Threaded headset Top race cup won't unscrew
#51
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However, I managed to take it off several hours ago. I went to my LBS where they have a proper vise which I could use. Once the fork was clamped into the vise, it was a matter of applying quite some force to remove it. But it got loose in the end! My theory got actually approved. The steerer tube got kinda expanded that's why the race wouldn't move. The guy at the shop chased the threads with a tap so the fork should be fine to use. However, when I got home I got to think whether he used the right tap for French threading
The obsolete French size is 25mm x 1mm. The more recent ISO size is 1" x 24TPI. If you think about this, if you used an ISO die on a French-threaded fork, you'd be taking 0.4mm off the diameter or 0.2mm off the radius. Both threads use a 60° thread profile, so the original thread depth of about square root of 3 over 2 times 1mm would be 0.866 mm. You'd be taking 25% of the metal off the threads, you'd be generating a hell of a lot of metal filings ("swarf") and (IMHO) you'd have as hard a time getting the die started and turning it as you had removing the race.
Because this difference is pretty obvious, I suspect that your bike shop guy did not use the wrong die and you should be ok. Does the race screw onto the fork easily? If so, your fine. When you re-install, remember that you don't have to apply a lot of torque to the race. Enough to get the pin under one of the holes in the washer conveniently. And use grease on the threads to prevent corrosion, rust, and the threads locking up over another 45 year period. The bike should be good to ride in 2073!
Taps (long skinny things) and dies (discs with holes):
Last edited by WizardOfBoz; 11-24-19 at 10:47 AM.
#52
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Terminology: If he chased the internal threads on the bearing race, he would use a tap. If he chased the external threads on the fork, then he used a die. Because bearing races are generally hardened, it would be more likely that he ran a die over the fork.
The obsolete French size is 25mm x 1mm. The more recent ISO size is 1" x 24TPI. If you think about this, if you used an ISO die on a French-threaded fork, you'd be taking 0.4mm off the diameter or 0.2mm off the radius. Both threads use a 60° thread profile, so the original thread depth of about square root of 3 over 2 times 1mm would be 0.866 mm. You'd be taking 25% of the metal off the threads, you'd be generating a hell of a lot of metal filings ("swarf") and (IMHO) you'd have as hard a time getting the die started and turning it as you had removing the race.
Because this difference is pretty obvious, I suspect that your bike shop guy did not use the wrong die and you should be ok. Does the race screw onto the fork easily? If so, your fine. When you re-install, remember that you don't have to apply a lot of torque to the race. Enough to get the pin under one of the holes in the washer conveniently. And use grease on the threads to prevent corrosion, rust, and the threads locking up over another 45 year period. The bike should be good to ride in 2073!
Taps (long skinny things) and dies (discs with holes):
The obsolete French size is 25mm x 1mm. The more recent ISO size is 1" x 24TPI. If you think about this, if you used an ISO die on a French-threaded fork, you'd be taking 0.4mm off the diameter or 0.2mm off the radius. Both threads use a 60° thread profile, so the original thread depth of about square root of 3 over 2 times 1mm would be 0.866 mm. You'd be taking 25% of the metal off the threads, you'd be generating a hell of a lot of metal filings ("swarf") and (IMHO) you'd have as hard a time getting the die started and turning it as you had removing the race.
Because this difference is pretty obvious, I suspect that your bike shop guy did not use the wrong die and you should be ok. Does the race screw onto the fork easily? If so, your fine. When you re-install, remember that you don't have to apply a lot of torque to the race. Enough to get the pin under one of the holes in the washer conveniently. And use grease on the threads to prevent corrosion, rust, and the threads locking up over another 45 year period. The bike should be good to ride in 2073!
Taps (long skinny things) and dies (discs with holes):
#53
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Alex, It is sobering to note that a lot of folks in the Netherlands write using better English than some of us "'muricans." I grew up working in a machine shop (and my background is engineering) so I thought I'd add the definitions for others.
I hope you feel better. Hope also to hear that your fork is working well. The headset with a pin is a unique design and it was fun to learn about. (Or maybe, fun to relearn what I forgot from 40 years ago....
I hope you feel better. Hope also to hear that your fork is working well. The headset with a pin is a unique design and it was fun to learn about. (Or maybe, fun to relearn what I forgot from 40 years ago....
Last edited by WizardOfBoz; 12-01-19 at 10:01 AM.
#54
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I made an error in the note above (quoted below). ISO threads are 1" x 24tpi. The old French threading is 25mm x 1mm pitch. So running a larger diameter ISO die over a French steer tube would not remove as much metal as I thought, but it would (if centered) cut weird 0.466mm grooves in the French steerer ata 1mm pitch. In any case, I think it would be noticeable and hard to start the die evenly.
Thanks to Mad Honk for pointing this out to me (being the discrete, generally helpful and considerate person he is, he did it in a PM, but if I'm wrong I'm wrong). Thanks, MH!
Thanks to Mad Honk for pointing this out to me (being the discrete, generally helpful and considerate person he is, he did it in a PM, but if I'm wrong I'm wrong). Thanks, MH!
