Headset is coming loose after ride bin the bung? Star nut?

sigorman85
sigorman85 Posts: 2,536
edited July 2014 in Workshop
I have a Planet X super light pro carbon and the head set is coming loose after a ride/rides I can't over tighten it because of the obvious and when I do tighten it I'm pulling the bung up through the steerer tube... What's going wrong here? Also I've herd star nuts are better than the head doctor bung things also could it be the bearings in the fork that joins to the head tube? If known what bearings I need can someone let me no many thanks

Si
When i die I just hope the wife doesn't sell my stuff for what I told her I paid for it other wise someone will be getting a mega deal!!!


De rosa superking 888 di2

Comments

  • nicklouse
    nicklouse Posts: 50,675
    Sounds like you are not installing it correctly.

    You do not say what the steerer is made from.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • sigorman85
    sigorman85 Posts: 2,536
    Sorry it's full carbon .... I've pushed the spacers down and stem and tightens the top cap up and then the stem bolts but there is still movement vertically more than lateral also when doing the top cap up on the stem it's pulling the bung up
    When i die I just hope the wife doesn't sell my stuff for what I told her I paid for it other wise someone will be getting a mega deal!!!


    De rosa superking 888 di2
  • mr_evil
    mr_evil Posts: 234
    Check the manufacturer's spec for the bung, and I'm sure you'll find it needs to be done up much tighter than you have it. Don't use a star nut in a carbon steerer, because it damages the fibres.

    Also, use some carbon paste between the steerer and stem.
    https://mrevil.asvachin.eu/
  • nicklouse
    nicklouse Posts: 50,675
    sigorman85 wrote:
    Sorry it's full carbon .... I've pushed the spacers down and stem and tightens the top cap up and then the stem bolts but there is still movement vertically more than lateral also when doing the top cap up on the stem it's pulling the bung up
    So how did you tighten the bung? Sounds like you have not done so.

    And as above carbon steerer means you can only use a bung. A star nut with damage the steerer enough go make it possibly fail.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • lapavoni10
    lapavoni10 Posts: 146
    The bung (or star nut) does not do too much once the stem is tightened. Its primary role is to pre-load the headset prior to tightening the stem bolts. I await chatisment from those more knowledgable :)
  • mitchgixer6
    mitchgixer6 Posts: 729
    That is indeed correct. Once the bearings are loaded correctly and the stem bolts are tightened you could take the bung (and top cap) off with no I'll effects.

    I think the problem here is however that the bung is so loose that the bearings can't be loaded correctly. Definitely check you have the bung tightened inside the tube.
  • patrickf
    patrickf Posts: 536
    Sounds like the expander isn't tightened enough if it's pulling out of the steerer.

    For reference, the instructions for my Scott state that the expander bung should be tightened to 8-9NM.

    Perhaps try a little carbon assembly paste on the outside of the bung before you stick it in the steerer?
  • ugo.santalucia
    ugo.santalucia Posts: 28,312
    IME if the carbon steerer, the bung and the stem are not a good match, you can do all the things they advise you to do and it will still come loose 50 miles later.
    In my case I found no solution and a cracked steerer ended up being a blessing, as I replaced the fork with one with an alloy steerer which has never come loose
    left the forum March 2023
  • dennisn
    dennisn Posts: 10,601
    lapavoni10 wrote:
    The bung (or star nut) does not do too much once the stem is tightened. Its primary role is to pre-load the headset prior to tightening the stem bolts. I await chatisment from those more knowledgable :)

    You are correct.
  • sigorman85
    sigorman85 Posts: 2,536
    Done the pre load and done it up tight...and with in 15 miles there was slight play again!! Argh
    Shall I check for a crack in the steerer tube?:-(
    When i die I just hope the wife doesn't sell my stuff for what I told her I paid for it other wise someone will be getting a mega deal!!!


    De rosa superking 888 di2
  • mr_evil
    mr_evil Posts: 234
    sigorman85 wrote:
    ...done it up tight...
    How tight is that? Are you using a torque wrench? Did you use carbon paste?
    https://mrevil.asvachin.eu/
  • lapavoni10
    lapavoni10 Posts: 146
    Is it a new frame, has everything being faced properly? The headset is seated correctly in the frame and on the forks? Its not just crushing paint as it settles?
    If there are two bolts on your stem (probably), are you pinching them up alternately and torqueing them down as you go?
  • ugo.santalucia
    ugo.santalucia Posts: 28,312
    The only solution is a fork with a metal steerer. If you have a 1 and 1/8 steerer, a Columbus Tusk costs 80 quid and it's an awesome fork

    'nuff said
    left the forum March 2023
  • rolf_f
    rolf_f Posts: 16,015
    ugo.santalucia wrote:
    The only solution is a fork with a metal steerer.

