nasty crack sound from headset area when going over bump

ben-----

A couple of times now I've hit a bump in the road, ones which I should have avoided but on the other hand weren't *that* bad. When I hit them there was a really nasty crack sound from the headset area, I think. I don't think anything's broken but the sound was much more serious sounding than I'd expect. I'm wondering what might be wrong? Is there something I should adjust?

The only messing with the headset area I've done is undone the handlebar stem clamps, which clamp to the fork area, and then tightened up the top cap a little bit. Then tightened the stem clamps back up (to roughly 6Nm). The headset isn't loose (no rattling), nor too tight (handlebars turn fine).

It's on a Cannondale Supersix.

Thanks.

mr_evil

Even though it doesn't rattle, it might still be too loose. Tighten the top cap up until it binds, then loosen it just a tiny bit from there.

ugo.santalucia

As above, tighten it. If it still does it, then inspect the steerer, mine was cracked when it started to make knocking sounds

clickrumble

I had this on my bike, it took me a while to work out that it was my waterbottle moving in the carrier and hitting the frame.

Monty Dog

IME it's usually down to the bars rotating downwardsslightly in the stem due to the impact - sounds a lot worse that it is.

ben-----

Thanks for the replies.

Haven't dealt with this properly yet but It does appear there is some damage :







I notice now, that there is quite a distance between the top of the steerer/forks tube up to the top of the stem clamp. Maybe I should remove one of the plastic spacers to lower the stem clamp.

ugo.santalucia

That's not the problem, I would say... just a tiny dent, not a crack

Matthewfalle

Should be a 5mm or so gap between the top of steerer and headset preload adjuster bolt, either by use of a spacer or just the height of the stem itself.

ben-----

OK thanks.

> Should be a 5mm or so gap between …

Like so?:



Trying to "Tighten the top cap up until it binds, then loosen it just a tiny bit from there" I've managed to get the cone (or wedge, is probably a better description) (marked with arrow) stuck to the cap:



I can't get it off at the minute. Blimey.

balthazar

I think you have that wedge upside down. The chamfered face should meet another chamfered face in the black cylinder component, which (should be split lengthways) such that when you tighter the bolt against load the black part expands and wedges into the steerer tube. If this isn't clear, maybe check the Park Tools site or some youtube videos to see how this all works. It really isn't obvious, and if you don't assemble it right you will have annoying problems forever.

The slight damage in the first picture looks to be the result of a little over tightening, not fatal. I think Monty had it right: bars rotating downward crack loudly, and you may not notice the change.

ben-----

> I think you have that wedge upside down.

No, it's definitely the right way round there. I got it off using a metal vice. It was through total ignorance of the system that resulted in me getting it stuck like that in the first place.

It's one of these types: http://www.jarredscycling.com/2013/08/t ... adset.html

A main thing which I didn't realise is (I'm completely new to threadless headsets although I don't think this is a particularly normal/standard one), there are two allen key nuts in one as it were -- down the stem. One 5mm which handles the expander (tightens the two wedges together pushing out the expander) and a 6mm one which is the top cap. And you have to get the expander bit inline with the bottom stem clamp -- that's what the bottom stem clamp clamps round.

One thing I'm not understanding is tightening the top cap doesn't seem to effect the stiffness of the handlebars turning. I haven't put a lot of force on it but tightening it doesn't result in the handlebars not turning so easily.

Anyway, got it all back together now. Hopefully all will be well. Thanks.

Matthewfalle

Yup - that stem/steerer gap is perfect.

To tell the truth, steerer damage looks like nothing to worry about either.

stanthomas

ben----- wrote:

> Should be a 5mm or so gap between …
Like so?:

No. Steerer should protrude above the top of the stem by 3mm (ish). This allows the stem loads to be supported on the steerer over its full height. Then add a spacer above the stem for the top cap to clamp down on.

ben----- wrote:

One thing I'm not understanding is tightening the top cap doesn't seem to effect the stiffness of the handlebars turning. I haven't put a lot of force on it but tightening it doesn't result in the handlebars not turning so easily.

Assuming you haven't tightened the stem clamping bolts, you should notice that tightening the top cap makes the fork turn more slowly when lifted of the ground and tipped to the side. There is a sweet spot between a bit too loose where the fork will rattle when you rock it back and forth with the brake full on, and a bit too tight where it affects the steering.

g00se

stanthomas wrote:

ben----- wrote:

One thing I'm not understanding is tightening the top cap doesn't seem to effect the stiffness of the handlebars turning. I haven't put a lot of force on it but tightening it doesn't result in the handlebars not turning so easily.

Assuming you haven't tightened the stem clamping bolts, you should notice that tightening the top cap makes the fork turn more slowly when lifted of the ground and tipped to the side. There is a sweet spot between a bit too loose where the fork will rattle when you rock it back and forth with the brake full on, and a bit too tight where it affects the steering.

Another possibility is that the bung is being seated too high up the steerer so that when the top cap is tightened, the lower part of the cap is tightening down against the bung, rather than having the top lips of the cap tighten down against the stem/top-spacer. If this happens, you can tighten all you want but it won't pre-load the bearings.

