Is this threadless headset using an expansion plug? How do I get the stem off?
I loosened and loosened the bolt on the adjusting cap on this threadless stem as far as it would go, expecting the bolt to eventually come out and reveal a star fangled nut underneath, but it just stayed there, and a cone fell out of the bottom of the headtube. The bolt spins completely freely, but the adjusting cap doesn't want to come out. Here is a photo of my stem:
You can see the space under the blue adjusting cap -- when I look in there, I can see there's a spring under the cap (when I push the cap or the bolt down, I feel the spring resist), and in the foreground, you can see the cone that fell out of the bottom. I'm assuming that what I've got here is an expansion plug system. I think it's the LOOK-style expander plug mentioned in this thread: http://www.bikeforums.net/showthread...-expander-bolt
Note that they point out the visible spring, which I've definitely got. The Park instructions only talk about the two-bolt, springless type:
With the two-bolt type, the top cap should come off, revealing a hollow bolt underneath which I need to loosen. I think I understand that the LOOK style has only one bolt which goes through the adjusting cap, top cone, and bottom cone.
How do I get this stem off? Is it loosened all the way now, and I just need to use lube and strength to get it off? If so, where do I pry? I've tried prying directly underneath the blue top cap, with the stem bolts loosened, but the top cap didn't seem to budge, and I didn't want to force it too much. If this was a threaded stem, I'd flip the bike upside down and spray a ton of solvent into the headtube, then pull and twist on the stem like crazy. I could try that here, but am I prying in the right place? Should I shove a wooden dowel in the bottom of the headtube and tap it?
FYI, this is on a KHS Montana Descent with Rock Shox Mag 21 fork. The SN dates the frame to January, 1996, but the Deore XT RD and Alivio rapidfire brifters date to '99-'02.
I've only ever worked with star-fangled nut threadless and traditional threaded, so this is a new one for me. Any help or insight into this thing is greatly appreciated!
Last edited by pocky; 07-28-11 at 01:42 PM.
Sounds like you have somthing 'like' a FSA Connex expansion bolt, which probably is now stuck with it's own suction. Thinking that all you will probably need is to lever the top cap up, but this may be damaged in the process; the dowl idea is good too.
When you get it out, would go back to the Star nut, as apart from carbon steerers, these are more reliable then expander bolts, I used a Connex BITD with a Mag 21 Sl Ti, and it was soon replaced with a Star nut.
Thanks for the advice, Jim. Are people really expected to have to remove the entire expansion plug on these things just to swap a stem? I suppose if prying the crap out of the top cap damages it, I don't care too much because I'll presumably want to replace it with a star nut anyway, like you said. I'll douse it in penetrating oil and/or WD-40 and/or boiling water to hopefully make the prying/tapping easier.
The Expansion plug 'should' just slide out when the pressure is release from it, in your case, it appears to have stuck / is corroded in place. The problem I had with them BITD was they always loosend up really quick, just the opposite of the issue you are having.
OK, so I pried some more and managed to get the adjustment cap off, but not in the way we both expected:
The hex-shaped stretch in the sheet metal is from the hex nut that was on the top cap bolt, stuck there but turning freely under that hole when I was trying to just unscrew the bolt. By prying, I stretched the hole to accommodate the hex bolt coming out the top.
I tried tapping the plug out, but it was still stuck. Rather than trying more, I figured that now that I can swap stems, I don't really care to get the plug out and replace it with a star nut, though, so this is just fine.
I don't believe the hole being small enough to *not* allow the bolt to come out with the hex nut serves any real mechanical purpose -- it was just small to make sure everything (including the cone at the bottom of the plug) stays together when you loosen everything enough to pull the (non-seized) expansion plug out. I don't really believe the hex bolt serves any mechanical purpose either -- it too is just there to keep the assembly together when you pull the whole plug out.
By making the hole big enough to take the bolt out all the way and fully release the adjustment cap, I've done exactly what I wanted: created an easy way to swap stems. The only inconvenience is getting the bottom cone back in through the bottom of the steerer. For that, I stuck a sticky-side-out ball of duct tape at the top of a metal rod, lubed up the top of the cone, and stuck the sticky rod end on the bottom of the cone:
I put the new stem on and lined the cone up against the bottom of the plug while turning the bolt to get it threaded into the cone. Now I don't really have to ever get the plug assembly unstuck -- I can leave it in there stuck in there permanently and unthread the whole bolt to swap stems as long as I remember to use this trick to replace the bottom cone.
Anyone see any reason why this would ever be an issue? I could presumably even remove the hex nut altogether.
But for now, I put all the parts back in just as before -- I stuffed the bolt and nut back in the hole and folded down the thin metal edges of the hole again to make everything reasonably smooth before tightening down the cap to get the headset adjusted well again.