Bicycle Mechanics - Freely-turning headset cap nut bolt

This is a cross-post with the C&V forum, because I'm basically a C&V guy--don't do much with modern bikes.

My wife's hybrid has a small amount of play in the headset. I went to tighten it in what I think is the usual way: loosen the pinch bolts, then tighten the cap bolt enough to get rid of the play. Didn't work: the cap nut turns freely, but is evidently stripped--where it threads into the star nut, I'm guessing. The solution should be to remove the cap bolt and cap, drive the old star nut further into the steerer (not a carbon steerer or frame), and thread in a new cap bolt.
The problem is that the damn cap bolt won't come out. It turns freely, but I can't think of a clean way to get a strong enough grip on it to remove it. I tried all the easy obvious stuff, like pulling up on the (loosened) stem while turning the bolt, gently prying up on the cap with a screwdriver, etc.
This can't be an uncommon problem. Any ideas? Sacrifice the cap bolt by drilling a bunch of holes around the bolt head? A dremel or rotozip-type tool would make that easier, but I don't have one.
As an aside, I'm kind of confused as to how this bolt stripped in the first place. I had it out a year or so ago to install a stem extension so V. could ride the bike after some shoulder surgery; after she healed I took off the extension and reinstalled the stem directly on the steerer, adjusting it correctly at the time--I know I didn't overtighten it. What gives?

The bolt might not be stripped. I've seen cases where the threaded core came loose from the leaves of the star nut, which is a pain.

The easiest way (sometimes) is probably to drill the bolt out. Use the biggest drill you have shy of 6mm, so it doesn't seize in the hex (or go the opposite and used one bigger than 5/16"). If the bolt spins, setting the drill at an angle will stop it. Once you drill below the head of the bolt the head should be free from the shaft of the bolt, if not either use a larger drill, or if the bolt is hanging together by one side, use a punch to hammer it off the head. Depending on how rough you were, you might need a new top cap, but most likely you won't.

Is there any resistance at all when you try and unscrew the top cap bolt? If so and it is the threaded core of the SF nut, you might want to try cutting a 6mm allen wrench (or something similar so it will fit in a drill bit) and use the drill motor to unscrew the bolt. At a high speed you may get the threaded core to start to break up or bind and the bolt will come out.

Is there any resistance at all when you try and unscrew the top cap bolt? If so and it is the threaded core of the SF nut, you might want to try cutting a 6mm allen wrench (or something similar so it will fit in a drill bit) and use the drill motor to unscrew the bolt. At a high speed you may get the threaded core to start to break up or bind and the bolt will come out.

Very resourceful--the idea being to spin the core in the star nut so fast that you get it to heat up and seize in place, letting the cap bolt come out of the core? It might work--there's some resistance to the bolt turning, but not much, so I'm not sure I can generate enough heat to get it to seize. I'll try and report back.
FBinNY, thanks for your suggestion also. I'd thought of trying to drill the cap bolt out, but figured that it would just spin in place--hadn't thought of the idea of going in at a slight angle to prevent that.
One way or the other, this sucker is coming out.
JV

Remember, the starnut, top cap and bolt are cheap so destructive removal isn't a bad idea. Any LBS should have replacements and there are companies that sell decorative and personalized caps and you may even want one of those

Success! Onespeedbiker, your method worked. The most time-consuming part was sawing off the allen wrench--very hard steel, and the only hacksaw blade I had on hand was well-used. Chucked it into the drill and spun the bolt at top speed for about five minutes--got a thread of smoke rising before the bolt suddenly backed out. Both it and the cap were very, very hot, but seem undamaged. Now that the star nut is exposed (and cooled back down) it's easy to see that the core is turning in the body of the star nut. That's not a mode of failure I'd ever considered before.
Thanks for the help. Now to drive down the old SN, install a new one, and I'm back in business.
I still prefer threaded headsets. But I will admit that this was easier than boring out a quill stem that had seized to the steerer.

. The most time-consuming part was sawing off the allen wrench--very hard steel, and the only hacksaw blade I had on hand was well-used.
For future reference, good quality allen wrenches are almost impossible to cut with a hacksaw, even with a new blade. The best way to cut them is with a Dremel and a fiber cut-off wheel.

Success! Onespeedbiker, your method worked.
Even a blind squirrel finds an acorn once and a while; glad it worked out :thumb:

For future reference, good quality allen wrenches are almost impossible to cut with a hacksaw, even with a new blade. The best way to cut them is with a Dremel and a fiber cut-off wheel.

Same as cutting down a drill bit. Try a 'bi-metal' blade. They will buzz through these hard steels. I just put the item in a good vice and use a saws-all (reciprocating saw) with a bi-metal blade... will go through a 6mm in a few seconds. Just be sure to let the cut item cool down before touching it.

Same as cutting down a drill bit. Try a 'bi-metal' blade. They will buzz through these hard steels. I just put the item in a good vice and use a saws-all (reciprocating saw) with a bi-metal blade... will go through a 6mm in a few seconds. Just be sure to let the cut item cool down before touching it.
Right. I keep a dish of cold water next to the vise and dip the allen key in it periodically while using the Dremel and after the cut is complete.

Saves trouble with allen wrench cutting:

281113

Every house should have a set. :)