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vanhelmont

Just when I thought I had my '72 Super Corsa almost finished, I got stuck again with fork/headset problems. My frame came forkless, and I got a Raleigh Super Course fork of appropriate length, and with the appropriate crown. Some previous owner had clearly done something to the threads, and the ebay seller said the threads might need to be filled by brazing, and new threads cut.
I tried both British and French threads on it, and the British seemed to go on a little further than the French. Well, you don't expect French threads on a Carleton fork. When it came time to put on the headset and fork, the fork crown was 27 mm so I tried an old Tange steel JIS headset I had. Everything fit except the top race that should screw onto the fork. Since the chrome on the headset was already pitted, and the threads were already messed up, I used the vise grips to try to get it on, and it went most of the way, but stopped about 1 cm short.
Then I stopped to think and look at it more carefully. I got out my calipers, and the diameter is 25.0 mm, compared to 25.4 for another fork. Also, a lower part of the threads matched up with the mm lines on a ruler under the magnifying glass.
Conclusion: Somebody had cut French threads in this. Then later somebody forced on a British headset, and I did the same.

Nobody in Tampa seems to have a French thread die to clean up the threads. What do I do?

1. Look for another fork? I need about 240 mm steering tube, and haven't been about to find appropriate forks that long.
2. Get a steel French headset. I have the threaded parts of an alloy headset, so I can't put much force on it. Clean up the threads with a jeweler's file (already started, with a little progress) and force on the headset.
3. Fill in the threads with Silver/Copper/Zinc brazing alloy and get somebody to cut a British thread.
4. Any other ideas?

Dave

Gtane

Dave,

I would either fit a spacer or go for alternative forks, probably alternative forks.

Tim

verktyg

Dave,

have I got a deal for you... Well almost.

I have a fork from about a 61-62cm Gitane Tour de France with Simplex dropouts. It made of Reynolds 531 and has metric threads and a 27mm crown race seat. Only problem is the steering tube is only 230mm long.

It's in great shape except some light scratches in the top section of the blades where it was painted. Someone striped the paint off and it looks like they hit it with some Scotch-Brite.

There are several things that you can do to make this fork work. It was made to use a Stronglight P3 headset with around a 34mm stack height. Campy Nuovo Record headsets have a ~40mm stack height.

1. You could try to find a different metric headset.

A. Campy pre-1985 Nuovo Record Track and Gran Sport headsets have ~34mm stack height.

B. Tange makes or made a number of different headsets with short stack heights. You need to check them out carefully because I've seen different specs for the same models. Also Tange headsets can come with 26.4 and 27mm crown races.

C. You could also get a metric Stronglight P3 headset.

All of these show up regularly on eBay.

2. If you can find a competent LBS with the proper tools, you can have them face off the top and bottom of the head tube a few millimeters and the fork crown as needed to fit the headset of your choice.

The facing tool can also ream out the top and bottom of the head tubs as needed.

The fork crown can also be cut down from 27mm to 26.4mm as needed.

You should have all head tubes and fork crowns faced off any time you change a headset.

Here's what Sheldon Brown had to say about headsets:

http://sheldonbrown.com/gloss_ha-i.html#headset

These online sellers have metric headsets:

http://www.bicycleclassics.com/headsets.html

http://www.velo-orange.com/talealhe.html

PM me if you are interested in the fork. I may have a headset to fit too.

Chas.

vanhelmont

Thanks Tim and Chas,

I've been looking for forks, but nothing that looks right and is long enough has turned up on ebay until today. Somebody is selling a Raleigh fork that appears to be identical to the Super Course fork I have, except only the tips are chrome, so I'd either have to put a red fork on my blue bike, or go back to painting. I sort of like the chrome crown on the fork I have now.

Chas, if I got your fork I wouldn't have to paint it, but I'm not sure I could make it fit, especially if I need the spacer that holds the front brake cable for the MAFAC centerpulls.

I'm leaning toward making a French headset fit the fork. I used a file to clean up the first few threads so that the French headset can start to go on, and the threads where the upper cup would sit are in good shape, so I think I can make it work if I get a steel French headset. If that doesn't work, I'll think about another fork.

Dave

verktyg

Dave,

There's a tool called a thread file that makes thread repair easy. Here's a place that sells them online but you can find them lots of places.

http://www.sjdiscounttools.com/kas2670.html

There are several things that you should consider when your repair stripped threads on the steering tube. Inspect the tube and threads very carefully. It something doesn't look right, don't use the fork.

The wall thickness of the top of the steering tube is 1.5mm or less. The thread height of a 1.0mm pitch thread is approximately 0.6mm which means the tubing is 0.9mm or less thick (0.035") at the bottom of the threads.

The sharp V shape of a thread can create stress risers which can propagate cracks.

Notice how the diameter of the 25mm steering tube is larger than the actual thread diameter and how thin the tubing is at the flat area.

Many French bike manufacturers saved a few centimes (1/100 of a franc) buy using cheap steering tubes made of seamed plain carbon steel or even straight gage seamed carbon steel tubing with a sleeve brazed into them in the fork crown area. Rolling Eyes

Gitane usually used Reynolds steering tubes in their all Reynolds frames. They have "Reynolds 531" stamped into them.

Reynolds 531 is strong enough to withstand cracking better than carbon steels.

I've had a steering tube (as well as several cheap cast aluminum stems) fail while riding. The steering tube broke off at the top adjustable race in the headset. Fortunately the stem was still partially sticking in the steerer and I was able to safely stop the bike. Confused

Finally, try to find a fork with similar geometry as the original. If the blades or rake are longer or shorter it can drastically changed the ride and handling. Also brake reach can be an issue.

Gitane used different fork geometry over the years. They usually had enough clearance for fenders on the Super Corsa and TdF forks. In general the earlier models had more fork rake.

Hope that this helps.

Chas.