Interesting! I assume that at some point Shimano gave up on insisting that teams use threaded Shimano headsets? Why doesn't Shimano just make a threadless version themselves, anyway?

I've thought about doing this mod myself, though it seems like it would be tricky to get it just right without a reaming tool that perfectly fits the steer tube diameter.

Sorry, I wasn't clear. The TOP race is threaded and attaches to the fork, but the race that goes on the frame doesn't thread at all. The spacers would go above the race but below the nut right?

One other thing to consider, if the threads extend too low. You should not install a stem whose clamp extends into the threads.

That makes no sense. You're talking about a quill stem, right? If so, the threads are at the top and any stem will extend into them. Furthermore, on a frame as small as mine, the stem actually goes all the way to the bottom of the fork if you put it in all the way. My stock one would bottom out with about 1/8" to go.

Or did you mean the stem should go PAST the threads? If so, I should be safe. The clamp is like 2-3" down and I put it in most of the way.

I think what ISeeDeadHuffies is referring to is if you put a threadless stem on a threaded fork, the clamp should not go over the threads. Sorry for the confusion I've created by bringing up the decidedly unorthodox idea of converting an extra-large threaded fork to threadless :)

Ahh yes, I was being selfish and only thinking of me me me. Absolutely correct, you'd want to cut the threaded part off to do that. My apologies as well.

Apparently Shimano refused to license the original patents for threadless headsets so they never made any and pretty much have abandoned the headset market.

As to doing it yourself, it would be very difficult to hand ream or free-hand file away the threads while maintaining adequate concentricity. It would require a lathe and good technique to do it properly.

What I was refering to is that the expander wedge on a quill stem needs to be below the threaded section of the fork.

Ahh yes. Actually, it SHOULD be ok as long as it's not against the part of the threads that is threaded in the headset (pushing against the two threads can seize them up). But it's probably a good idea to get it down in there anyway. No worries, I put my stem as deep as it goes right now since it's a 0 degree rise.

Absolutely, it's not an easy thing to do accurately, no question about it.

It's just funny because you can basically make a threadless headset by carefully removing the threads from the adjustable race (even though it's difficult to do right), and throwing out the locknut. Who had the original patent, DiaCompe? I wonder if Shimano will get back into headset once the patent expires (~5-10 years from now I would guess).

Got the fork today, and I need about 2 or 3 more threads. So I'll find a shop that can do that, but my bigger concern is that the fork blades are about 1/2" shorter than the stock fork. The wheel still fits with plenty of clearance, but we'll see how well it clears the shoes or affects the steering.