Colnago fork woes
 

[Hoping some of the finest minds, like Bulgie can help.]

I keep finding Colnagos with fork problems. One (1978) has the proper matching fork, both number stamped but the fork (stack) is too cut down to thread a campy headset. My Colnago Tandem came with a Benotto fork. Sigh.


Recently I found a "Playing Cards" 1970 Colnago frame for cheap. It came with a De Rosa fork (?!?). The resale of the fork will pay for the restoration. And parts!!


After searching for a proper fork with the two holes on the sides of the crown, I found this rusty fork. The condition didn't scare me because I wasn't planning on chroming the crown anyway.

Then I noticed something peculiar. The threads had been ground off.

Let me repeat….

THE THREADS HAD BEEN GROUND OFF!!!

https://cimg2.ibsrv.net/gimg/bikefor...eba24d1a0.jpeg
https://cimg3.ibsrv.net/gimg/bikefor...7b864f4b4.jpeg
https://cimg4.ibsrv.net/gimg/bikefor...153931a1e.jpeg
https://cimg5.ibsrv.net/gimg/bikefor...20b1fcb61.jpeg
Eeek


I have been racking my small brain to find a solution. Only thing I've come up with, and this is a long shot. Could I have it lathed with French threads? French forks must be smaller due to their quill stems being smaller. Then I only need to find a French threaded campy top nut.

Would that work or any other ideas?

Be sure to descale and take a straight edge to it. I see the very end of where the threads were.

if looks straight might be threaded to French, BUT hand held dies are not really to be used to cut threads from scratch.
possibly a VAR tool as the examples I have seen are adjustable in circumference.

If successful, you would need two French threaded parts, top race and nut.

i really doubt a machinist would turn it down to 25x 1 threading. Think about how it would be held and the swing and imbalance of theblades.

cool that you were able to find

Are you sure that it’s taken down, or is it really tall and broken at the base of threading.

I'm thinking like Mr. 66 . It looks like it snapped at the last threads. I think the difference in diameter your seeing is what's left of the chrome plating on the bottom half of the steerer. All chromed forks I've seen were only chromed part way up the steerer.

Looks like a good candidate for a steerer cut and paste :)

I saw a thread here some time ago (maybe Gugie?) about cutting / sleeving and brazing a replacement steerer on without interfering with fork crown etc .

Is this a Colnago fork or a fork for a Colnago frame?

I’d have thought the number of 1970s Colnago forks built with French diameter steerer tubes would have been near zero.

I have a Colnago fork just like the one photoed. It was one a bike that that had had seen little maintenance. Steerer tube broke one day, at base of stem that was positioned at bottom of threads. Was told that this happens if stem is never removed or or height changed. Expect that this fork got similar treatment.

nothing has snapped. it was tall. it came off a 60ctc colnago.

It is italian through and through. Previous owner ground the threads off to use a Threadless/clamp-on stem. Special place in hades I tell ya.

My thought is to have it French threaded for a French headset. Then I can still use it in a 56ctc bike.

It’s a little outside my field of (limited) expertise but I don’t think that story checks out.

The beginnings of some threading is visible at the top of the steerer.

If it were previously threaded the threads would have been cut at least 0.5mm into the steerer, meaning once ground off the remaining steerer would be no greater than 24mm OD. Unless they were filled rather than ground off but there’s no sign of that in the photos.

I stand by the view that the steerer has been cut, or broke, at the start of the threads. It may well have been used with a threadless headset thereafter. Not uncommon to cut the threaded end off a long fork steerer to use threadless on frame with a short head tube. Much easier than cutting more thread.

I bet it wasn’t 25.0mm OD…

This Italian fork is from an Atala and it is in great shape (the yellow one). I can put in on the For Sale forum if interested - cheap...
https://cimg4.ibsrv.net/gimg/bikefor...1c27382df4.jpg
https://cimg5.ibsrv.net/gimg/bikefor...8fd2782134.jpg

Just get the steerer tube replaced. NBD

Happens all the time. Mr. Litton did a Masi for me.

Nobody is willing to do fork steering tube work. Insurance reasons.

I'm not convinced. I can't say what the real situation is, but it isn't that. You can't grind the threads off a steerer and then clamp a stem to the resulting uneven, random-sized surface. It would have to be way smaller than your caliper shows, to make all the thread go away — the minor diameter of the thread is around 1.5 mm smaller i.e. somewhere around 24 mm. That's how far you have to "grind" a steerer down to make the existing threads all go away.

Plus we can see in the pic that the original threads aren't gone, they're still there at the top.

Again I can't tell what all is going on here. I'd need to inspect the fork myself to say anything definitive.

I will say though, threading it to French is unsafe, for reasons. For one, the inside diameter is smaller on a French steerer. Taking a steerer down on the outside, while keeping the larger inside diameter, makes the wall thinner. Steerers do break sometimes and the results can be catastrophic as in dead. There are other reasons this is a bad idea but that big one should be enough.

Has Bernie Mikkelson retired? He used to do 'em.

If you're considering replacing the steering tube, I would just run a 1" die on the existing one. I bet it will be fine.

I checked the internal diameter of a 1" headset adjustable cup and I got 24.48mm. So, I really doubt those threads were ground down to 25.0mm. They would've needed to go further to lose all evidence of the threads.

My vote is that someone shoddily cut off the threaded portion, as evidenced by the presence of threads at the top and the crooked edge.

I had a repair done to a late ‘70’s Mexico steering tube. Jack Trumbull at Franklin Frames in Newark Ohio did the work. Excellent repair and his price was very reasonable. Might be worth contacting him to see if he’s willing to take on the work.

We need more pics of your Weimaraner

I love those who are chiming in. Like I said, my small brain could not figure out a way to save and use these.

To be clear, these are Italian. COLNAGO. they were Italian threaded. Italia specs.

I also love all the speculation. Like when I actually hold calipers and then there is doubt on measurement.

Yes, the top was crudely hacked off by some kid with zero hacksaw skills. Somehow in his ace machinist skills he left some threads.

No, nothing was broken off. This is a tall steering tube. I doubt it was available any taller.

Yes, the threads were ground off. You can see the difference from where the paint (primer really) ends and the long lost threads were.

I'm sending it north to have it professionally assessed and see if anything can be done.

I wish it was as simple as having a new steerer welded in place. Zero people are willing to do that anymore due to insurance regulations.

Lastly,

Yes, Greta is a good sport.

If you're okay with shipping, you could try contacting Dale Saso down in San Jose. Pretty sure he'd be up for that. And possibly John Fitzgerald. I recently talked to him about it for a bike. He was on the fence, kinda, but mostly against the practice on a client's bike. Though said he would do it for his own bike, or a close friend's.

Jack at Franklin will. And do the chrome. And do the paint.

nice work from what I have seen.
at prices that meet and are below coastal prices.