    If that is the only solution then, by definition, there are no Planet X super light pro carbons with their original forks without loose headsets....... :wink:
    Faster than a tent.......
  • ugo.santalucia
    ugo.santalucia Posts: 28,312
    Rolf F wrote:
    If that is the only solution then, by definition, there are no Planet X super light pro carbons with their original forks without loose headsets....... :wink:

    Don't distort, you spin doctor...

    What I said is that if you have that problem (which is by no means a problem of all fork/stem/bung systems) the best solution id to get rid of the problem... hence metal steerer/stem/star nut which always works.

    I had that problem, I have tried all of the above solutions, none worked... I got an alloy steerer, end of the problem
    left the forum March 2023
  • Ouija
    Ouija Posts: 1,386
    A common mistake is that people think tightening the top cap expands the bung. It does.... but only after it's pulled it up the sides of the steerer tube. The bung needs expanding long before the top cap and bolt goes anywhere near it (usually with the next size up allen key in the hole the top cap bolt passes through).

    If you've succesfully preloaded the headset so that the fork doesn't rock back and forth and then it's gone after 15 miles this a problem with your STEM, not the bung. As mentioned elsewhere in this thread, the bung is only to PRE-load the headset bearings, not to maintain the load on the bearings indefinately. That's the job of the stem after you've tightened the bolts up. The tightened stem obviously isn't maintaining the load on the bearings and sliding back up the steerer, pushing the bung up with it.
  • The Mechanic
    The Mechanic Posts: 1,277
    Are you using a torque wrench to tighten the stem bolts? I have a Felt Z4 and have just done 1000 miles Dover to Durness on it. Carbon steerer, alloy stem, no loosening of the headset. Not having a carbon bike before I got myself a torque wrench. When I used it I was a bit taken aback at how tight 5-7Nm was. It was much tighter than I would have done up the stem bolts without a torque wrench. This may not be your problem but worth consideration, unless you have done so already.
    I have only two things to say to that; Bo***cks
  • patrickf
    patrickf Posts: 536
    ugo.santalucia wrote:
    The only solution is a fork with a metal steerer. If you have a 1 and 1/8 steerer, a Columbus Tusk costs 80 quid and it's an awesome fork

    'nuff said
    Careful now, a quick look on Planet X for £80 you get the Columbus Tusk Light Carbon fork.

    While I'm sure it's a great fork, it does appear to have a carbon steerer - although it has an aluminium crown.
  • g00se
    g00se Posts: 2,221
    Something else to consider...

    Check the profile of the bottom of the top cap. If you do not have enough overlapping depth of spacers over the steerer, then the chamfer on the top cap can touch the top of the steerer before the outside of the top cap comes into contact with the spacer. so effectively, you're tightening down on the steerer and pulling the bung out - rather than pushing down on the spacer.

    If this happens, you'll notice that as you tighten the top cap, it'll suddenly stiffen but then stay at that torque. If you're right, it'll progressively stiffen quickly.
  • mulletmaster
    mulletmaster Posts: 502
    Pretty sure my cervelo s5 had a carbon steerer and used a star nut? Of no use to the OP obviously.
  • g00se
    g00se Posts: 2,221
    The Cevelo - which is a 3T fork I believe - uses a thin walled carbon steerer with a short aluminium sleeve that is glued inside the steerer - with the star nut fitted in this.

    2012-3T-Luteus-disc-brake-cyclocross-fork-install-insert03.jpg
  • rolf_f
    rolf_f Posts: 16,015
    ugo.santalucia wrote:
    Rolf F wrote:
    If that is the only solution then, by definition, there are no Planet X super light pro carbons with their original forks without loose headsets....... :wink:

    Don't distort, you spin doctor...

    Wasn't distorting. My point is that unless there is a specific, individual problem with either the fork or the bung then a new fork shouldn't be necessary if the basic design works (ie other people have the same bike, the same fork and the same bung and no problems with it). What's needed is to determine if there is anything wrong with any component or if there is a user error issue before chucking money at the problem.

    Personally I'd just go in search of local expertise and get their advice. I can think of plenty of people round my area who I'd ask before I resorted to buying new stuff.
    Faster than a tent.......

Categories