TullySteve

(New here, also posted in mechanics): I decided to turn my beat up 1972 Moto Grand Record into a 1x with a new (probably hand-done) paint job. It's been hanging in the garage for over 10 years, loads of miles prior to that. The fork tube threads apparently got gnarled either by the Mafac brake bracket, or spacer, or something else. When backing off the top headset adjustable cup, I'm running into a jam and can see the bad threads. I dare not go further without advice. LBS does not have French taps & dies to re-cut threads. I'm in Syracuse NY area. Some have said to go ahead and start slowly working the cup off with a bit of WD40 and the harder steel of the cup may power through. I'm skeptical. If the fork & headset won't work, the project will just be abandoned. Any experience or advice welcome. Maybe I could find a LBS within an hour or so that has the old dies?

WGB 

IIRC Andrew R Stewart is either in Rochester or Syracuse. He should know someone who can help you.
Perhaps PM him directly.

rustystrings61 

My inclination, based on my experience detailed below, is to use some decent lubricant and gently working the adjustable cup upwards should reshape the threads successfully.

FWIW, I have an Allegro - Swiss, therefore metric threads, and the fork steerer on mine just so happens to be the classical French Nervor 22.0 inner diameter, 25.0 outer. A previous owner had removed the stock headset (probably a Stronglight P3, as the stack height was really low) and had hamfisted on an Italian Campagnolo NR headset minus spacers, washers, etc., achieving a class D fit and munging up the threads. The crown appeared to have been cut to 26.4, as well. What I wound up doing was acquiring a basic cheap Motobecane headset and using the top half of it to reshape the munged-up threads. It worked and has held for some time now. I used the top half of the budget steel O.E.M. headset with its French threads along with the bottom half of a basic Tange unit to accommodate the 26.4 mm crown race seat.

Someone, and I want to say it was our own Chas. Colerich/verktyg has written somewhere that Motobecane's O.E.M. headsets were actually made by Stronglight. The ones I've handled felt pretty well made and robust.

Ex Pres 

I bought a cheap 25x1 die (from China) off ebay and successfully repaired threads myself on an old fork. Figured the die won't see much more use, so cheap was OK.

I don't think it was listed under bicycle specific tools, just as a generic tool, whatever ebay category that might be. Just type in 25x1 die into search.

TullySteve

Thanks for the quick and varied replies!. I'm going to start by letting my trusty LBS at least look at it, then decide. Upon basic cleanup, it is a Stronglight headset. I am trying to make this a mostly DIY affair. My LBS does have the Stronglight-specific crank puller so I can avoid paying full price for a one-use tool. He said it was the first tool his dad bought him back then, and he still has it in good shape for the once-a-decade need.

TullySteve

Cannot PM him as a newbie member until I have more posts. But I can reach out somehow if other solutions don't solve my problem.

Charles Wahl

While you can find a 25 x 1 die from China on eBay for $25 or so (search "M25x1 die"), I'd be concerned that the die might not clean up much because you can't thread the die fully onto the steerer, and thus get the the "lead-in" on the threading of the die past the damaged "band" of threads on the steerer (the smaller diameter teeth that finalize the cutting not reaching the damaged "band" because the top cup is still there, hard up against the damage). If one side of the die has no "lead-in" (threads "tight" right up to the face of the die) that might help -- obviously I'm no tool-and-die expert.

If you have a fine-toothed needle file, or even an Exacto #11 or box cutter blade in a solid holder, I'd try to open up the munged threads by running the blade in the bottoms of the threads, under good light, with a big magnifying glass if you have one (three handed-job).

Now is when a bike shop with expert service staff is a real boon, and everywhere is wide-open again in NY now, right? (except for the "certain restrictions" that remain in place, but are unspecified)

dedhed

We can tag Andrew R Stewart so he will see this.

3alarmer 

....aye, there's the rub. I actually have one of the last known official French fork threading dies and the handle it fits in, but I am dubious it would help you in your situation. If you analyze the issue, I think you'll agree that the spot where the threads on your fork are bunged up have served no mechanical purpose over the years you've had the bike and ridden it like this. Below that bunged up spot, is where the money threads are...the ones that hold the top adjustable headset race in place. Above that spot, you certainly need at least a few good threads to hold the top nut in position, where it clamps down on whatever spacers/washers you are using between it and the top race.

Everything else on the fork steerer, threadwise, is just gravy. Were it me, I'd carefully work that adjustable steel Stronglight headset race upward, using some sort of cutting oil as the lubricant, of whatever you have that's a heavy viscosity in the absence of real cutting oil suitable for steel ( which is pretty cheap to buy anyway). It shouldn't affect the threads where your top race now sits, may or may not straighten out the ones that are damaged, and as long as you are careful right at the top to keep it going in the existing threads, shouldn't hurt those either. If it gets really stuck in the banged up portion, I'd be tempted to file those threads with a cleanup file...which is also not terribly expensive.

nlerner

I don’t think the tag function has worked for months. Instead, you need to include the ampersand: @Andrew R Stewart for notification to happen.

oneclick 

Just use the race and that'll clean up the threads just fine. Go slow, use a bit of any old oil (it's just for lube, you don't need/want "cutting oil"), The race is likely far harder than the steerer. Getting a die is not a good idea, it will be hard to start correctly and will cut away any metal of the thread that has been bent into the wrong shape/place. The race will just bend it back.

EDIT - it's a steel headset, right?

Reynolds 

I'd try unscrewing the cup as much as possible by hand and see if the balls can come out (this could work if they are loose, not if in a retainer), then screwing the cup back as far as it will go, so you can see more threads, and correct them using a very small triangle file.

merziac

I use a right angle pic to scribe the threads back into shape as best I can then use a thread chaser very carefully and slowly with anti-seize, 1 step forward, 2 steps back and so on.

That being said, I have not had a really bad example of steerer threads but I have used anti-seize and a race to reform them, patience is key, 1 step forward, 2 steps back.

I have restored horrible BB threads many times with this method and both production and self made chasers.

This has also saved my bacon at the drag strip a couple of times.

oneclick 

I should point out that a very small bit of damage can make it quite difficult to turn a large fine thread such as these. All you need is a bit of metal from the crest of the thread bent far enough that it crosses the root and lies in the path of the start of the thread on the race as that is turned closer to the damage. The race thread can ride up on the bit of metal, forcing the far side of the threads tight against the steerer, and the friction goes way up and stays up. That's why you need the lube, and luck - obviously such a folded-over crest can happen to be oriented such that the advancing thread forces it back; when that happens, the resistance is high but falls quickly after the metal isn't in the way anymore.

TullySteve

Thanks for all the ideas! A fine pic and sharp fine file, great light and $5 "jeweler's loop" from Harbor Freight cleaned up the threads to start. Then good lube and gradually working the cup off worked!