[Closed] Stem slippage on carbon steerer - User or Equipment error?

The steerer bung is just for preloading the headset, so won't help the stem. Are you torquing the stem to the values on it?

Carbon steerers are supposed to have some steerer above the stem (hence spacer). Also best to have a large bung that supports the inside of the steerer for the whole clamping area.

look at the depth of your ahead cap, that could be bottoming out on the steerer bung so the headset is never really tight, although a bit of spacer above the stem is a good idea on a carbon steerer and should stop this

the steerer bung just being for preloading the headset and it's the stem tightness that keeps everything in place is an idea that only works on the internet, i've had plenty of instances where the headset's become loose over time as the stem has crept up because the steerer bung has vibrated up, so check that

If the top of the bung has a slightly larger diameter than the steerer then the stem will be tightening on that. Move the stem down so that the top of the steerer is above it by a few mm. Fit a spacer that's a couple mm more than that.

The stem is being tightened to 5nm, checked with two torque wrenches.

Maybe the cap is bottoming out, I don't think it is, as everything seems very tight when loaded?

I didn't know that you're supposed to have a spacer above the stem. Okay so the new steerer bung is a lot longer, so I'll adjust the spacers.

Thanks guys, I knew it would probably be user error!! 😳

you are tightening the stem after the headset is preloaded, aren't you?

I'd swap one of the spacers you have under the stem to above and maybe add another 5mm below and see how you get on.

I had a lot of problems on an on-one 456 carbon - the headset was constantly coming loose. I never really got to the bottom of why but switching to a Hope headset solved it so I assume there was movement within the headset components themselves that was causing the issue.

Yeah;
Steerer bunger in and tighted to spec (8nm from the top of my head)
Stem on lose
Cap on and tightened to 3nm??
Stem tightend to 5nm

I'm only using this: http://www.wiggle.co.uk/lifeline-compression-plug-with-alloy-cap/

So i'm hoping the new one, along with the spacer change, will result in it staying put.

Isn't the BBB bung just the same type?

I prefer something like the Deda

http://www.wiggle.co.uk/deda-expander-bung/

wonder if you're actually tightening the stem against the top of the bung rather than the steerer tube itself?

Lifeline:
[IMG] ?w=430&h=430&a=7[/IMG]

BBB:
[IMG] http://media.chainreactioncycles.com/is/image/ChainReactionCycles/prod29884_Black_NE_01?wid=500&hei=505 [/IMG]

Knurls looks more substantial and goes down further so will provide more support when I place a spacer above the stem?

Do you guys also add carbon paste to the bung? (obviously not the stem)

I add a bit of carbon paste for good luck, no reason to really.

Are you fitting it correctly? You need to tighten the bung, usually with a 6mm Allen key before you fit the top cap, otherwise everything will come loose. Fitting the top cap alone will make it seem tight, but it'll all come loose in no time.

Yeah;
Steerer bunger in and tighted to spec (8nm from the top of my head)
Stem on lose
Cap on and tightened to 3nm??
Stem tightend to 5nm

I'll add a drop of carbon paste too then for good measure!

I did see you'd said that, but just wanted to be absolutely certain, it is a bit counter intuitive!

Cap on and tightened to 3nm??
Stem tightend to 5nm

I cannot recall seeing a specific recommendation for the amount of torque when tightening the top cap to load the headset bearings. I generally tighten the top cap progressively and rock the bike gently back and forth with the front brake on to check when loosenesss/play in the bearing disappears as a starting point, usually tightening a little bit more from that point whilst checking that the steering still feels smooth by rotating the bars, before then tightening the stem bolts.

Note that the torque values quoted by the manufacturers for stems/bungs are usually [u]maximum[/u] values.

It doesn't help that there appears to be some variation/inconsistancy in the guidance published by different manufacturers, e.g. Deda specify no spacers above the stem, whereas Trek specify a 5mm spacer above the stem.

