CR1-SL Fork expander bung

keef66
keef66 Posts: 13,123
edited February 2014 in Workshop
Fork bung question for those who have assembled theirs:

I cut the steerer last night to allow for the initial 3 spacers + stem, but when I inserted and tightened the expander bung I found it sits slightly proud of the top of the steerer. Is this correct? If so, I need to trim a bit more off to give me enough space to take up all the play in the headset components.

If this is where it's meant to sit, does that also mean that I shouldn't have a spacer above the stem? (I'm getting a feeling of deja-vu about this; don't Cannondale say no spacers above?)

Comments

  • me-109
    me-109 Posts: 1,915
    First time I did mine it ended up sitting proud of the steerer top by a mm or so, but only noticed that when I subsequently trimmed the steerer again. Second time round it sat flush. Just try undoing it and reseating it. You want the steerer at or above the top of the stem, then a small spacer between the stem and top cap.
  • keef66
    keef66 Posts: 13,123
    Thanks for the quick reply. Just found some info on Scott's website which confirms what you say:

    Expander flush with top of steerer, tighten to 8-9 Nm
    Maximum of 5mm spacer above the stem
    Minimum of 5mm spacer below the stem, maximum 40mm.
    Stem clamp bolts 5-7 Nm, or lower if recommended by stem manufacturer.

    Bit odd that they don't supply any 5mm spacers :roll:
  • gozzy
    gozzy Posts: 640
    Out of curiosity, where did you find that info on the Scott website?
  • boblo
    boblo Posts: 360
    Why do you want the steerer at or above the stem? It usually is cut a few mm below.
  • me-109
    me-109 Posts: 1,915
    ^^ 'Cos it's a carbon steerer, not an aluminium one.
  • boblo
    boblo Posts: 360
    Hmmmm. Doing a quick search, I see this has been debated before. I can't see why you'd need a top spacer just because the steerer is carbon. If you did, Scott would supply one, no?
  • keef66
    keef66 Posts: 13,123
    There seem to be 2 schools of thought with carbon steerers; clamp at the top, and don't clamp at the top. Both are meant to ensure the steerer isn't crushed by inappropriate clamping.

    Cannondale, who insist on no spacers above the stem, presumably because the expander bung sits right at the top of the steerer so that's where they want the stem to clamp. Scott similarly want the clamp within 5mm of the top of the steerer, and their expander bung also sits right at the top.

    Others (who? some fork manufacturers?) insist you don't clamp too close to the end of the steerer, and insist on at least one spacer above the stem. I'm assuming this is using an expander bung which sits below the top of the steerer, so you can position the bung to coincide with the stem clamping area.
  • boblo
    boblo Posts: 360
    That was/s my understanding. So in the case of The Scott CR1 (the point if the OP), the fork steerer is cut to just below the top of the stem. Phew, glad that's sorted :-)
  • keef66
    keef66 Posts: 13,123
    Or to just below the top of a 5mm spacer they don't supply...
  • chris@68
    chris@68 Posts: 22
    keef66 wrote:
    Thanks for the quick reply. Just found some info on Scott's website which confirms what you say:

    Expander flush with top of steerer, tighten to 8-9 Nm
    Maximum of 5mm spacer above the stem
    Minimum of 5mm spacer below the stem, maximum 40mm.
    Stem clamp bolts 5-7 Nm, or lower if recommended by stem manufacturer.

    Bit odd that they don't supply any 5mm spacers :roll:

    How happy am I to have logged in to surf 'recent posts' only to find my questions (CR1 Pro currently on the work stand :) ) all but answered - one thing to double check, please...
    Expander flush with top of steerer, tighten to 8-9 Nm
    am i right in thinking that the 8-9Nm is applied to the 8mm hex socket that is inside the expander assembly and not the 'top cap' that is subsequently tightened to preload the bearing.
    Many thanks
    Chris
    Scott Cr1 Pro
    Cove Handjob
  • Bozman
    Bozman Posts: 2,518
    I read that you need a gap of at least 3mm below the top of stem and the steerer, but I found that the headset was still slack and in the end I had to leave 5mm to get enough preload on the bearings. This wasn't noticeable until you tried the brakes and there was still some movement between the forks and steerer, I guess that the top cap must be quite deep.

    I didn't really want any spacers because the head tube is long enough already but I used a 5mm spacer below the stem and nothing above, going by what folk have put on here I'm glad that I put a 5mm spacer between the headset and stem, I've never had an issue with that before though.

