Cobb 155mm crank.. should there be play when installed?

Discussion in 'Road Series (S1.x, S2.x, S30, S40)' started by cpml123, Jan 10, 2018.

  1. cpml123

    cpml123 Member

    Hi all,
    I just installed Cobb 155 50/34 crankset on my S40. I had Sram Rival crank and BB. Since it's GXP compatible, Robert said I should be able to take off the Rival crank and install the new crank easily. It did install fine. However, I found the new crank has a little play, my guess about 1 or 2mm. Is that normal? I did torque it to 35 ft lb as instructed. Is this manufacturing issue? Help!
     
  2. ratz

    ratz Wielder of the Rubber Mallet

    Sounds like you need to add a wave-washer to get the proper torque.

    24mm
    http://www.enduroforkseals.com/id435.html

    These are also helpful
    24mm x 1mm
    http://www.enduroforkseals.com/id433.html
     
  3. ReklinedRider

    ReklinedRider Zen MBB Master

    Just from experience with Cobb cranks: remove the crankset from your bottom bracket and shell. Put the crank arm on the spindle as if you were installing it on your bike. Torque to spec, then torque it some more. Ditch the torque wrench for the moment and tighten it down **unreasonably** tight (remember this is with it off your bike). Disassemble and reinstall on your bike. Should tighten down nicely with no play. I recently installed two Cobb cranksets and I had the same amount of play you are describing. Tightening the arm on the spindles really tight, off the bike, worked well. I don't know why this seems to be a problem with these now; I have installed Cobb's in the past with nary a hitch.

    Before I did that extra-tight maneuver I had called Cobb; the person answering the phone didn't have an answer and said "hang on". The next voice on the line said, "Hi, this is John Cobb". He was perplexed and sent me a new crank arm the next day. Same problem with it, though. I admit I was frustrated when I took it apart and tightened it down <excessively>. But it worked. {The point of this paragraph is that Cobb offers great customer service. Maybe give them a call and see what they say.}

    (I'm assuming you didn't use any spacers on your bottom bracket. Using the MTB spacers creates a problem too. More experience:oops:)
     
    super slim likes this.
  4. cpml123

    cpml123 Member

    No I didn't add any additional spacer. I just left the little gasket as is from the Sram BB.
    I did find a wave-washer in the box with Cobb BB that I did not use.

    Kline - did you install a wave-washer with your crank or you just pre-tightened and re-installed the crank without the wave-washer?
    Bob - if I were to use the wave washer - do I use on the drive side or non-drive side?

    Thank you!
     
  5. cpml123

    cpml123 Member

    OK. I clicked on the link that Bob has for wave-washer. It says it can be used for threaded GXP drive side. So I tried to get the wave washer that's included in the Cobb BB box onto the spindle, and the tolerance was so tight that I couldn't get the washer onto the spindle. So I gave up and tried Kline's method of pre-torquing the crank arm and reinstalling it. Now the crank arm went on with no left-right play (along the spindle axis) and tightened onto the BB at 35 ft lb torque. However, when I tried to rock the crank rotationally (imagine if you look at the bike head-on, hold crank arms with both hands, and try to twist the whole bike clockwise/counter-clock wise using the crank arms), there was a slight play. It seemed to come from the BB itself. I don't know it's normal but I am thinking it's probably good enough for now, I hope.
     
    super slim likes this.
  6. ReklinedRider

    ReklinedRider Zen MBB Master

    i didn't use a wave washer.

    i see what you mean about the rotational play. mine doesn't do that.

    not familiar with the little gasket from the sram bb. i used the bb that came with the cobb crankset.
     
  7. cpml123

    cpml123 Member

    Kline.. Thank you for the pointer that yours doesn't have rotational play. I went back and loosened the crank arm by a few rotations. I then tightened it again to 35 ft lb, and now the crankset and bb are completely tight.

    It's kind of odd that the crank has to be tightened, loosen, and tightened again vs being tight and no play the first time.
     
  8. ratz

    ratz Wielder of the Rubber Mallet

    The wave washer is for bearing life it preloads the torque so the bearings stay in the races; goes on the crank side. You don't need it but your BB will wear our sooner without it
     
  9. cpml123

    cpml123 Member

    Hi Ratz... does the wave washer go on the drive sprocket side or the non drive side?
     
  10. ratz

    ratz Wielder of the Rubber Mallet

    Chain Ring side, the non drive side on a GXP is self aligning self torquing. If should be noted if you are using a $30 BB don't bother. If you are using a $125-200 BB don't skip it.
     
    ReklinedRider likes this.
  11. cpml123

    cpml123 Member

    Noted. When my current cheap BB gets replaced in the future with a better BB, I will put that in.

    It's just that washer was so impossible to get on the spindle due to tight tolerance. Any tips on getting the washer onto the spindle? Or just get a bigger washer?
     
  12. ratz

    ratz Wielder of the Rubber Mallet

    make sure it's a 24mm one and grease.
     
  13. ReklinedRider

    ReklinedRider Zen MBB Master

    I agree. SRAM cranks....no such problem.
     
  14. cliff oliver

    cliff oliver New Member

    I have same issues. Tighten (over 35lbs) loosen, re-tighten. I have enduro BB use the washer on drive side they provide. The SRAM cranks no problem, but I sure like this shortened COBB crank. What a difference 15mm makes.
     
    super slim likes this.
  15. cpml123

    cpml123 Member

    Oh good. I guess it's a "feature" we pay for. I won't bother to call to complain then.

    I will save the washer for the future BB.
     

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