As previously reported, I'm helping a friend rebuild her International, her childhood bike.

The upper race was very difficult to remove. After I got it off, I saw why, but it's a bit mysterious. There's about 1/4 inch of good threads, then 1/4 inch of what looks like the result of cross-threading or forcing something with the wrong pitch (could that be the case with the headset that was on there?--the race and locknut are both marked 24 tpi).

When I got the race off, I did check the threads inside and there did not seem to be any shavings from either part.

I'm worried about re-installing the headset. This bike only has one fork, and I'm afraid of stripping off the remaining threads so that the headset won't hold together.

Would you chase the threads with a die (and what's the pitch?), or might that just remove precious material which was at least functional that last time the headset was on there?

Id bring it to a bike shop. They can run thier tool down it.It might work when they are done. Dont put anything on it till you chase those threads!

I suspect that someone over (nut) tightened and stripped that particular section of threaded tube.

I'd have the threads die chased, wire brushed clean of any debris, then add (or machine a collar if necessary) a taller washer / spacer to extend the nut grip area onto the upper (good) thread section along with new nuts. You'll be good to go!

Another option MAY be to use a thinner washer / spacer (if clearance and type of current assembly components permit) to allow the nut to ride LOWER on the good threaded section.

There are a couple of ways to correct, or at the very least, salvage the damaged threads.

The best is to see the bike shop and have them chase the threads with the proper die. Make sure the shop is aware of the vintage nature and value of the fork. Or...

You can clean the threads up, individually, with a very small three corner file. This will take an hour, or so, of carefully cleaning/smoothing/forming each damaged thread portion up. Every so often, try your headset nut to see if the threads are improving. Or...

You can take an old, unwanted headset nut, or lock nut, and use it to make your own thread chaser. Cut a single groove, at an angle, into the thread of the lock nut. Just slot to bottom of the thread. This nut, with its slots, can be slowly and carefully threaded onto the damaged steering tube. By going slowly, the slotted nut will actually help to restore the thread.

All three of the above suggestions are not repairs. The threads are not being fixed. They are just being made useable but be forewarned - the threads might not hold well, depending on how much material was originally damaged/lost.

Finally, suggest to the owner to stop mounting their steering stem so high in the steering tube. My guess is that the stem wedge expanded at the threaded section, swelling the diameter slightly in the area that is damaged. Just a guess.

Hope that is a help and I have done this sort of thing many times.

I don't think chasing is going to make that useable -- the threads are pretty much gone. This type of damage usually results from riding the bike with loose headset adjustment. This allows the threaded cup to rock on the steer tube and eventually erode away the threads to the point where they no longer can hold the cup. That's why chasing won't help -- there's already not enough metal to hold the cups, and taking more off isn't going to improve that.

The best solution (short of replacing the fork or steer tube) is to fill the damaged section with molten brass, and then cut new threads into the brass. Brass isn't as strong as steel, but if you're careful to keep the headset properly adjusted it should hold up well enough. I've done this to many forks over the years and never had one come back because the threads failed.

Or buy a new one. https://www.jensonusa.com/Bicycle-Rig...on-Hi-Ten-Fork which might even be the less inexpensive way in the long run.

Poop.

The race /was/ holding on there pretty tight when I removed it and the headset was not sloppy when I first examined it.

I do have a framebuilding friend in town who could probably do the brass. Would that kind of heat at the far end of the steerer have any effect on the paint at the top of the fork legs?

What about building up the threads with epoxy?

No, the heat shouldn't affect the paint at all. I wouldn't trust epoxy to hold, and besides, you want to be able to adjust the headset.