Go Back  Bike Forums > Bike Forums > Bicycle Mechanics
Reload this Page >

Threaded headset Top race cup won't unscrew

Notices
Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

Threaded headset Top race cup won't unscrew

Old 11-23-19, 10:59 PM
  #51  
WizardOfBoz
Generally bewildered
 
WizardOfBoz's Avatar
 
Join Date: Aug 2015
Location: Eastern PA, USA
Posts: 3,036

Bikes: 2014 Trek Domane 6.9, 1999 LeMond Zurich, 1978 Schwinn Superior

Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 1152 Post(s)
Liked 340 Times in 250 Posts
Originally Posted by alexnagui
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
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):


Last edited by WizardOfBoz; 11-24-19 at 10:47 AM.
WizardOfBoz is offline  
Old 12-01-19, 09:18 AM
  #52  
alexnagui
Full Member
Thread Starter
 
alexnagui's Avatar
 
Join Date: Oct 2017
Location: Rotterdam, The Netherlands
Posts: 361
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 157 Post(s)
Liked 113 Times in 64 Posts
Originally Posted by WizardOfBoz
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):

Yeah, I realized that I didn't use the right term after I had written my post. It was a die of course which was used on the fork steerer tube threads. I still gotta check the threads, I was sick for a while so haven't had any time for bikes. But I believe that they should be fine after reading the comments here
alexnagui is offline  
Old 12-01-19, 09:47 AM
  #53  
WizardOfBoz
Generally bewildered
 
WizardOfBoz's Avatar
 
Join Date: Aug 2015
Location: Eastern PA, USA
Posts: 3,036

Bikes: 2014 Trek Domane 6.9, 1999 LeMond Zurich, 1978 Schwinn Superior

Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 1152 Post(s)
Liked 340 Times in 250 Posts
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....

Last edited by WizardOfBoz; 12-01-19 at 10:01 AM.
WizardOfBoz is offline  
Old 12-01-19, 05:04 PM
  #54  
WizardOfBoz
Generally bewildered
 
WizardOfBoz's Avatar
 
Join Date: Aug 2015
Location: Eastern PA, USA
Posts: 3,036

Bikes: 2014 Trek Domane 6.9, 1999 LeMond Zurich, 1978 Schwinn Superior

Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 1152 Post(s)
Liked 340 Times in 250 Posts
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!

Originally Posted by WizardOfBoz
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.
WizardOfBoz is offline  
Old 12-01-19, 05:53 PM
  #55  
Mad Honk 
Senior Member
 
Join Date: May 2019
Location: Bloomington, IN
Posts: 2,939

Bikes: Paramount, Faggin, Ochsner, Ciocc, Basso

Mentioned: 114 Post(s)
Tagged: 0 Thread(s)
Quoted: 1285 Post(s)
Liked 1,838 Times in 1,111 Posts
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
Mad Honk is offline  
Old 12-08-19, 10:31 AM
  #56  
alexnagui
Full Member
Thread Starter
 
alexnagui's Avatar
 
Join Date: Oct 2017
Location: Rotterdam, The Netherlands
Posts: 361
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 157 Post(s)
Liked 113 Times in 64 Posts
Originally Posted by WizardOfBoz
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....
​​​​​​You're right about the Dutch, they are indeed very good at English. I am not actually from here myself so that does not apply to me
alexnagui is offline  
Old 12-08-19, 10:32 AM
  #57  
alexnagui
Full Member
Thread Starter
 
alexnagui's Avatar
 
Join Date: Oct 2017
Location: Rotterdam, The Netherlands
Posts: 361
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 157 Post(s)
Liked 113 Times in 64 Posts
​​​​​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?

alexnagui is offline  
Old 12-08-19, 11:48 AM
  #58  
AnkleWork
Senior Member
 
Join Date: Jan 2013
Location: Llano Estacado
Posts: 3,702

Bikes: old clunker

Mentioned: 13 Post(s)
Tagged: 0 Thread(s)
Quoted: 684 Post(s)
Likes: 0
Liked 104 Times in 82 Posts
Originally Posted by alexnagui
​​​​​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?

Maybe have the mechanic run the die upside-down to restore the metal that was removed. (HAW!)

