I posted a thread on this site a while back asking why you couldn't use a carbon steerer bung instead of a star nut with an aluminium steerer tube. Some guys said it could be done successfully and they were indeed riding bikes with that type of set up, but it was a complete failure for me. My headset kept on coming loose – don't ask me why – and all I can assume is that it had something to do with the bung. In desperation I ditched the bung, installed a star nut and had a new set up in 10 minutes. What did I learn? That star nuts are specified by all fork manufacturers for use with aluminium steerer tubes because they work. At least I know now.
Carbon bung with aluminium steerer does not work
gizzard
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I posted a thread on this site a while back asking why you couldn't use a carbon steerer bung instead of a star nut with an aluminium steerer tube. Some guys said it could be done successfully and they were indeed riding bikes with that type of set up, but it was a complete failure for me. My headset kept on coming loose – don't ask me why – and all I can assume is that it had something to do with the bung. In desperation I ditched the bung, installed a star nut and had a new set up in 10 minutes. What did I learn? That star nuts are specified by all fork manufacturers for use with aluminium steerer tubes because they work. At least I know now.
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Confusing
Your headset goes out of adjustment when your stem moves on the steerer tube. Once the stem bolts are tightened, you could remove the bung and the top cap and the headset should remain in adjustment. Of course, the bung offers some internal reinforcement to the steerer tube, but since your tube is aluminum, that's not an issue. It sounds like you are using the tension on the top cap to keep the head set in adjustment rather than properly tightening the stem clamp bolts.gizzard said:
It worked for me
I also wonder what you might have done wrong. I have used a top cap with an expnder in aluminum and titanium steerers and have had no problem. Like Kerry says, once the stem bolts are tightened, the only function of the top cap is to fill the hole in the top of the steerers (some total weight weenies remove the top cap entirely).
I also wonder what you might have done wrong. I have used a top cap with an expnder in aluminum and titanium steerers and have had no problem. Like Kerry says, once the stem bolts are tightened, the only function of the top cap is to fill the hole in the top of the steerers (some total weight weenies remove the top cap entirely).
Hi Kerry
Yes, I know the theory and I know for a fact that my stem was not moving on my steerer tube. All I can say is that my headset worked itself loose and I still can't explain why this was. My stem had not moved and yet my forks were moving inside my head tube. Suffice to say that it did not inspire a lot of confidence iwhen I was forced to brake hard.
Now that I have installed the star nut the whole assembly is a lot more snug.
Yes, I know the theory and I know for a fact that my stem was not moving on my steerer tube. All I can say is that my headset worked itself loose and I still can't explain why this was. My stem had not moved and yet my forks were moving inside my head tube. Suffice to say that it did not inspire a lot of confidence iwhen I was forced to brake hard.
Now that I have installed the star nut the whole assembly is a lot more snug.
I understand the function of the top cap (or the lack of function of the top cap in this case) and I would have been happy to remove it and ride the bike because it sure as hell wasn't holding my forks in place. The fact of the matter is that my headset/forks worked themselves loose without my stem moving. I have no idea how it happens (happened)…it just does (did). Now that I have changed to a star nut this seems to have stopped. If someone could provide me with an empirically inspired answer then I'd be happy to listen.
My guess is this: maybe the bung you are using can only expand to a certain diameter which is smaller than the i.d. of your steerer (which might have thinner walls than those found on a carbon steerer)? Then, when you try to put load on the bearings before tightening the stem, the bung isn't doing a very good job.
I have a fork with a threadless steel steerer (with fairly thin walls compared to carbon ones) and was pondering this...
I have a fork with a threadless steel steerer (with fairly thin walls compared to carbon ones) and was pondering this...
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9,419 Posts
You're just rejecting the only "empirically inspired" answers that have been offered.gizzard said:
1. Maybe you're not tightening the stem bolts properly and relying too much on the top cap to keep things from moving.
2. Maybe the bung doesn't fit your steerer well enough to allow you to get the headset tension/compression right. Aluminum steerers often have a larger ID than carbon ones, for which your bung was designed. For my money, this is what happened--and your headset wasn't "working" loose--it was never tightened properly because the bung slipped before you clamped down the stem.
You've denied that number 1 could be happening, in spite of the fact that you can't explain how your headset could possibly loosen without your stem slipping. You've completely ignored the possibility of number 2.
What the heck else do you want, man? Those of use who have have used expander plugs successfully in AL steerer tubes (we're not making it up, you know) aren't just gonna quit because it didn't work for you.
Hey BB
I'm not disputing claims by some people that they have successfully mated carbon-type bungs with aluminium steerer tubes. If you have done it, and done it successfully, then good for you. I wouldn't expect you to stop doing what makes you happy on the hearsay of someone in cyberspace. I couldn't get it right after many attempts and to be perfectly honest I suspect that the bung was somewhat substandard and couldn't expand sufficiently inside the steerer tube to make the whole assembly nice and snug. I know that on all my other bikes (6) which have full carbon forks the bungs are of a much higher quality.
But that still doesn't explain why my forks worked themselves loose after less than 100 miles. The bung is only responsible for providing internal support for the steerer tube and initial downward pressure for the stem before the stem has been tightened fully. Once the stem is in place you should theoretically be able to dispense with the bung/top cap altogether without compromising rider safety. But that still doesn’t get me any close to figuring out why my whole head tube/headset/fork assembly went loose after such a short space of time.
