Steerer compression plug slipping
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  1. #1
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    Steerer compression plug slipping

    New bike new bike finally arrived - Pinarello Prince Disk. Put the pedals on and then the bars on and checked torque on bolts and tested up and down the street. Happy days!

    2nd ride in, I started getting a popping in the front end when hard braking. Then when yarding on the handlebars. Getting worse through out the ride. Afterwards I check the headset for movement and sure enough with some effort, there is movement.

    Long story short, the underside of the stem cap has a raised area that extends down into the stem, and the compression plug which has a cap that sits on top of the steerer, has about 1mm of space to the top of the stem. When I tighten the cap it appears it's bottoming out against the compression plug.

    I cut the steerer down another 1.5mm to allow room so the cap and plug do not contact. Now when I start to tighten the stem cap to it's rated 6Nm, compression plug it slips and pulls up to the cap starting at about 3-4Nm. The plug is marked as max 8Nm and it tightens to that mark fine. I tried assembly compound in the steerer but that seemed worse than with it dry.

    Anything I'm missing here? The only thing I can think of is I used a damp paper towel in the steerer to catch the carbon dust and I also used windex spray on the guide to help make a wet cut to keep carbon dust down. I cleaned and dried the inside of the steerer with an alcohol soaked rag before the last assembly attempt. There is no visible damage or cracking to the steerer that I can see when tightening the plug to 8Nm.

    Any advice from the RBR brain trust?

  2. #2
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    Use a different compression plug.

  3. #3
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    Take the comp plug out, use some iso alcohol and clean any grease/oil out of the tube. Then take some fine emery cloth or wet & dry sandpaper and sand lightly the inside of the tube, just to roughen the surface a little. I bet that will solve your slipping issue.
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  4. #4
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    Quote Originally Posted by duriel View Post
    Then take some fine emery cloth or wet & dry sandpaper and sand lightly the inside of the tube, just to roughen the surface a little.
    Good suggestion. You could also try to sand the surface of the compression plug if you feel squeamish about sanding the steerer. That way if it doesn't work, you're only out the cost of the plug.

  5. #5
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    Quote Originally Posted by tinball View Post
    Now when I start to tighten the stem cap to it's rated 6Nm, compression plug it slips and pulls

    That's at least part of the problem (unless you have some new fangled headset I'm not familiar with).

    That should be tightened "as necessary" to get proper adjustment and 6Nm is WAY more torque than should be necessary to get the proper adjustment. It's probably a good thing your plug slipped because 6Nm on the top cap probably would bind your bearings.

    You should be using 'as little as possible' torque to eliminate play and that's likely no where near 6Nm or even 3 for that matter. Again unless you have some not normal headset I'm not familiar with.

  6. #6
    tlg
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    Quote Originally Posted by Jay Strongbow View Post
    That should be tightened "as necessary" to get proper adjustment and 6Nm is WAY more torque than should be necessary to get the proper adjustment. It's probably a good thing your plug slipped because 6Nm on the top cap probably would bind your bearings.

    You should be using 'as little as possible' torque to eliminate play and that's likely no where near 6Nm or even 3 for that matter. Again unless you have some not normal headset I'm not familiar with.
    ^^^ This.
    You shouldn't be 'targeting' 6Nm. That's a MAX to prevent damage.


    Also, is this your Pinarello expander? All the pictures I find show it's smooth. If so, looks like a sh!tty design. Any expander I've ever had has a knurled texture and grips like a sumnofab!tch.

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    That's the one. The other element in this whole thing is that the stem is likely also slipping. It's a compression/'wedge type and not a clamp type. See the pic below. That is likely a component of the slippage as well. The compression plug starts slipping at 3-4Nm according to 2 different torque wrenches - well short of 6Nm.

    Steerer and stem


    Top cap

  8. #8
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    Quote Originally Posted by tinball View Post
    That's the one. The other element in this whole thing is that the stem is likely also slipping. It's a compression/'wedge type and not a clamp type. See the pic below. That is likely a component of the slippage as well. The compression plug starts slipping at 3-4Nm according to 2 different torque wrenches - well short of 6Nm.