Trek/Bontrager detailed a few years ago what they considered essential for stems used with carbon steerers in this document:

[url= http://www.bike-manual.com/brands/trek/om/assets/pdfs/BT10%20ca_steerer_stem%200701PN.pdf ]Trek Service Information issued in 2010 for stems and carbon steerers[/url]

which was referred to in the cycling press following a catastrophic failure involving a road racer in the USA (see links below). I suspect the failure was caused by incorrect installation, such as way overtightening the stem bolts, rather than (as Trek suggest) a flawed stem design, but even so Trek's guidance concerning suitable stems and installation does seem to make good sense to me.

http://velonews.competitor.com/2010/06/news/steered-wrong-racers-concerned-about-broken-carbon-steerer-tubes_121389

http://www.bikerumor.com/2010/06/23/broken-trek-carbon-steerer-tubes-result-of-the-wrong-stems/

Interesting articles - thanks for that!

Yeah it was Dedas instructions, included with the stem, that I was following during the build.

The BBB arrived yesterday and looks meatier, so I'll get everything sorted tonight and report back if it stays put/slips again.

Thanks all for your advice!

Haven't got around to fitting it yet but noticed this:

[IMG] [/IMG]

Carbon Assembly Paste

Always use with carbon. The low spec torque will be more likely to avoid slipping then. Often manufacturers specify use of paste as mandatory with carbon components.

Worth using with ali also. Carbon + ali especially as they tend to react and bond. The paste will act both as grip and help prevent the bonding.

@deadkenny you're referring to the bunger right?

The Stem instructions may differ from the fork instructions.
The fork instructions may insist that the steerer extends above the stem, with a spacer above the stem to provide clearance for preloading. The fork instructions may also specify the types of steerer bung required to support the steerer from being deformed by the clamping forces from the stem.

nathb - Member 
@deadkenny you're referring to the bunger right?

Paste between stem and steerer. Just smear the stuff on the steerer before fitting the stem.

It's the stem that holds it all in place. Bung (and star nuts for ali steerers) just pull the thing up. The stem could still slip. Carbon paste helps prevent it slip and reduces torque required so less likely to damage the carbon.

I would have assumed that carbon paste should be used on the steerer where the stem clamps around it, but it seems not. Both Trek and Specialized for example state that carbon paste should not be used, as explained here:

http://thegoldenwrench.blogspot.co.uk/2011/09/tech-bulletin-from-trek-regarding.html

Often manufacturers specify use of paste as mandatory with carbon components.

Do they? I've never personally seen that. The stuff didn't exist 5 years ago after all!

njee20 - Member 
Do they? I've never personally seen that. The stuff didn't exist 5 years ago after all!

Easton do. Instructions mentioned it for both my carbon bars and from what I remember surprisingly the alloy seat post I had. From above link it looks like Trek also used to recommend it, but not now. Though they didn't say it must be used. I recall Easton did. Though as I say that was for bars and posts.

Carbon and carbon paste on bikes have been going much longer than 5 years too.

slowster - Member 
I would have assumed that carbon paste should be used on the steerer where the stem clamps around it, but it seems not. Both Trek and Specialized for example state that carbon paste should not be used, as explained here:
> http://thegoldenwrench.blogspot.co.uk/2011/09/tech-bulletin-from-trek-regarding.html

Interesting. I see their point I guess, especially when the headset is loose, though it's probably a caution from lawyers.

Ignore my advice then. No paste. Just don't over torque. You may still get slippage on the stem.

Personally I'd "steer clear" ( 😀 ) of carbon steerers.

User error it is!

Normally I undo the cap, then stem and finally the bunger. This evening I undid the cap followed by the bunger - low and behold it was stuck. Meaning that the steerer was clamping on to it! 😳

Anyway the new bunger is in and is much longer than it's predecessor:
[IMG] [/IMG]

I also added a dab of carbon paste on the bunger too.

Looks a little strange with a spacer above ❓
[IMG] [/IMG]

Thanks for all your advice folks!

Carbon and carbon paste on bikes have been going much longer than 5 years too.

I exaggerate slightly, but it is a recent invention. Definitely last 10 years. Pace first did it IIRC, then Tacx soon after.

From above link it looks like Trek also used to recommend it, but not now

Not really, it used to say "use it on carbon parts if you want", it now says "use it on Carbon parts (other than steerers) if you want". I'm not a massive fan of it to be honest. Still assemble most stuff dry.

I'm not a massive fan of it to be honest. Still assemble most stuff dry.