Headset top cap will not tighten

[EzaBlade]

I have a problem of my own making but I'm hoping to find a way to solve it and any help would be appreciated.

On my Canyon Endurace I decided to service and degrease the headset bearings. I loosened the stem bolts and removed the top cap and spacers. Based on watching some you tube videos I was expecting the fork to be removable, some videos even said to hold the fork in case it actually fell out at this point.

(The fork is carbon)

However, in my case I could not shift it. I looked down into the top of the fork and could see the top of another Allen bolt so I decided to loosen this, assuming it to be the reason the fork would not come out. It appears that the top cap bolt goes through the head of this bolt and tightens into another thread.

This did nothing and I found that the tightness of the top bearing on the fork was preventing the fork from falling out so I carefully tapped this slowly off from the top so that the fork could be removed. All good I think! I proceed to clean and regrease the bearings that were ok (there's not a massive mileage on the bike).

The problem occurred when trying to put everything back. I carefully tapped the bearing back onto the top of the fork. I then tried to tighten the Allen bolt down inside the top of the fork, but it just went round and round without tightening. This wasn't looking good. I thought maybe if I continue and refit the stem and the top cap that it may tighten but of course it didn't. I now have a stem installed with a top cap that won't tighten and something inside the fork that must not be doing its job - and can't get the stem back off.

Any suggestions on what to do fix this would be much appreciated.

 

[bikingdad90]

Is it a fully carbon steerer or a carbon fork with bonded alloy steerer tube?

 

[fossyant]

Have you accidentally undone the wedge in the steerer and it's now turning when you tighten the top cap.

 

[Sharky]

Google this
head set compression wont tighten

May give you an idea of what's happening.

 

[fossyant]

You may have lost part of it

 

[Sea of vapours]

I then tried to tighten the Allen bolt down inside the top of the fork, but it just went round and round without tightening.

This is (almost certainly) the root of the problem. What's inside the steerer tube is a compression bung. It's there solely to allow the top cap to be tightened to take the play out of the headset bearings *before* you then tighten the stem bolts to actually hold everything together.

You need to loosen the stem bolts and remove the top cap. The compression bung then needs to be tightened in place before replacing the top cap and preloading the bearings. The bung will look much like the photo below. Ideally, fish it out of the steerer tube so that you can see how it works, but essentially the allen socket you originally loosened is pulling a cone up from below and expanding the bung to grip the inside of the steerer tube. If it's just spinning, as you say, then it's too loose to get the cone to engage, so the cone is rotating beneath the whole assembly. So, find something to extract the bung (a pick used only on the metal bits, not anywhere near the carbon steerer tube), determine how the bung works, then you can put appropriate tension on it before slotting it back in to the same depth. It needs to be expanded to be a snug fit to ensure that you can then turn the currently loose allen socket and tighten it up. You do *not* need much force on these.

As above, try to find a YouTube video showing how bungs function as that'll be clearer than verbal descriptions! As also stated above, it's conceivable that the cone part has dropped off the bottom of the bung, in which case inverting the steerer will be necessary to retrieve it, once you have the main part of the bung out. If in any doubt at all as to whether you've got this right at the end, find someone to check it !

 

[Big John]

Have you got a fixed star nut in the steerer or an adjustable/removable one?

Edit : just seen the post above which suddenly appeared as I was typing this.

 

[Smokin Joe]

This is (almost certainly) the root of the problem. What's inside the steerer tube is a compression bung. It's there solely to allow the top cap to be tightened to take the play out of the headset bearings *before* you then tighten the stem bolts to actually hold everything together.

You need to loosen the stem bolts and remove the top cap. The compression bung then needs to be tightened in place before replacing the top cap and preloading the bearings. The bung will look much like the photo below. Ideally, fish it out of the steerer tube so that you can see how it works, but essentially the allen socket you originally loosened is pulling a cone up from below and expanding the bung to grip the inside of the steerer tube. If it's just spinning, as you say, then it's too loose to get the cone to engage, so the whole assembly is just rotating. So, find something to extract the bung (a pick used only on the metal bits, not anywhere near the carbon steerer tube), determine how the bung works, then you can put appropriate tension on it before slotting it back in to the same depth. It needs to be a snug fit to ensure that you can then turn the currently loose allen socket and tighten it up. You do *not* need much force on these.

As above, try to find a YouTube video showing how bungs function as that'll be clearer than verbal descriptions! As also stated above, it's conceivable that the cone part has dropped off the bottom of the bung, in which case inverting the steerer will be necessary to retrieve it, once you have the main part of the bung out. If in any doubt at all as to whether you've got this right at the end, find someone to check it !

View attachment 774394

Wot 'e said.

I had the same problem when I first used a bung instead of a star nut.

 

[Dogtrousers]

This is my nightmare.

It's why I always get my LBS to do maintenance on threadless headsets. I've disassembled and reassembled loads of the old fashioned threaded ones, but never these. I can check them for play and adjust if necessary, but that's all.

My advice: gather all the bits together and go to a bike shop you trust. This is precisely what I did last year when I ballsed-up replacing my BB. https://www.cyclechat.net/threads/in-praise-of-my-lbs.298367/

 

[Ajax Bay]

The bung which the OP has loosened (by 'unscrewing the "another allen bolt") has slipped down (my guess).
"I looked down into the top of the fork and could see the top of another Allen bolt so I decided to loosen this,"
Now it's too low for the top cap bolt to engage so
"it just went round and round without tightening."
As @Sea of vapours describes, long bolt (same thread as top cap bolt) to reach down and engage bung and pull back up.
Then position the bung inside the steerer tube where the stem will be clamped and tighten it (allen key) to secure there.
Reassemble, slide on stem but not tighten, on with a spacer and the top cap, and the top cap bolt will engage "the top cap bolt goes through the head of this bolt" and provide light compression.
Secure stem.

 

[fossyant]

See post 3. Canyons have a bung that's tightened by a larger hex key so I suspect OP has undone it and it now turns. The top cap bolt then tightens into the threaded hex bolt on the bung.

https://www.canyon.com/en-pl/gear/b...wear-parts/canyon-e201-15-wedge/10010634.html