model. Cheers, Mark
     
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