I'm not disputing claims by some people that they have successfully mated carbon-type bungs with aluminium steerer tubes. If you have done it, and done it successfully, then good for you. I wouldn't expect you to stop doing what makes you happy on the hearsay of someone in cyberspace. I couldn't get it right after many attempts and to be perfectly honest I suspect that the bung was somewhat substandard and couldn't expand sufficiently inside the steerer tube to make the whole assembly nice and snug. I know that on all my other bikes (6) which have full carbon forks the bungs are of a much higher quality.
But that still doesn't explain why my forks worked themselves loose after less than 100 miles. The bung is only responsible for providing internal support for the steerer tube and initial downward pressure for the stem before the stem has been tightened fully. Once the stem is in place you should theoretically be able to dispense with the bung/top cap altogether without compromising rider safety. But that still doesn’t get me any close to figuring out why my whole head tube/headset/fork assembly went loose after such a short space of time.
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I'm not certain why you seem to blame the bung for this issue. If I'm reading you right, you say the stem hadn't moved, but the headset had become loose. If the stem hadn't moved, the bung also could not have moved, so whether it was slipping or welded into place makes no difference. Similarly, since a star nut has no locking facility on it's threads, it can't be trusted to hold adjustment any better, even if the anchor end is more solid.
A couple of thoughts arise. You might have gone out of adjustment because your cups or crown race weren't seated perfectly. The difference between too loose and too tight is thousandths of an inch, so even a careful visual inspection might have missed it. Or if your headtube faces weren't exactly parallel, the races could have started tight, but seated more over the first few miles. A loose-ball headset could have been brinnelled in an impact, a cartridge set may have a bad bearing that found some slack. I wouldn't expect it to happen every 100 miles, or to already worn-in gear, but if this was any part of a new installation (other than the bung) it would almost be expected to need an adjustment (and possibly several) within 100 miles.
You seem to say that it slipped when you had adjusted it with the bung, but stayed in adjustment once you've installed the star nut and readjusted. That's probably true. The error is your conclusion is that it would not have stayed in that same adjustment had you used the bung for the readjustment. It might be (and is, if your descriptions are accurate) simply a coincidence that you finally got the rest of the parts seated at the same time that you installed a star nut.
As for the bung being hard to work with in making an adjustment, that's not too surprising. It was designed for carbon tubes, which have both a smaller internal diameter and a less-slippery internal surface than your aluminum steerer. They are typically made to suit the specific diameter of a manufacturer's tubing, so if yours had been designed with a particularly beefy tube in mind, slipping would be nearly guaranteed. All the more so if you didn't scrupulously remove the lubricant that would have been present in the manufacture of the steerer.
I'm NOT starting a "you don't know what you're doing" thing here, because I don't have any way to gauge your experience or see your work habits. But adjusting headsets well does take some experience and some patience. If this is newish territory for you, it might simply be that you had been making the adjustment a bit too loose with the bung, but close enough that you didn't notice it until you were riding. A "slippery" bung would have made proper adjustment nearly impossible.
I have long since stopped using either to make the adjustment. The threads on the cap screw are too coarse (in my opinion) to effect an accurate adjustment easily. A good hard lean on the stem cap with the screw out can be used to make the adjustment with a little bit of practice. (There's an article on Sheldon Brown's about exactly how, if you're interested.) I then re-install the cap and screw, as a bit of insurance.
A couple of thoughts arise. You might have gone out of adjustment because your cups or crown race weren't seated perfectly. The difference between too loose and too tight is thousandths of an inch, so even a careful visual inspection might have missed it. Or if your headtube faces weren't exactly parallel, the races could have started tight, but seated more over the first few miles. A loose-ball headset could have been brinnelled in an impact, a cartridge set may have a bad bearing that found some slack. I wouldn't expect it to happen every 100 miles, or to already worn-in gear, but if this was any part of a new installation (other than the bung) it would almost be expected to need an adjustment (and possibly several) within 100 miles.
You seem to say that it slipped when you had adjusted it with the bung, but stayed in adjustment once you've installed the star nut and readjusted. That's probably true. The error is your conclusion is that it would not have stayed in that same adjustment had you used the bung for the readjustment. It might be (and is, if your descriptions are accurate) simply a coincidence that you finally got the rest of the parts seated at the same time that you installed a star nut.
As for the bung being hard to work with in making an adjustment, that's not too surprising. It was designed for carbon tubes, which have both a smaller internal diameter and a less-slippery internal surface than your aluminum steerer. They are typically made to suit the specific diameter of a manufacturer's tubing, so if yours had been designed with a particularly beefy tube in mind, slipping would be nearly guaranteed. All the more so if you didn't scrupulously remove the lubricant that would have been present in the manufacture of the steerer.
I'm NOT starting a "you don't know what you're doing" thing here, because I don't have any way to gauge your experience or see your work habits. But adjusting headsets well does take some experience and some patience. If this is newish territory for you, it might simply be that you had been making the adjustment a bit too loose with the bung, but close enough that you didn't notice it until you were riding. A "slippery" bung would have made proper adjustment nearly impossible.
I have long since stopped using either to make the adjustment. The threads on the cap screw are too coarse (in my opinion) to effect an accurate adjustment easily. A good hard lean on the stem cap with the screw out can be used to make the adjustment with a little bit of practice. (There's an article on Sheldon Brown's about exactly how, if you're interested.) I then re-install the cap and screw, as a bit of insurance.
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