Bicycle Mechanics - SID WC Carbon Steerer, can't get that plug to stay.

So I just purchased a 2005 SID World Cup with carbon steerer. I have the top of the steerer EXACTLY flush with the top of my stem and then an additional 10 mm spacer. I thread the cap into the plug (or bung for you overseas-ers), which is supposedly specially made for carbon, and begin tightening the stack. I have tried this several times, and each time the plug, instead of expanding and staying put, moves up and out. I tried to increase the pressure on the steerer, and thus the plug, by tightening the bolts on the stem (slightly) first, but I'm not sure this is allowing adequate pressure on the stack because I can still detect faint movement. Any thoughts, help?

Have you tried expanding the plug outside of the steerer so it just barely fits into the steerer, and sort of mushing it down into the steerer and then tightening? That always works for me.

I will try that next, for sure. Is this a common issue with expander plugs? Also, is the expander plug serving a dual duty by also adding strength to the carbon steerer tube?

I will try that next, for sure. Is this a common issue with expander plugs? Also, is the expander plug serving a dual duty by also adding strength to the carbon steerer tube?

the plug needs to grip the steerer walls a little bit before the plug moves up and expands. if its not touching the walls it will just spin around. as far as adding strength goes it depends on the design of the fork or plug.

Not sure what type of plug you have. Some plugs thread into the top cap. The top cap should have 6MM hole and the plug will have a 5mm hole. Scre the top cap onto the plug and insert into the steerer. then tighten the plug with a 5mm Allen wrench. Remove the top cap and inspect. I had to do this yesterday in the shop.

When I put the cap on, thread the bolt into the plug and start wrenching, I can hear the darn plug inside the steerer sliding up. It has enough friction not to fall out and enough to make a carbon fiber-y noise as I tighten and it slides, but it still slides up. So, I put the plug flush with the top of the carbon steerer, put the stem on, and tightened the stem bolts just slighty enough to grab the plug, and preloaded the headset that-a-way. It seems to have worked for now- no serious audible or physical movement. Still concerned I didn't do this appropriately, however, and I don't want to find out the hard way on the Spruce Creek trail in Blue River.

You need to explain if your plug has a separate center bolt to expand it, or if the top cap bolt serves a dual purpose - to both expand the plug and tighten the top cap. The later just does not work as well. It can take serval tightenings until it finally grabs hold.

If you are using a 10mm spacer on top of the stem, the steering tube should have been cut to extend above the stem by 2-5mm, not cut flush with the top of the stem. That insures that the top spacer is centered and not restricitng the steering tube from moving up an down.

For everybody's information, this is what I did:

I found that a 17mm socket fit perfectly inside my carbon steerer tube and mated directly with the top of the expander plug. I used the same bolt from the top cap, but put it through the hole in the 17mm socket with a washer. When I threaded it into the expander plug and tightened it, it allowed me to effectively pull the inside of the expander up while keeping the outside of the expander in place (since it was the registering surface). SO, I was able to tighten the expander plug in place, right where I wanted it. After it was tight, I backed the top cap bolt out, re-installed it in the top cap and, with the proper spacer, put it back on. I was then able to preload the bearings just fine.
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