CR1-SL Fork expander bung

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keef66
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CR1-SL Fork expander bung

Postby keef66 » Wed Jul 03, 2013 09:04 am

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?)

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Me-109
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Re: CR1-SL Fork expander bung

Postby Me-109 » Wed Jul 03, 2013 09:26 am

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
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Re: CR1-SL Fork expander bung

Postby keef66 » Wed Jul 03, 2013 09:33 am

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
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Re: CR1-SL Fork expander bung

Postby Gozzy » Wed Jul 03, 2013 10:56 am

Out of curiosity, where did you find that info on the Scott website?

boblo
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Re: CR1-SL Fork expander bung

Postby boblo » Wed Jul 03, 2013 11:20 am

Why do you want the steerer at or above the stem? It usually is cut a few mm below.

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Me-109
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Re: CR1-SL Fork expander bung

Postby Me-109 » Wed Jul 03, 2013 11:44 am

^^ 'Cos it's a carbon steerer, not an aluminium one.

boblo
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Re: CR1-SL Fork expander bung

Postby boblo » Wed Jul 03, 2013 11:57 am

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
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Re: CR1-SL Fork expander bung

Postby keef66 » Wed Jul 03, 2013 12:03 pm

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
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Re: CR1-SL Fork expander bung

Postby boblo » Wed Jul 03, 2013 12:36 pm

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
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Re: CR1-SL Fork expander bung

Postby keef66 » Wed Jul 03, 2013 12:42 pm

Or to just below the top of a 5mm spacer they don't supply...

chris@68
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Re: CR1-SL Fork expander bung

Postby chris@68 » Wed Jul 03, 2013 12:46 pm

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

Bozman
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Re: CR1-SL Fork expander bung

Postby Bozman » Wed Jul 03, 2013 13:05 pm

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
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Re: CR1-SL Fork expander bung

Postby boblo » Wed Jul 03, 2013 13:20 pm

@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?
Last edited by boblo on Wed Jul 03, 2013 14:33 pm, edited 1 time in total.

keef66
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Re: CR1-SL Fork expander bung

Postby keef66 » Wed Jul 03, 2013 13:53 pm

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
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Re: CR1-SL Fork expander bung

Postby chris@68 » Wed Jul 03, 2013 14:29 pm

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!)...

keef66
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Re: CR1-SL Fork expander bung

Postby keef66 » Thu Jul 04, 2013 10:52 am

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
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Re: CR1-SL Fork expander bung

Postby Gozzy » Thu Jul 04, 2013 11:04 am

Add an in-line barrel adjuster?

keef66
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Re: CR1-SL Fork expander bung

Postby keef66 » Thu Jul 04, 2013 11:15 am

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
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Re: CR1-SL Fork expander bung

Postby Gozzy » Thu Jul 04, 2013 23:31 pm

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.

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MrBrightside
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Re: CR1-SL Fork expander bung

Postby MrBrightside » Fri Jul 05, 2013 07:36 am

So where do we stand with slamming the stem?


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