you could try aluminum foil to wedge the Allen bit in. The impact might get it out with zero damage.

Right; apologies all'round for my misread.

Yep, those pics show that clearly.

Too, it's possible that there's so much rust around and under the head of that sunken Allen head you're not getting much (if any?) penetrant down where the threads that need it live.

Also possible that whomever installed that stem didn't use a split lock washer underneath the bolt head, why it might have been overtightened & why also what's left of space under bolt head & stem bore is rust filled.

Barry2's suggestion of using a Torx tip is a good one, if you have one that'll fit tight into that buggered hex bore.

Torx 40 measures 5.76mm across pairs of tips, 6.47mm across opposite points. Allen 6mm measures 6.72mm across opposite points; 7mm Allen measures 7.89mm across opposite points.

Making sure your Allen tip is square and 'sharpish' at the end is a really good idea! This isn't something to attempt with a ball-end wrench.

(Take a moment (if you would) to wick out the penetrant in that buggered Allen bore, take another pic of it dry, post it here. I'm curious what shape it's presently in.)

A 7mm Allen tip, slightly 'modified' with a stone on a bench grinder or Dremel may be the ticket. You want whatever tip you deploy to bottom out in the bolt head's socket, and if the fit is tight enough (why the modifying) to bite into what's left of the corners it ought to come free with an impact tool.

Leaving your hands free to apply forward pressure while the impact does the twisting's the key here. This isn't something you want to try using a simple L-shaped Allen wrench alone.

Yeah I feel your pain there. That's a beauty you've acquired!

Once you've succeeded in getting that stem free, do a thorough inspection of the steerer tube inside and out please.

The bolt looks rusted stuck to me. I would be soaking the fluid down the outside now, where the HS nut is. Wrap some gorilla tape around the nuts to make a well. That stem looks pretty long anyway.

Left one boat anchor, right one light and no problem when used properly.

Access to lube/Kroil the bolt threads by loosening the headset top nut?

Hmmm. Worth a try.

I was thinking the same thing. Maybe run a sander on it, minus sand paper, and vibrate the solvent down. The wedge is probably corroded into the stem and steerer.

The manufacturer calls it a hammer:

03-208 Size A Copper/Hide Hammer https://www.thorhammer.com/product/03-208/

I’m sure you probably have plenty of solvent soaked in, that’s good. Another hack that one can try, (dry up the solvent on the bolt head and) epoxy the allen into the bolt.

After this many days and not getting any result. Just drill the head off the bolt. The take hammer or mallet and a punch just a little smaller than the bolt shaft to knock the wedge loose. Then you should be able to remove the stem with no damage, other than the bolt, and replace the bolt. Assuming the hole in the stem cleans up well and the bolt isn't rusted in the wedge also.

I wonder about that stem. I had a TTT stem on my Raleigh Professional that required a 7 mm hex key. The OP states that the 6 mm key they have is a loose fit. Is it possible that this stem also needs a 7 mm hex key?

Have you ever tried a 6 in a 7 bolt?

I tried 7mm and 1/4” which were too big. I tried a 7/32” which was too small. A 6mm allen wrench fits, but there is quite a bit of play. The draw bolt aperture was slightly buggered when I bought the bike from the original owner.

I did purchase a set of these bits which are made to facilitate removal of recalcitrant hex bolts. Fits nicely. I will give it a try with a manual impact wrench once I get a 3/8 to 1/4 adaptor.

Ooooh.
That looks serious!

I have this nos 3TTT stem coming in from ebay assuming the worst for the existing stem. Look at that clean shiny draw bolt head! And special cap to keep the gunk out!!

Given the hidden bolt design, you may be able to replace the buggered one with something from the hardware store.

Nothing has worked. This one is a real bugger. So I drilled out the draw bolt head, let it sit with penetrating oil down at the wedge nut for 48h and hit the top of the bolt with an appropriately sized pin punch and small sledge hammer a whole bunch of times. No dice. Will try the same again tomorrow. (I have a nice nos 3TTT quill stem to use once the old one is out)

I know it sounds a little counter-intuitive, but try placing a block of soft wood on top of that frozen stem then hitting that with the small sledge.

Idea being you may be able to free up the wedge nut by driving it ever so slightly deeper with the stem 'stead of relying on what's left of the draw bolt to stay rigid enough not to bend a little when struck rather than imparting the full force of your hammer to the wedge.

On my original MBGR's stem that draw bolt was about 6" long. When I started 'restoring' it back in '23 its wedge nut'd been 'frozen' for maybe 20 years or more. The draw bolt was fairly easily removed after I'd done the penetrant soak, but stem and wedge failed repeated attempts to remove by twisting the stem... why I'd abandoned further attempts way back then.

One caveat if you're willing to attempt this move: my MB's fork's steel, I didn't want to take a chance of doing it harm by leaving the front wheel mounted. So I pulled the wheel, fashioned a solid support to rest the fork part on where steering tube's mounted before giving frozen stem a couple of whacks with my three pounder. That steerer's not plugged so I could drive the wedge nut out from the bottom; here's what it looked like after all those years inside:

Gotta ask, what penetrating oil are you using? If it's not PB Blaster or Kroil Oil or something similar you're missing out, much more effective. Sorry if this has been answered already but I did a quick look through the posts and I didn't see it mentioned.

so the head of the bolt is gone? In that case take a hack saw and cut off the top of the stem. Now the bolt will stick out well above what’s left of the stem and it’s a lot easier to hammer down on the bolt. If that still doesn’t work then you take the fork off and soak the steerer upside down in a bucket of lye solution until the aluminum stem dissolves.

I was a chemist in my professional life so the idea of dissolving the aluminum in concentrated sodium hydroxide solution was very appealing to me, lol! Fortunately, I did not have to resort to that. Unfortunately, though, I did have to hack saw off the stem so I could better access the wedge nut. I used an appropriately sized steel tube which fit inside the stem and around the drawbolt shaft. With the steel tube in place, the bottom of which was sitting directly on top of the wedge nut, a few surprisingly hefty whacks with a 4 lb sledge hammer were required to free the wedge (the fork was removed from the frame and the dropouts were sitting on a thick board). Then vice grips to grab the stem stub and I was able to get everything out of the steerer. Whew. Seriously, I NEVER EVER expected this much fuss to remove the stem from a 25 yr old bike!! For reference, when I completely overhauled my 1975 Motobecane Grand Record a year ago, I did not encounter anything like this!! Which makes me think…..should I even attempt to adjust the height of the seat on this ‘new’ bike???

Yikes

Yes, for sure an annual loosening and inspection. I bought this bike about a month ago from the original owner who purchased it around 1999. So possibly the stem bolt has never been loosened since then. I live about 1/4 mile from a bay that connects to the Gulf of Mexico, so a ‘salt air’ environment and will be taking extra care of my bikes because of that.

The stem bolt in the picture I posted looks extra groty because it had been soaking in penetrating oil for days and then got covered with metal shavings as I was drilling out the head bolt and then hacksawing off the stem.

I'm glad you took action and did something. However don't you think that drilling the head off of the bolt and then using a punch or something to hammer on the bolt shaft might have loosened the wedge and saved the stem to be used again?

Or where the threads already stripped in the wedge and the shaft moving in it?

Oh well, just make sure to get it sent to a scrap yard or somewhere it will be recycled. If you just trash it, it'll be in a landfill for the foreseeable centuries.

He did that, it didn't work - see post #42