This predominantly happens with bungs that sit at the very top of steerers - like the deda one:


If the top cap is quite deep, the underside of it will hit the top of the bung first.

balthazar

ben----- wrote:

> I think you have that wedge upside down.

No, it's definitely the right way round there. I got it off using a metal vice. It was through total ignorance of the system that resulted in me getting it stuck like that in the first place.

It's one of these types: http://www.jarredscycling.com/2013/08/t ... adset.html

A main thing which I didn't realise is (I'm completely new to threadless headsets although I don't think this is a particularly normal/standard one), there are two allen key nuts in one as it were -- down the stem. One 5mm which handles the expander (tightens the two wedges together pushing out the expander) and a 6mm one which is the top cap. And you have to get the expander bit inline with the bottom stem clamp -- that's what the bottom stem clamp clamps round.

One thing I'm not understanding is tightening the top cap doesn't seem to effect the stiffness of the handlebars turning. I haven't put a lot of force on it but tightening it doesn't result in the handlebars not turning so easily.

Anyway, got it all back together now. Hopefully all will be well. Thanks.

Right, the picture in that link makes sense! So the bung is missing in your pic (apart from one wedge). Glad you got it all together.

Nonetheless, I still suspect that the bung is slipping: that clearly happened already, and from what you say, still is. Tightening the top cap applies preload that will lock out the headset quickly and obviously in only an extra turn or so. If it doesn't do this, then it isn't doing its job- something is slipping or binding. It's possible to get the headset preload about right without a properly functioning top cap bolt, but not ideal.

mr_evil

Expanders do need to be done up quite tight (the last one I fitted specified 10Nm).

Bordersroadie

Monty Dog wrote:

IME it's usually down to the bars rotating downwardsslightly in the stem due to the impact - sounds a lot worse that it is.

+1

Another vote for this. Makes a horrible noise. I was convinced it was something serious but a quick tighten of the stem front clamp, problem solved.

ugo.santalucia

Expanders are a bad solution to a problem created by the industry itself. The star nut was already an abomination, but at least it did the job. The only way I managed to get a few miles out of an expander before having to re-tighten everything was to wrap it in folded sandpaper... that way it did enough bite on the carbon to load the bearings without coming loose.

Matthewfalle

Actually - sorry - my bad: looking at that picture on my computer as opposed to the TV with tired eyes you can see that the steerer doesn't cover the stem bolts: it needs to do this so that clamping loads are covered (at the moment its going to squash the top of the steerer and the stem bolts have nothing to clamp onto).

Simple solution to this is to get a stem that has less stem height (ie not the length of it but actually how big it is) - so long as the stem bolts have steerer to grip onto then all is well.

My comments re 5mm or so gap between the top of steerer and headset preload adjuster bolt, either by use of a spacer or just the height of the stem itself remain though.

g00se

ugo.santalucia wrote:

Expanders are a bad solution to a problem created by the industry itself. The star nut was already an abomination, but at least it did the job. The only way I managed to get a few miles out of an expander before having to re-tighten everything was to wrap it in folded sandpaper... that way it did enough bite on the carbon to load the bearings without coming loose.

Some bungs are better than others - the Deda one (and similar) will bite into carbon.

Another solution - especially for carbon steerers that are cut so low that most stems are too big. A bonded sleeve. A metal sleeve - with a star nut already installed - is inserted and epoxy bonded into the steerer - with a bit of the sleeve still showing out of the top. This will prevent the steerer splitting - and also help prevent over-torque crushing. My Kyklos came like this (though i think this was done by the previous owner) and i think Cervelo do this too.

on-yer-bike

That small crack has been caused by the top bolt of the stem crushing the top lip of the steerer. You should have a 5 or 10 mm spacer on top of the stem so that the steerer protrudes slightly above the stem before the spacer and top cap go on. Make sure there is no grease inside the steerer that will prevent the plug from gripping. As mentioned it seems to be an ongoing problem that the plugs start pulling up before the bearings are loaded. I would put super glue around the top of the steerer to stengthen it and you can get plugs that have a lip that rests on top of the steerer wich will give you 2 mm of extra height as well as protect the steeer.

ugo.santalucia

g00se wrote:

Some bungs are better than others - the Deda one (and similar) will bite into carbon.

Another solution - especially for carbon steerers that are cut so low that most stems are too big. A bonded sleeve. A metal sleeve - with a star nut already installed - is inserted and epoxy bonded into the steerer - with a bit of the sleeve still showing out of the top. This will prevent the steerer splitting - and also help prevent over-torque crushing. My Kyklos came like this (though i think this was done by the previous owner) and i think Cervelo do this too.

I have a deda similar, the PRO one, and it's shxxe...
If you have to add a metal extender to a carbon steerer, is it not a better idea to get a metal steerer in the first place and avoid the bodged epoxy work? Sometimes one has to give up on a bad idea, rather than insisting... the hassle is really not worth the 100 grams weight saving of a carbon steerer