Top cap and spacers above stem keep coming loose?

[cyan]

Have a CK noThreadset setup with 10mm spacer under stem and another 10mm above it. Tightened the top cap bolt to set the headset bearing first before tightening the stem clamp bolts.

No obvious play in the headset when rocking the frontend of the bike, yet the after the stem bolts are tightened both the top cap and the spacers above the stem become loose, i.e. both rotate but the top cap bolt stays put.

Any idea what may cause this and does it affect function or safety in any way?

[lhuerta]

...the underside of ur top cap is likely bottoming out on your fork steertube. U need to add more spacers or trim ur steertube.

[zmalwo]

once the stem bolts are tight the top cap loses its function. You can even take it completely off to save some weight. more than likely your spacer above the stem is too short and the cap is hitting the steerer.

[cyan]

once the stem bolts are tight the top cap loses its function. You can even take it completely off to save some weight. more than likely your spacer above the stem is too short and the cap is hitting the steerer.

...the underside of ur top cap is likely bottoming out on your fork steertube. U need to add more spacers or trim ur steertube.

Thanks for the pointer. I always thought if there was not enough space below the top cap then there is limited adjustment of headset bearings with the top cap bolt. In my case, before tightening the stem bolts, I can further tighten the top cap bolt to reduce the gap between the bearing cap and the upper bearing cup thus pressing harder on the bearings. Doesn't this mean there is enough (and more) space under the top cap and it is not bottoming out here?

Please correct me if I get it wrong.

[ultraman6970]

Put a larger spacer and I would look at the expander aswell, it might be getting lose. Do you have a larger expander?? IME Depending on the fork sometimes you have to go with a longer expander because the regular short ones tend to move. It happened to me twice.

[Dave]

A slipping expanding plug is likely. I quit using expanding plugs many years ago. Instead, I epoxy glue a 1 inch star nut, that's had the tips of the stars filed down a little so it slides into the steering tube. I've also used 6mm tee nuts, but those are tricky to align.

The result is a permanent, crush proof area that requires no spacer on top of the stem.

My bikes have no spacer under the stem either, so any height increase would be done with a stem angle change.

[Mark McM]

A slipping expanding plug is likely.

This is my bet as well. The expander might hold well enough when adjusting the headset bearings, but over time it could slip under the shock and vibrations of riding, loosening the preload on the top cap bolt. Try a different expander, one that grips the inside the steerer better.

[weaponsgrade]

I’ve had this happen as well. What worked for me was switching to Park carbon paste. I think the park carbon paste had bigger particles which helped keep the stem secure to the steerer. I’ve heard specialized makes a very good expander plug.

[kramnnim]

A slipping expanding plug is likely. I quit using expanding plugs many years ago. Instead, I epoxy glue a 1 inch star nut, that's had the tips of the stars filed down a little so it slides into the steering tube. I've also used 6mm tee nuts, but those are tricky to align.

The result is a permanent, crush proof area that requires no spacer on top of the stem.

My bikes have no spacer under the stem either, so any height increase would be done with a stem angle change.

When you have a few minutes, could you take a photo of this?

Wondering if the clamping force of the stem would be putting pressure on the blob of epoxy, or on the star nut (which may dig in to the carbon?)

[Dave]

When you have a few minutes, could you take a photo of this?

Wondering if the clamping force of the stem would be putting pressure on the blob of epoxy, or on the star nut (which may dig in to the carbon?)

If a star nut is epoxied in place, a foam rubber plug must be placed below it to keep the epoxy from running down the steering tube and the star nut placed low enough. It could be placed low enough to allow the top 10mm of the steerer to be cut off at some point. The epoxy fill level should be stopped 2-3mm below the top of the steering tube, to avoid contact with the top cap. Some caps have a recessed bolt that may require using a large countersink tool or a dremel tool to add clearance at the center, around the top cap bolt.

Of course the stem puts pressure on the steerer and the epoxy, but JB Weld epoxy has a tensile strength of 5000 psi. The star nut can't damage the steering tube, when it's totally encapsulated in epoxy.

I have more detailed instructions that I can send.

Here's a link to a drawing that someone made. See post #21.

https://www.bikeforums.net/bicycle-mechanics/1193593-compression-plug-oval-carbon-steerer.html

This picture shows that last steerer that I did, where I used a 6mm tee nut that's used to put metal threads into wood. The center of the epoxy has been countersunk for some additional clearance.

https://forums.thepaceline.net/picture.php?albumid=93&pictureid=575

[cyan]

This is my bet as well. The expander might hold well enough when adjusting the headset bearings, but over time it could slip under the shock and vibrations of riding, loosening the preload on the top cap bolt. Try a different expander, one that grips the inside the steerer better.

A slipping expanding plug is likely.

Put a larger spacer and I would look at the expander aswell, it might be getting lose. Do you have a larger expander?? IME Depending on the fork sometimes you have to go with a longer expander because the regular short ones tend to move. It happened to me twice.

The fork is an Enve and I'm using its original expander, which has larger top that rests on the top edge of the steerer when inserted. Even when it's not expanded, it just sits there so am not sure how it could "slip". Admittedly, it's not as long as the stack height of the stem. I torque the expander to 7nm which is what is specified on Enve's fork installation page but in its instructions video they say 8nm..

[kramnnim]

If a star nut is epoxied in place, a foam rubber plug must be placed below it to keep the epoxy from running down the steering tube and the star nut placed low enough. It could be placed low enough to allow the top 10mm of the steerer to be cut off at some point. The epoxy fill level should be stopped 2-3mm below the top of the steering tube, to avoid contact with the top cap. Some caps have a recessed bolt that may require using a large countersink tool or a dremel tool to add clearance at the center, around the top cap bolt.

Of course the stem puts pressure on the steerer and the epoxy, but JB Weld epoxy has a tensile strength of 5000 psi. The star nut can't damage the steering tube, when it's totally encapsulated in epoxy.

I have more detailed instructions that I can send.

Here's a link to a drawing that someone made. See post #21.

https://www.bikeforums.net/bicycle-mechanics/1193593-compression-plug-oval-carbon-steerer.html



This picture shows that last steerer that I did, where I used a 6mm tee nut that's used to put metal threads into wood. The center of the epoxy has been countersunk for some additional clearance.

https://forums.thepaceline.net/picture.php?albumid=93&pictureid=575

Thanks! I wasn't sure how much epoxy was used, this makes sense. (I was thinking that if only a minimal amount of epoxy was used, the star nut itself would be taking the clamp pressure, and that might not be ideal.)