stem slip?

the great cornholio
the great cornholio Posts: 33
edited September 2008 in Workshop
I have a strange and annoying problem with Aheadset adjustment on forks with a carbon steerer. I would great appreciate any advice.

I have an alloy 1 1/8 " stem and a steerer tube bung (not star nut). I have 2 x 10mm alloy spacers below the stem.
Several times I have adjusted the headset to the point where it seems just right (not loose on rocking with front brake applied, but still smooth). I them lock down the stem and ride. At some point, after 50-60 miles, the headset will suddenly become very stiff, requiring me to stop and readjust before continuing to ride.
This seems always to happen on sustained climbs, when I am standing and pulling on the bars. I can only think that the stem is somehow slipping or creeping down the steerer, but can't see how this would happen. It makes more sense that it would work loose to give play in the headset. I have tried torquing the stem steerer clamp bolts tighter than specified, but am nervous of crushing the carbon steerer tube .
Has anyone encountered such a problem before or does anyone have any ideas? I am at a loss - I have lots of experience with this set up on alloy steerer tubes, but this is my first carbon steerer

Comments

  • neeb
    neeb Posts: 4,473
    Strange! I've certainly had the exact opposite problem myself with a carbon steerer - the headset becoming slightly loose after a certain distance or after going over potholes, despite tightening the stem bolts to the correct torque.

    Do you tighten the headset adjusting cap against the stem after tightening the stem bolts? Although the adjusting bolt shouldn't have any influence on the headset tightness after the stem bolts are tightened, if you did this and the stem also happened to be slipping, maybe it could slip down rather than up...?!?

    First thing to do is to get hold of some tacx dynamic carbon assembly compound. This should cure any slipping of the stem on the steerer.
  • Steve I
    Steve I Posts: 428
    I would have thought it highly unlikely that the stem is coming loose on the steerer. If it was the handlebars would probably not stay at 90 degrees to the front wheel. It sounds like there's a problem with the actual headset itself, maybe it's binding somehow.
  • whyamihere
    whyamihere Posts: 7,715
    Get some Ritchey Liquid Torque and apply it between the stem and steerer, it will sort you out.
  • wilwil
    wilwil Posts: 374
    neeb wrote:
    Strange! I've certainly had the exact opposite problem myself with a carbon steerer - the headset becoming slightly loose after a certain distance or after going over potholes, despite tightening the stem bolts to the correct torque.

    Do you tighten the headset adjusting cap against the stem after tightening the stem bolts? Although the adjusting bolt shouldn't have any influence on the headset tightness after the stem bolts are tightened, if you did this and the stem also happened to be slipping, maybe it could slip down rather than up...?!?

    First thing to do is to get hold of some tacx dynamic carbon assembly compound. This should cure any slipping of the stem on the steerer.

    Same problem. New stem on Saturday all correctly tightened, lose after 15 km on Sunday. I hope there is no damage done.
  • the great cornholio
    the great cornholio Posts: 33
    I can imagine how the stem might "creep" down the steerer tube, without being loose enough to twist. This problem seems to happen after standing on hills, so there may be downward forces on the stem.

    BTW, some people suggest that the steerer bung has no role beyond headset adjustment, but it seems to me that it might also play a role in supporting the steerer against compression from the stem . Does this make sense? Obviously, for this to work, the plug would need to be in the appropriate vertical position within the steerer tube.
  • wilwil
    wilwil Posts: 374
    the great cornholio wrote:
    I can imagine how the stem might "creep" down the steerer tube, without being loose enough to twist. This problem seems to happen after standing on hills, so there may be downward forces on the stem.

    BTW, some people suggest that the steerer bung has no role beyond headset adjustment, but it seems to me that it might also play a role in supporting the steerer against compression from the stem . Does this make sense? Obviously, for this to work, the plug would need to be in the appropriate vertical position within the steerer tube.

    Yes the bung helps stop the carbon steerer from being crushed. Alu steerers only need a star nut.

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