Fitting a top cap expander bung thingy

bartman100
bartman100 Posts: 544
edited January 2014 in Workshop
Can anyone point me to an idiots guide to re-fitting one of these? It's one of those top caps with bung like this:

deda-exp-bung-med.jpg?w=350&h=350&a=7

I cannot get it to fit in the steerer without loads of play in the headset. Is it good practice to tighten top part of bung to the smaller bottom part before putting in steerer? Or leave loose then tighten when in situ? Can't seem to tighten it all up once in place.

Comments

  • majormantra
    majormantra Posts: 2,094
    Should be fully assembled but loosened when you push it into the steerer. Carbon compound may help it stay put. Then tighten it up. Then assemble remained of headset. You must make sure the top cap isn't bottom out on the bung. If it is the headset will never work without play and will wear prematurely.
  • sungod
    sungod Posts: 17,182
    the same one is sold under a few brand names

    in a nutshell, expander/steerer should be free of grease or cutting dust etc.

    the knurling is quite sharp, so it grips well, 5-6Nm on the hex key to expand it is plenty

    follow the fork manufacturer's advice for the fork length, they vary, personally i'd cut near flush with the top of the stem, add the plug, then use a thin spacer on top to ensure the underside of the topcap doesn't foul on the expander, but there are other schools of thought, some cut higher, some lower
    my bike - faster than god's and twice as shiny
  • PhunkyPhil
    PhunkyPhil Posts: 143
    I bought one of these and it was a real pain to get into the frame. The first part would go in easy but it would expand the upper part. I tried to tighten\loosen the screw and the thing fell apart a few time and I had to put it all back together.

    In the end it went in. I think I undid the screw as much as was physically possible without it falling apart and then slowly putting in.

    Once in it works fine.
    http://veloviewer.com/SigImage.php?a=116373&r=3&c=5&u=M&g=p&f=abcdefghij&z=a.png
  • sungod
    sungod Posts: 17,182
    on steerers with slightly thicker walls, some bungs are hard (or impossible) to fit, this is one of them!
    my bike - faster than god's and twice as shiny
  • Manc33
    Manc33 Posts: 2,157
    Got the same one as OP, you can loosen it so theres 3 threads on the bottom on the inside, after that you're risking it all falling to pieces. :lol: It should go in when its that loose. Mine goes in my Stelvio fork easy enough.

    I couldn't understand how to fit it until I realized it is a 2 stage thing.

    1. Tighten the bung with an 8mm hex.
    2. Tighten 5mm top bolt to compress headset.

    I was thinking you tighten just one thing. :oops:

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