Slipping stem and steerer

GyatsoLa
GyatsoLa Posts: 667
edited April 2010 in Workshop
I'm hoping someone can give me some pointers to where I'm going wrong:

I just fitted a new longer stem to my bike (threadless headset). A 120mm FSA stem:

http://www.chainreactioncycles.com/Mode ... elID=42437

onto an alu steerer on a carbon (Enigma Etape) fork. The existing (Thomson) 100mm stem works fine, I just wanted to try out something longer.

I tightened the top cap and adjustment bolt as normal, and then tightened the stem bolts - I used a torque wrench to get them to 6 newtons, as indicated on the stem (the torque wrench is brand new, but seems to be accurate, they feel good and tight to the touch and visually the gap looks good).

The problem is that they are not gripping tight enough. The front wheel turns normally, and there is no noticeable play, but if I put any pressure on the wheel the steerer slips through the stem. This occurs even when I tighten the stem bolts as much as I dare (well over the stated max).

Am I doing something wrong, or could the stem be faulty?

Comments

  • rake
    rake Posts: 3,204
    is it definitely the right sized clamp. what is the sleeve in the picture. is that part of it like a shim. other than that people say carbon assembly paste is what you need.
  • GyatsoLa
    GyatsoLa Posts: 667
    Yes, right size - 1 1/8 steerer (31.8), and the sleeve in the picture is on the stem.
  • rake
    rake Posts: 3,204
    all i can think is that reducer shim causing problems, aluminium wont grip at the same tightness as carbon i would have thought. it may also reduce the clamping force to squash the shim to the tube. im guessing here really but i dont like the idea of the shim and axtra slipping surface. i would take the top cap off again while the stem is clamped up and observe which part is slipping, either the shim on the steerer or the stem on the shim. it could give you a clue.
  • GyatsoLa
    GyatsoLa Posts: 667
    rake wrote:
    all i can think is that reducer shim causing problems, aluminium wont grip at the same tightness as carbon i would have thought. it may also reduce the clamping force to squash the shim to the tube. im guessing here really but i dont like the idea of the shim and axtra slipping surface. i would take the top cap off again while the stem is clamped up and observe which part is slipping, either the shim on the steerer or the stem on the shim. it could give you a clue.

    rake thats a good observation you made there. I just tested it with the cap off to see what was happening. The shim is gripping the steering column, but the clamp isn't gripping the shim (even when the bolts are tightened to 6newtons). I guess it must be a manufacturing fault.

    I'll have to assume it is a fault, so unless someone can think of something else I'm doing wrong, I'd better send it back to Chainreaction. I wonder if this is the only one with the problem - its potentially a very dangerous fault.
  • solsurf
    solsurf Posts: 489
    have you checked the expander bolt, I replaced my handlebars and had the same problem as you, in the end I replaced the expander bolt and used carbon paste, now I have no problems.

    hope this helps
  • thel33ter
    thel33ter Posts: 2,684
    You could try rough the shim up with some sandpaper. Not my fault if it fails catastrophically though :wink:
    And now you know, and knowing is half the battle
    05 Spesh Enduro Expert
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  • Down/Up
    Down/Up Posts: 27
    As Solsurf said used some carbon assembly paste, this is exactly the sort of situation its designed for.
  • GyatsoLa
    GyatsoLa Posts: 667
    I never heard of carbon assembly paste, I just googled it and according to the instructions:

    http://www.competitivecyclist.com/road- ... .52.1.html

    .. it seems to be for carbon on carbon only. My clamp and the shim are aluminium. Perhaps loctite would work?

    I checked the expander bolt - its very new and worked fine on the stem I used before so I'm pretty sure that isn't the problem.
  • Carbon assembly paste is suitable for all materials I think.
    It just increases the coefficient of friction between the 2 materials. i.e less likely to slip at the same torque applied to the boilts.

    Think of it as the opposite to grease/lube

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  • GyatsoLa
    GyatsoLa Posts: 667
    Thanks for the feedback. I'll see if I can guy some carbon paste - if not, then I'll send the clamp back to CRC, I don't think this issue is acceptable on such a safety critical item. If something is clamped to its torque, its not unrealistic to expect it to stay clamped under normal use.
  • Have you got small spacers between the bolt clamps to prevent over crimping? When i received my Focus Cayo which has the same stem i encountered the same problem basically because the small spacers wouldn't allow me to tighten enough. Spacers removed, tighten a little more and it's held no problem without over-torquing.
  • GyatsoLa
    GyatsoLa Posts: 667
    Have you got small spacers between the bolt clamps to prevent over crimping? When i received my Focus Cayo which has the same stem i encountered the same problem basically because the small spacers wouldn't allow me to tighten enough. Spacers removed, tighten a little more and it's held no problem without over-torquing.

    Thanks for pointing that out - I hadn't noticed there was a spacer there (there was one on the lower bolt hole) I removed it and yes, it works! It is holding tight. Unfortunately, there is a sign of slight crimping - the two flanges at the bolt are touching, which according to my Big Blue Book indicates overtightening - but the torque setting is right. Oh well, it seems to work, although I still think there is a slight problem with it. Unless of course I was supposed to remove that spacer all along, in which case its a but of a d'uh moment for me.....