Hi all. I've noticed my headset knocking a bit under hard front braking and have attempted to loosen the stem cap to check bearings and noticed that the cap bolt has been rounded out by the wrench monkey who put this thing together 15 years ago. What can I do with this to get the head apart?

Screw extractor, then get a new bolt.

Might could find a torx bit that doesn't quite fit and hammer it down in there. Might ruin your torx bit, but those are cheap now. Screw extractor is best bet.

I've gotten things like that out by making a small punch or chisel like tool with sharp edges from tool steel and tapping near the circumference in the loosening direction. Surprisingly worked better than I imagined for being so small.

+1 on Torx bit.

Bin there, got the t-shirt!

Barry

That bolt looks like it's been really wrenched on. Loosen your stem first in case the cap has been wrenched on against the stem.

Thanks for the advice guys. I'll see what I can do with it. I've got a bunch of Torx bits about, otherwise I'll get an extractor.

Easy outs Get a drilled pilot hole, there is a left hand fluted one

To Dig in , as you turn it in the unscrewing direction ..

Wow, that's a lot of damage for a bolt that is only meant to preload the headset.

I’m wary of screw extractors. They’re quite brittle and if they snap before the screw comes out your trouble has immediately multiplied.
I’ve never snapped a Torx yet.
Case like this, I’d be about evenly tempted by trying a Torx or simply reaching for a drill.
Good thing about Allen screws is that they are by nature self-centering when you go to drill the head off. And the steel for a top cap bolt is relatively easy to drill. Run a 5mm drill down there and the head of the screw will come off. That should pop the top cap off, which should allow you to reach in there with a set of pliers and unscrew the rest.

Yeah, I added to it a little when trying various bits to get it out but it was already pretty much rounded out and knackered.

Good idea! Remove as much preload as possible.

the drill out if say 5/16" the cap screw head would fall off, the stem cap coming off ,
Then, you remove the stem, and extract the rest of the bolt with vice grips..

I'd drill it out with a left-hand bit.

How about using a Dremel cutting wheel to cut a slot in it? You are going to toss the bolt so who cares if you disfigure it a bit. Smiles, MH

That sounds like a plan. I could use a coin to loosen and tighten it in future. Weight saving too. :-)

slot that sucker-save your time for riding.