Oh, and scrape all that fuzz off the threads.
AnkleWork is offline  
Old 12-08-19, 12:06 PM
  #59  
WizardOfBoz
Generally bewildered
 
WizardOfBoz's Avatar
 
Join Date: Aug 2015
Location: Eastern PA, USA
Posts: 3,036

Bikes: 2014 Trek Domane 6.9, 1999 LeMond Zurich, 1978 Schwinn Superior

Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 1152 Post(s)
Liked 340 Times in 250 Posts
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.

Last edited by WizardOfBoz; 12-08-19 at 11:06 PM.
WizardOfBoz is offline  
Old 12-08-19, 01:27 PM
  #60  
3alarmer 
Friendship is Magic
 
3alarmer's Avatar
 
Join Date: Nov 2010
Location: Sacramento, CA
Posts: 22,932

Bikes: old ones

Mentioned: 304 Post(s)
Tagged: 0 Thread(s)
Quoted: 26251 Post(s)
Liked 10,232 Times in 7,101 Posts
Originally Posted by WizardOfBoz
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.

....
...this, pretty much. If you try the original French threaded race on there and there's a problem, your best bet would be to look around for someone who actually knows about French threading on forks and has the old cutting die to thread one. (In all likelihood, this person will be old.) Then get him (or her) to run it down your fork threads. This will probably be enough that your bike will work OK.

If the original threaded race seems to thread on OK, then you don't have a problem.
3alarmer is offline  
Likes For 3alarmer:
Old 12-08-19, 01:50 PM
  #61  
JohnDThompson 
Old fart
 
JohnDThompson's Avatar
 
Join Date: Nov 2004
Location: Appleton WI
Posts: 24,936

Bikes: Several, mostly not name brands.

Mentioned: 153 Post(s)
Tagged: 0 Thread(s)
Quoted: 3571 Post(s)
Liked 3,368 Times in 1,916 Posts
Originally Posted by alexnagui
​​​​​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?
I don't see any egregious problem with the threads. That you can thread an English thread cup onto the fork is due to the fact that the larger diameter of the cup means that the threads don't fully engage with the steer tube. That's also the reason why there is "play" with that cup. If you were to ride the fork with that cup installed, the play would eventually destroy the threads on the steer tube.

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.
JohnDThompson is offline  
Old 12-10-19, 10:00 AM
  #62  
alexnagui
Full Member
Thread Starter
 
alexnagui's Avatar
 
Join Date: Oct 2017
Location: Rotterdam, The Netherlands
Posts: 361
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 157 Post(s)
Liked 113 Times in 64 Posts
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.
alexnagui is offline  
Old 04-30-20, 04:35 PM
  #63  
Bladeputr13
Member
 
Join Date: Oct 2015
Posts: 43
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 15 Post(s)
Liked 2 Times in 2 Posts
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
Bladeputr13 is offline  
Old 04-30-20, 08:06 PM
  #64  
WizardOfBoz
Generally bewildered
 
WizardOfBoz's Avatar
 
Join Date: Aug 2015
Location: Eastern PA, USA
Posts: 3,036

Bikes: 2014 Trek Domane 6.9, 1999 LeMond Zurich, 1978 Schwinn Superior

Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 1152 Post(s)
Liked 340 Times in 250 Posts
Originally Posted by Bladeputr13
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!
To assemble this (disassembly is reverse) , start at the top of the head tube with a pressed-in bearing race, the upper bearing bottom race. On top of that are well-greased ball bearings. Then you screw the upper bearing top race onto the fork. That's the thing that has the cool rounded "flattened globe" shape and has the (had to check) octagonal flats built in. On top of that is a keyed (at least it should be keyed) washer. All you see of that in the pic is a smooth round surface. On top of that is the locknut. It's round and has notches in it.

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.
WizardOfBoz is offline  
Old 04-30-20, 08:09 PM
  #65  
Bladeputr13
Member
 
Join Date: Oct 2015
Posts: 43
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 15 Post(s)
Liked 2 Times in 2 Posts
Thank you for your time, wizardofboz! Im going to give it a go first thing in the morning.
Bladeputr13 is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.