Expansion plug on carbon steerer popping up. Any Pro-tip?

serviceguy

Well-Known Member
Every time I ride my full rigid SS with a carbon fork on some rather rough terrain the headset comes loose and the expansion plug pops just slightly out of the steering tube. I tried with carbon paste both on the pug contact surface and the inside of the stem clamp but it keeps happening. There's no damage to the fork or the headset, yet it's rather annoying. Is this just part of the game of riding a full rigid carbon fork or is there any pro-tip that can help fix this issue or at least make it better. I'd like to add that I don't seem to have the same problem with my fat bike where I use the same expansion plug even though it's an alloy steerer.

I'd rather avoid fire because the frame is white and wouldn't look that nice.
 

FrankV

Active Member
I don’t run a rigid fork on my bike, but this sounds like possibly a crack. Maybe someone can back me up on this theory, but the steerer could be cracked on the inside that you don’t know about. This would allow the plug to loosen.
 

Karate Monkey

Well-Known Member
I don’t run a rigid fork on my bike, but this sounds like possibly a crack. Maybe someone can back me up on this theory, but the steerer could be cracked on the inside that you don’t know about. This would allow the plug to loosen.

Maybe, but they typically place the clamping elements in the same area that the stem will be, so that they are supported.

@serviceguy you are using a torque wrench to install the bung, right? They're typically 8-10nm, which is ALOT higher than 99% of people are comfy with doing by hand on a carbon fiber part. What brand is the plug? We have good luck with the FSA style. Also, if your plug/starnut is slipping, your stem probably isn't tight enough, either.
 

Mr.Moto

Well-Known Member
Wouldn’t the plug be just for preloading? It would be the stem that provides the retention.
 

serviceguy

Well-Known Member
Maybe, but they typically place the clamping elements in the same area that the stem will be, so that they are supported.

@serviceguy you are using a torque wrench to install the bung, right? They're typically 8-10nm, which is ALOT higher than 99% of people are comfy with doing by hand on a carbon fiber part. What brand is the plug? We have good luck with the FSA style. Also, if your plug/starnut is slipping, your stem probably isn't tight enough, either.
You got me there...I need to get the torque wrench out and do my homework. But yes, in general I'm very nervous about over torqueing on carbon, both the plug and the stem, so that seems to be the most likely reason.

This is what I use currently.
compression plug.JPG

I'm thinking to get one of this instead for added contact surface...
71ezwhqYdtL._AC_SL1500_.jpg


Wouldn’t the plug be just for preloading? It would be the stem that provides the retention.
The stem is supposed to slide/slip before breaking the steerer or handlebars on impact, when sliding up it seems to push the plug out of the steerer.
 

Magic

Formerly 1sh0t1b33r
Team MTBNJ Halter's
Going off this ^, make sure you have enough spacers under the top cap. You may not notice if it bottoms out on something or not, but you may have play. I've made that mistake a few times. I have carbon paste in my carbon fork expansion plug as well, and a tiny bit on the stem.

The plug/cap really shouldn't matter after initial pre-load and stem install, so as long as the stem is solid, it's weird that the plug would pop out without any load on it.
 

Karate Monkey

Well-Known Member
Not easy to tell from the photo, but if the one you are using is an 'all-in-one' plug that you don't tighten separately from the top cap, pitch it in the garbage and grab a proper one.
 

serviceguy

Well-Known Member
Do you run a 5mm spacer between the stem and top cap?
I do (actually a k-edge garmin mount and 5mm spacer).

Going off this ^, make sure you have enough spacers under the top cap. You may not notice if it bottoms out on something or not, but you may have play. I've made that mistake a few times. I have carbon paste in my carbon fork expansion plug as well, and a tiny bit on the stem.

The plug/cap really shouldn't matter after initial pre-load and stem install, so as long as the stem is solid, it's weird that the plug would pop out without any load on it.
I found out the first time I used one of these plugs:oops:, it's actually obvious as you will not be able to tighten a spacer or a garmin mount like in my case.

Not easy to tell from the photo, but if the one you are using is an 'all-in-one' plug that you don't tighten separately from the top cap, pitch it in the garbage and grab a proper one.
Do they even sell those anywhere? But no, it's a two piece, first the actual plug then the top cap threading inside the threaded shaft that compresses the plug.
 
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