Repairing threads on French steerer tube?

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its_all_calypso
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Joined: 14 Oct 2021, 9:19am

Repairing threads on French steerer tube?

Post by its_all_calypso »

Hi all,

I began rebuilding a vintage French bike recently and, after finally sourcing a suitable headset, realised that the adjustable cup won’t go past THAT point (photo - https://imgur.com/a/S9PP2Qx). As you can see it doesn’t look too bad but you can see that a section of the threads are worn and slightly wonky, probably from a loose headset. Is this a simple fix or is my project doomed? I’ve already invested a bit of time into this bike and would hate to have to scrap it. I probably should have checked the threads first (the bb is fine) - lesson learned.

Thanks in advance!
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531colin
Posts: 16083
Joined: 4 Dec 2009, 6:56pm
Location: North Yorkshire

Re: Repairing threads on French steerer tube?

Post by 531colin »

A thread "chaser" suitable for repairing damaged threads can be made by making saw/file cuts across the thread on a suitable (spare) nut....but you won't have one of them?

Or there are headsets like this

ImageIMG_5367 by 531colin, on Flickr

ImageIMG_5368 by 531colin, on Flickr

designed for damaged steerers ....although I have only seen them for English sizes.

I don't know if its english size tube....I suspect it is.....ie. inch external, seven eighths inch internal (22.2mm ?)
If it is, its pretty easy to cut the steerer back, sleeve it internally (eg with a bit of stem) and add a new top bit of steerer; you could then make it threadless, or English thread.

Image005 by 531colin, on Flickr
rjb
Posts: 7200
Joined: 11 Jan 2007, 10:25am
Location: Somerset (originally 60/70's Plymouth)

Re: Repairing threads on French steerer tube?

Post by rjb »

Thats a good job 531, not sure my brazing skills are up to that. Can you give us the link to your original post of how you did this please. :D
At the last count:- Peugeot 531 pro, Dawes Discovery Tandem, Dawes Kingpin X3, Raleigh 20 stowaway, 1965 Moulton deluxe, Falcon K2 MTB dropped bar tourer, Rudge Bi frame folder, Longstaff trike conversion on a Giant XTC 840 :D
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531colin
Posts: 16083
Joined: 4 Dec 2009, 6:56pm
Location: North Yorkshire

Re: Repairing threads on French steerer tube?

Post by 531colin »

Not sure I posted it in detail.
You need a bit of stem or 7/8th inch tube to sleeve inside the steerer. Clean up all the cuts and the tube fits well enough to jig the steerer straight enough.
I drilled maybe 6mm holes to run silver solder in, 2 above and 2 below the join.
Need to get it hot enough so the work melts the spelter, not the flame melting the spelter. You can see the spelter appear at the ends of the sleeve tube inside the steerer, and you know its run well enough.
I used 2 blowtorches running MAPP gas

Close-up......

Image003 by 531colin, on Flickr
pete75
Posts: 16370
Joined: 24 Jul 2007, 2:37pm

Re: Repairing threads on French steerer tube?

Post by pete75 »

A bit pricey but you could probably get a lot of the cost back by selling it once it's no longer needed.
https://www.ebay.co.uk/itm/New-35mm-x-1 ... 3789528719
'Give me my bike, a bit of sunshine - and a stop-off for a lunchtime pint - and I'm a happy man.' - Reg Baker
rogerzilla
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Joined: 9 Jun 2008, 8:06pm

Re: Repairing threads on French steerer tube?

Post by rogerzilla »

You might be able to reform the threads with a scratch awl or other pointed tool, depending how hard the steel is. Once they're good enough to get a hardened steel race up and down with plenty of oil, they will bend further into shape.
9494arnold
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Joined: 21 Jan 2007, 3:13pm

Re: Repairing threads on French steerer tube?

Post by 9494arnold »

Try putting the top race (adjustable cup I think you refer to? ) on and turn it down with a proper headset spanner or the biggest adjustable you can get your hands on. As you get towards the damaged bit,make sure there's plenty of oil or grease on the threaded bit (keep it away from the spanner! ) and just keep turning.
I did this on one of mine, (a vintage collectors frame) it worked a treat.
Make sure you start in the thread properly, I fear that your previous top race may have been cross threaded over the tab washer depression at the top of the Fork Column , and it has only "bitten' below the depression.
PhilD28
Posts: 352
Joined: 26 Sep 2016, 8:31am

Re: Repairing threads on French steerer tube?

Post by PhilD28 »

Thread files are the usual way in engineering of restoring a damaged odd size thread. Assuming you know what pitch it is you can buy them online, such as here, https://www.frost.co.uk/metric-thread-file/ , make sure you check if the pitch you need is in the range of any particular file.
I’ve had similar metric and imperial versions for over 40 years and they’ve earned their keep on countless jobs.
PhilD28
Posts: 352
Joined: 26 Sep 2016, 8:31am

Re: Repairing threads on French steerer tube?

Post by PhilD28 »

I can’t remember the pitch of French steerer tubes offhand but 1mm rings a bell, you should check and if it is, this thread file should do the trick as it includes 1mm pitch in its range.

https://www.amazon.co.uk/Thread-Restora ... 83&sr=8-12
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