The obsolete French size is 25mm x 1mm. The more recent ISO size is 1" x 24TPI. If you think about this, if you used an ISO die on a French-threaded fork, you'd be taking 0.4mm off the diameter or 0.2mm off the radius. Both threads use a 60° thread profile, so the original thread depth of about square root of 3 over 2 times 1mm would be 0.866 mm. You'd be taking 25% of the metal off the threads, you'd be generating a hell of a lot of metal filings ("swarf") and (IMHO) you'd have as hard a time getting the die started and turning it as you had removing the race.
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Wiz,
I am not the gentle person you suspect that I am. As Rob my watch repair person says: "That's no gentleman, it's Dave". But I wonder what the change over date was for the change from Whitworth threads to the newer BSA standards. And the cutting of the steerer tube deeper with the 60* pitch would likely make the threads deeper, but would likely still have some purchase for the French threads but just not as complete a match as would be best for all purposes. I doubt though, that the change would be catastrophic for the OP if the wrong die set was used.
As to the starting of the die, I think it would likely start easily as the dies are cut to a taper for easier cutting. And the arms on the die holders are fairly long which would be some pretty great leverage that would not be noticed by the operator when taking just a few thousandths of an inch out a set of threads. I see the same, when chasing threads with a burr on them for small parts. JMHO, MH
I am not the gentle person you suspect that I am. As Rob my watch repair person says: "That's no gentleman, it's Dave". But I wonder what the change over date was for the change from Whitworth threads to the newer BSA standards. And the cutting of the steerer tube deeper with the 60* pitch would likely make the threads deeper, but would likely still have some purchase for the French threads but just not as complete a match as would be best for all purposes. I doubt though, that the change would be catastrophic for the OP if the wrong die set was used.
As to the starting of the die, I think it would likely start easily as the dies are cut to a taper for easier cutting. And the arms on the die holders are fairly long which would be some pretty great leverage that would not be noticed by the operator when taking just a few thousandths of an inch out a set of threads. I see the same, when chasing threads with a burr on them for small parts. JMHO, MH
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Alex, It is sobering to note that a lot of folks in the Netherlands write using better English than some of us "'muricans." I grew up working in a machine shop (and my background is engineering) so I thought I'd add the definitions for others.
I hope you feel better. Hope also to hear that your fork is working well. The headset with a pin is a unique design and it was fun to learn about. (Or maybe, fun to relearn what I forgot from 40 years ago....
I hope you feel better. Hope also to hear that your fork is working well. The headset with a pin is a unique design and it was fun to learn about. (Or maybe, fun to relearn what I forgot from 40 years ago....
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I finally had some time to check the fork once again. The threads on the steerer do not look that good as they seemed at first. The best I can describe them is not being even. Moreover, I could thread an English headset upper race easily all the way down the threads So it wasn't a proper die! The problem is that the English race has some play once threaded.
Do I have a problem here?
Do I have a problem here?
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I finally had some time to check the fork once again. The threads on the steerer do not look that good as they seemed at first. The best I can describe them is not being even. Moreover, I could thread an English headset upper race easily all the way down the threads So it wasn't a proper die! The problem is that the English race has some play once threaded.
Do I have a problem here?
Do I have a problem here?
Oh, and scrape all that fuzz off the threads.
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So is the English threaded cup just for test, or are you planning on using it? That might be hard: remember, the French steerer tube is 25mm OD (outside diameter), and an English thread is made for a 25.4mm OD. So, as a bit of encouragement, you would expect the English cup to be loose! In fact, given the difference in diameter you may have the correct thread and the diameter difference is allowing you to put the English cup on. In any case, without heroic effort you must use a French thread cup on this fork.
How does the original cup fit? How well does it fit? So now you have one advantage of that French system, with the little post and the washer with holes. It might help prevent the cup from getting loose and progressively unscrew.
Again, the It looks to me like the threads start out pretty close to ok but as the die progressed, the roots (low points) and crests (high points) of the thread got out of synch, so the die was cutting roots where the thread crests should be. Given the difference between a 24 tpi (pitch = 1/24 inch, or 0.041667"/1.0583mm pitch) and 1mm pitch , it would take about 8.5 threads for the roots and crests to overlap (probably more because there's a little slop especially given the larger diameter of the English die). Then the roots and crests are in synch after 17 threads. Can you see this?
The ID of the English die is calculated approximately by using 25.4 mm nominal OD of English tube. The theoretical depth of the thread is 1/24 inch * 25.4mm/inch * square root (3)/2 = 0.917mm. Typically roots aren't cut "sharp", that is there's about 1/8 of the pitch that's not cut. So use 0.802 mm. We have threads on both sides, so the roots in English threads are 1.604 mm less than nominal. So the English die at its deepest cut left a diameter of 23.8mm. To approximate how much you cut off the crests of the actual fork is easy: 1/2 of 1.2mm, or 0.6mm. The French thread height is 0.758mm, so at its worst point the die removed about 80% of the thread.
