Currently feel like the worst mechanic in the room. I am at war with my compression plug.
Backstory: I was adjusting my handlebars, stem, cleaning fork etc. and now I can’t get my compression plug back and fitted as it came out when I unscrewed my top cap.
So I have everything in order, exactly as it was pre bike cleaning. My spacers are in the order as before and stem is at the same angle. I can’t get my compression plug to stay in the fork and tight. I can get my plug to the point where I feel resistance when screwing the top screw and topcap in, but I am able to rotate the top caps freely and even pull the compression plug with top caps out of the fork as 1 unit. My stem screws are not tightened on either side. I have a carbon fork.
I’m guessing the threaded cone isn’t engaging with the expansion sleeve/wedges (depending on the design), and is just spinning when you turn the bolt.
Lift up on the cap when starting to turn the bolt so that the cone doesn’t spin (it’s pressed up against the sleeve), it starts moving up the bolt and expanding the sleeve/wedges.
Take it out and turn the bolt to expand it a bit more so that it can grab the steerer tube a bit more. Then put it back and try to expand it more to grab properly.
yes, as Jim said… The key is to get the plug pre-expanded as much as possible before inserting into the steerer tube. You want to press the expander plug back into the steerer tube with a slight bit of resistance, witht he stem bolt and top cap and ring spacers already in connected order. You may even have to lightly tap the whole assembly down into the steerer tube. This is fine, as it means the plug is pre-expanded and when you begin to tighten the cap bolt, the plug will lock into place against the walls of the steerer tube.
Also, de-grease (ie: brake parts cleaner) the inside of the steerer tube and the outside surface of the plug itself. This will help to ensure the plug grips the steerer tube walls.
Ok, back at it today and things are improving but still need some advice.
I have a KCNC expander plug (https://fairwheelbikes.com/kcnc-expander-plug/). I am able to tighten the hex on the bottom of the compression plug enough that there is resistance when I put it in the fork. I’m now confident that I’m good through this step.
My issue is when I go to place the top cap on and screw the top bolt in. I screw the top-cap bolt in and it essentially disengages the expander plug. I can pull out the expander plug with the spacers and top cap still attached with the top-cap bolt.
As you pointed out, tightening the top cap (into the ID of the screw that tightens the expander) can cause the expander wedge to loosen. One thought is to use teflon tape (plumber’s tape: $0.99 for a roll at any hardware store) on the expander screw to increase the friction with the “lower” top cap (the one with the remove and install arrows). That way it’s less likely to rotate when you screw in the top cap.