    Steerer and stem


    Top cap
    Like others have said, you shouldn't need to torque to anywhere near that, in-fact I've never used a torque wrench on a top cap because I would never get close to the limit. Just tighten till there is zero play in the fork when you push the bike back and forth with the front brake locked then add a little, and quit and tighten the stem down.
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  9. #9
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    I have found FSA ones to work well.

    https://www.jensonusa.com/FSA-Compre...ug-and-Top-Cap
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  10. #10
    tlg
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    Quote Originally Posted by tinball View Post
    That's the one. The other element in this whole thing is that the stem is likely also slipping. It's a compression/'wedge type and not a clamp type. See the pic below. That is likely a component of the slippage as well. The compression plug starts slipping at 3-4Nm according to 2 different torque wrenches - well short of 6Nm.

    Steerer and stem


    Top cap
    There are no pics to be seen.

    You should probably just take it to a professional. They will tighten the top cap without a torque wrench.
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    Strange the pics where in the preview and post initially.

    Anyway, I have it sorted (I hope). A local bike shop had a Specialized compression plug on hand. It was much more aggressively textured. Was able to tighten the top cap to 6. I actually backed it off and re-tightened it to 5Nm. Added some assembly compound to the wedge in the stem and assembled from there. Testing with some sprints to hard braking and a sprint up a steep (10%) ramp didn't yield any movement or popping.

    I will try the image one more time of the stem here...

  12. #12
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    U tightened the top cap to 5Nm? Does the fork still rotate freely?
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  13. #13
    tlg
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    Quote Originally Posted by tinball View Post
    I actually backed it off and re-tightened it to 5Nm.
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    Yes it does move smoothly and freely with no binding. However based on everyone's concern I will definitely reverse course and tighten by hand to just snug with no movement in the headset and give it a run tomorrow. The last thing I want to do is damage the bearings or seats.

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    You know you do the top cap before the stem, right? I'm surprised 6 Nm didn't bind the bearings. Tightening the stem first might explain that.

    You tighten the cap first to adjust the pre-load and not according to any particular torque but by using the minimum pressure required to eliminate play. Then you tighten the stem to lock that adjustment in place with the stem.

  16. #16
    tlg
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    Quote Originally Posted by Jay Strongbow View Post
    You know you do the top cap before the stem, right? I'm surprised 6 Nm didn't bind the bearings.
    Me too. 6Nm will put about 1,100lb axial load on the bearing. 5Nm about 950lb.
    Both exceed the static (radial) load rating of the bearing. The axial load is even less.
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  17. #17
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    Quote Originally Posted by tlg View Post
    Me too. 6Nm will put about 1,100lb axial load on the bearing. 5Nm about 950lb.
    Both exceed the static (radial) load rating of the bearing. The axial load is even less.
    This is ridiculous! .. better check your calc's or figures.
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  18. #18
    MDM
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    Steerer compression plug slipping

    Take it to the bike shop to sort it out.

    I'm confused why you would cut your steerer tube down. Didn't you have a spacer above the stem that you could have swapped for a larger one? Having the top of the steerer tube below the top of the stem is not recommended, at least by Trek. You can pinch the top of the steerer tube when the stem bolts are tightened and thus cause a crack in it. I think Trek recommends a 5 mm spacer above the stem.
    Last edited by MDM; 07-14-2020 at 06:49 AM.

  19. #19
    tlg
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    Quote Originally Posted by duriel View Post
    This is ridiculous! .. better check your calc's or figures.
    Figures are fine. Better check your figures.

    F=T/cD
    5000N (1124lb) = 6,000N-mm/.2*6

    Or use a calculator
    https://www.engineersedge.com/calcul...orque_calc.htm
    Bolt Load Calculator | An easy to use online tool from Riverhawk

    How about a chart?
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  20. #20
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    Your going to propose that if I tighten a steer tube top cap nut to 6 N-m, that this translates to 1000lbs of force axially? ... insane!
    6Nm=4.43 ft-lbs
    You posted a formula with a bunch of variables....
    Please identify what the variables are and their units of measure...
    F:
    T:
    c:
    D:
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  21. #21
    tlg
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    Quote Originally Posted by duriel View Post
    Your going to propose that if I tighten a steer tube top cap nut to 6 N-m, that this translates to 1000lbs of force axially? ... insane!
    6Nm=4.43 ft-lbs
    You posted a formula with a bunch of variables....
    Please identify what the variables are and their units of measure...
    F:
    T:
    c:
    D:
    Feel free to show your work. I provided MULTIPLE sources.
    Look right there in the chart. Only 4.51Nm = 3864N Axial. That's 868lbs.