    It's all tip top now and after a couple of rides I've got to say that you can't fault it for the price, bargain... a light bargain at under 16lb built up.
  • boblo
    boblo Posts: 360
    edited July 2013
    @chris. Yes you're right. If you tighten the top cap preload to 8 or 9nm you might just have the worlds first fully rigid (in all aspects) bike :-) The top cap is tightened to juuuust take out any play in the headset, the stem is then tightened and then the top cap can be backed off a smidge.

    Does that make sense?
  • keef66
    keef66 Posts: 13,123
    I found the info in their 2013 bike manual. No mention of this in 2012 or earlier, but maybe they've had some issues so needed to add the info.

    http://assets.scott-sports.com.s3.amazo ... ral_en.pdf

    Page 7 Steerer / stem assembly

    Yes, the 8-9 Nm is for the meaty hex socket in the expander bung itself.

    Interesting to read that someone else has found the customary 3mm clearance is insufficient to remove all the headset play.

    I'm off home shortly to remove the spacer above the stem and have another go with the hacksaw!
  • chris@68
    chris@68 Posts: 22
    boblo and keef - thank-you - makes 100% sense - the bike is now fully assembled and awaiting a short trip to my friendly local garage tonight where I have a loan of a torque wrench to nip-up relevant bolts :)

    eeeee, bring back t'good old days of steel, aluminium and star fangled nuts - in those days my only my only 'specialist' tool was my torque-wrist (patent still pending!)...
    Scott Cr1 Pro
    Cove Handjob
  • keef66
    keef66 Posts: 13,123
    Mine now has no spacer above the stem and the headset is all nicely free from play.

    Anyone got any tips on setting up a triple front mech on a bike with no barrel adjusters? I've followed the Shimano instructions to the letter but I can't get the thing to shift into the big ring, and the cable tension feels too high.
  • gozzy
    gozzy Posts: 640
    Add an in-line barrel adjuster?
  • keef66
    keef66 Posts: 13,123
    I am considering this, but I feel I am getting something more fundamentally wrong here. Maybe I'm getting the cable too tight to start with?
  • gozzy
    gozzy Posts: 640
    I think I've had that problem before. I can't for the life of me remember what I did to get it right, might have been something stupid like not having the shifter in the right gear when tightening.
    I'd go for undoing it, click the shifter up and down, make sure it's in the right gear, then cable up again making sure the cable run is ok. Oh and make sure the derailluer is adjusted vertically properly. If it's none of those then good luck.
  • mrbrightside
    mrbrightside Posts: 214
    So where do we stand with slamming the stem?
  • Bozman
    Bozman Posts: 2,518
    MrBrightside wrote:
    So where do we stand with slamming the stem?

    I just put a 5mm spacer between the headset and the stem, there's no need for anymore due to the relaxed geometry.
  • johnmiosh
    johnmiosh Posts: 211
    I currently have all the spacers above the stem, except for the angled base one. I want to cut the steerer to get rid of all but a single 5mm one. The expander bung feels rock solid; how is it removed without damaging the tube?
  • keef66
    keef66 Posts: 13,123
    johnmiosh wrote:
    I currently have all the spacers above the stem, except for the angled base one. I want to cut the steerer to get rid of all but a single 5mm one. The expander bung feels rock solid; how is it removed without damaging the tube?

    Same way you got it in there; remove top cap and bolt (if fitted) then loosen with an allen key. You might have to give it a good tap to release the expander mechanism. Don't unscrew to the point that the thing falls apart inside the headtube though.
  • Manc33
    Manc33 Posts: 2,157
    Old thread, but I got a bung recently and was confused at first and now I'm not.

    It seems the bung sits on top of the steerer, then you tighten it with an 8mm hex, I am guessing pretty tight, although lets not go all silly, this is carbon!

    Then that bung acts as "the end of your fork", so you have that all 2-3mm under the top spacer, then screw in the normal 5mm hex bolt with top cap in carefully to give compression on the headset bearings as per usual.

    I assume the bung itself has to initially be in pretty tight so you don't make it slip when doing the normal 5mm top bolt.

    Don't quote me on any of this. :P
  • bobones
    bobones Posts: 1,215
    Sounds like you got it. The bung needs to be tight because if not, tightening the top cap will tend to pull it up out of the steering tube. Scott recommended 9NM, which is scarily tight!

    If you've not cut the steering tube short enough to set the preload and can't be bothered fixing it, you can insert a extra spacer below the top cap, set the preload, tighten the stem bolts, remove the top cap and temporary spacer and refit the top cap. :)

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