If it was an English die on the French thread, the whole setup was weakened. Some sections of the thread should be pretty normal (where the die and fork threads were in synch) and some sections will be weak. Perhaps someone has experience with such a thing but if your French cup doesn't fit on very well or at all I think its time to get a new fork. If the French cup fits, you may be able to ride it (in this case the locknut may be over a a "strong" section and the cone over a weak/overcut section or vice versa. It may work. Also time to educate your bike shop about being careful with vintage bikes that don't necessarily follow common standards.
How does the original cup fit? How well does it fit? So now you have one advantage of that French system, with the little post and the washer with holes. It might help prevent the cup from getting loose and progressively unscrew.
Again, the It looks to me like the threads start out pretty close to ok but as the die progressed, the roots (low points) and crests (high points) of the thread got out of synch, so the die was cutting roots where the thread crests should be. Given the difference between a 24 tpi (pitch = 1/24 inch, or 0.041667"/1.0583mm pitch) and 1mm pitch , it would take about 8.5 threads for the roots and crests to overlap (probably more because there's a little slop especially given the larger diameter of the English die). Then the roots and crests are in synch after 17 threads. Can you see this?
The ID of the English die is calculated approximately by using 25.4 mm nominal OD of English tube. The theoretical depth of the thread is 1/24 inch * 25.4mm/inch * square root (3)/2 = 0.917mm. Typically roots aren't cut "sharp", that is there's about 1/8 of the pitch that's not cut. So use 0.802 mm. We have threads on both sides, so the roots in English threads are 1.604 mm less than nominal. So the English die at its deepest cut left a diameter of 23.8mm. To approximate how much you cut off the crests of the actual fork is easy: 1/2 of 1.2mm, or 0.6mm. The French thread height is 0.758mm, so at its worst point the die removed about 80% of the thread.
If it was an English die on the French thread, the whole setup was weakened. Some sections of the thread should be pretty normal (where the die and fork threads were in synch) and some sections will be weak. Perhaps someone has experience with such a thing but if your French cup doesn't fit on very well or at all I think its time to get a new fork. If the French cup fits, you may be able to ride it (in this case the locknut may be over a a "strong" section and the cone over a weak/overcut section or vice versa. It may work. Also time to educate your bike shop about being careful with vintage bikes that don't necessarily follow common standards.
Last edited by WizardOfBoz; 12-08-19 at 11:06 PM.
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So is the English threaded cup just for test, or are you planning on using it? That might be hard: remember, the French steerer tube is 25mm OD (outside diameter), and an English thread is made for a 25.4mm OD. So, as a bit of encouragement, you would expect the English cup to be loose! In fact, given the difference in diameter you may have the correct thread.
In any case, without heroic effort you must use a French thread cup on this fork. How does the original cup fit? How well does it fit? So now you have one advantage of that French system, with the little post and the washer with holes. At the very least the cup shouldn't get loose and progressively unscrew.
....
In any case, without heroic effort you must use a French thread cup on this fork. How does the original cup fit? How well does it fit? So now you have one advantage of that French system, with the little post and the washer with holes. At the very least the cup shouldn't get loose and progressively unscrew.
....
If the original threaded race seems to thread on OK, then you don't have a problem.
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#61
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I finally had some time to check the fork once again. The threads on the steerer do not look that good as they seemed at first. The best I can describe them is not being even. Moreover, I could thread an English headset upper race easily all the way down the threads So it wasn't a proper die! The problem is that the English race has some play once threaded.
Do I have a problem here?
Do I have a problem here?
In short, you need to use a French thread headset with that fork. Or, replace the fork with an English thread fork and use an English thread headset.
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Thanks for your replies! I will visit that same LBS to see which dies they have there. In fact, they have a lot of old VAR tools so I hope that the right die is just laying somewhere around there.
This bike in not a keeper I just what to put it back together and sell it to someone else. I am working on a very similar PR-10 which is in better condition and which I am planning to keep. This is the thread for both bikes in case you're interested.
I'll report once I have some progress with the fork.
This bike in not a keeper I just what to put it back together and sell it to someone else. I am working on a very similar PR-10 which is in better condition and which I am planning to keep. This is the thread for both bikes in case you're interested.
I'll report once I have some progress with the fork.
#63
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I am in the same boat. Does the washer on top of the decagonal nut need to be pulled or screwed off? It doesn't budge a bit. Maybe it's a keyed washer. I am at a loss. Thanks so much ahead of time!
Last edited by Bladeputr13; 04-30-20 at 04:37 PM. Reason: Wrong word
#64
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To disassemble you'd be best using a locknut wrench to unscrew the locknut. Then the washer should pull straight off. Then you can unscrew the top upper race off. Be careful - if the setup uses loose ball bearings you want to be prepared to catch 'em. Note: if loosen the top bearing race, it allows the fork to move, and so it can be that ball bearings from BOTH the top and the bottom fall out. If you do it over a light-colored shop towel and are careful, you should be able to recover all bearings. Of course, if the bearings are in retainers, its easier.
Last edited by WizardOfBoz; 04-30-20 at 08:39 PM.