    It's a very common formula. The basis of the calculators I provided.
    T = c F d (also T = K D F)
    where

    T = torque
    c = coefficient
    F = axial bolt force
    d = nominal bolt diameter


    So.... show your work.
    Last edited by tlg; 07-14-2020 at 12:59 PM.
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  22. #22
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    UGH, I don't know why the pictures keep disappearing. The last post also had a pic that was showing (at least in my browser) last night before I signed off.

    Quote Originally Posted by Jay Strongbow View Post
    You know you do the top cap before the stem, right? I'm surprised 6 Nm didn't bind the bearings. Tightening the stem first might explain that.

    You tighten the cap first to adjust the pre-load and not according to any particular torque but by using the minimum pressure required to eliminate play. Then you tighten the stem to lock that adjustment in place with the stem.
    Jay, yes I do know that you do not tighten the stem before the top cap to preload the headset bearings prior to tightening the stem and the stem is what holds everything together at load/compression.

    Being inexperienced, I couldn't find any published specific torque amount for the top cap and figured if could go up the printed amount provided it didn't bind the headset - which didn't appear to. I guess I figured (incorrectly) that I could use the top cap to reinforce the stem to prevent the the whole system loosening.

    Since then, I have removed the stem, thoroughly cleaned the outside of the steerer with alcohol, applied assembly paste to the compression wedge in stem stem (not the steerer compression plug). Tightened the top cap snugly to where I couldn't get movement when holding the brakes and moving the bike back and forth. This is approximately 2-3Nm according to the bar torque wrench I have. That and the new steerer compression plug I hope should do the trick.

    Quote Originally Posted by MDM View Post
    I'm confused why you would cut your steerer tube down. Didn't you have a spacer above the stem that you could have swapped for a larger one?
    The top cap recesses into the stem by about 1mm. There was about or just over 1mm space below the top of the stem with the original steerer compression plug. When the slippage occurred the plug would be lifted just a bit off the top of the steerer. Mind you this was with the stem bolts torqued to just below or at max 6Nm. Checking with both Zin's and Park Tools books, 3-5mm below the top of the stem is recommended. I cut off approx 1.5mm (I cut off a .75mm piece and the blade thickness is about .75 as well) to get just a bit more room as I initially thought the cap was contacting the steerer and preventing enough preload on the headset. They do mention that it is recommended to leave a spacer above the stem with carbon steerers. But that isn't an option unless I get more flexible (which I am working on) as it was already set to the highest position with no spacer above the stem. Still I may drop it down 10mm which is the smallest size spacer on the stem or order a 5mm one.

    https://www.excelsports.com/assets/gallery/111526-1.jpg

    Since I can't for some reason post images here right now, here is a link to a picture of a carbon version of the stem that comes with the bike. It has compression wedge at the back instead of similar clamp style stems. Also the airfoil shape at the back is the shape of all the spacers so no basic 1 1/8" spacers.

    I want to say thanks to you all for the feedback and helping me learn more about headsets. And thanks CX for not blasting me again! I hope this works out and has solved the issue. I'll know more after tonight - while it's the World's night here, I'll be going solo (damn COVID) but should be able to give it a good testing....
    Last edited by tinball; 07-14-2020 at 01:02 PM.

  23. #23
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    Oh and almost forgot.

    Here is a older but seems relevant video about steerer compression plugs from Luescher Teknik


  24. #24
    sdm
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    I have the same issue on a new Penny Grevil. I took mine back to the shop just to see if my mechanic skills were poor (they're not). Long/short is the stock plug is garbage. I replaced mine with an FSA and haven't had any slippage issues. Would have preferred putting a Specialized plug in as they are the most robust IMO, but they are .5mm to big and wouldn't slide in the steerer without using a hammer. Het.yourself a new plug and make sure there is no grease or oil inside the steerer tube when you instal.it. the 6nm conversation is interesting, but I agree with the consensus that it's not a goal just a max setting. Tighten till there is no play (about 2nm in most cases) then used some carbon paste and torque the stem and you should be fine.

  25. #25
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    As much as I hate Specialized their carbon steerer tube plug design is brilliant. Time’s “quickset” system eliminates the need for the idiotic plug. That’s true brilliance, and a whole other story.

    https://www.amaincycling.com/special...caAqOKEALw_wcB
    Last edited by Notvintage; 07-23-2020 at 09:55 AM.

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