Thank you.

No, we are talking about the fixed cup on the right side. The threads of the adjustable cup on the left are right-handed which means they screw in in the opposite direction from the rotating stress. Thus they will screw themselves in.

French BBs use right-handed threads on the fixed cup side too, which means they screw in in the same direction as the rotating stress. Thus they will screw themselves out.

Yup. Swiss bottom brackets on the other have a left sided threading. This makes life interesting if you need to turn it with a wrench and don't know which way to turn.

hmmmm, all somewhat counter intuitive but I think I'm getting it , with the help of your interesting illustration. Thanks for posting that.
Scott

I also have an old French bike that will probably be upgraded from cottered to cotterless sometime in the future. To summarize the early info in the thread: You can use your old cups and just get a new spindle but the new spindle must have the same measurements between the races, etc. Or you can replace it as a whole unit and all you have to worry about is that the replacement is French threaded. The French threads are lefty loosy tighty righty on both sides. So watch which way you turn. It is better to leave the fixed cup in there unless you are replacing it.

Is that right so far? If you are replacing the whole unit how do you determine what size of spindle goes in? I was going to put the cottered cranks/chainrings on the old spindle, take a measurement from there and convert to cotterless. I am going to use a Stronglight 93 cotterless crankset. My cottered spindle is 137mm with 56mm between the races. Does anyone know what that would be in cotterless?

In years of riding French bikes, I have never had a fixed cup come loose. I install them with the Var 30 tool, which allows you to torque them down real good-like. I'm aware it can happpen, that seems to help stop the problem before it develops. I have never used loctitie on a fixed cup.

Interestingly, I've repaired several fixed gears in recent years that had the English thread fixed cup come loose. Same basic problem, I think: the back-pedaling and resistance stops work the fixed cup loose on English-thread bikes. I've tightened them up as well with the Var tools, no further problems reported. The most recent was brought to me by a co-worker at the art center I teach at, a local shop had quoted her 75$ on the job (I did it for free).

Seypat, most older Stronglight doubles used a 120, IIRC. However, be aware that the Stronglight spindles have a different taper than that of the current, JIS (Japanese Industrial Standard) taper used on the VO BB, amoung others.

Basically, the distance between races can be broken down into two categories: thin walled (more distance between races) and thick walled (less distance between races). Older French cups tend to be thin walled. New cups (80s on) tend to be thick walled. The old Stronglight cups were thin walled.

There is handly info on spindle tapers in older editions of Sutherland's Handbook for Bicycle Mechanics.

I had one come loose once. It was decades ago before I realized the possibility. A bike shop fixed it and explained the problem. I think you are right that knowing about it makes it not happen. It must be some sort of quantum mechanics thing.

I had one fixed cup come loose on my Gitane. I hand tightened it several times on my way back to my starting point. Later I cleaned the threads with solvent and used Loctite on the threads. So far, so good.

I'm not sure about your explanation. In normal operation the cup doesn't rotate in the shell. Your circle-in-circle description doesn't explain where the force comes from that makes a right-threaded fixed cup want to break loose from its grip on the threads of the shell and start turning.

There may not be any rolling friction between spindle and bearings, or between bearings and cup, but there is thrust, from the "grip" between the moving parts. (If there was no grip, the balls would not roll when the spindle rotated in contact with them. The spindle would just slide over them. But because balls on polished steel have such low rolling friction, very small amounts of thrust will make them turn.) And it's that thrust that makes pedaling action want to turn the cup: the spindle turns the balls, and the balls (try to) turn the cup.

Think of the steel wheels of a train locomotive resting on a steel rail: very low rolling friction -- what there is comes from the slight deformation of the rail and the wheel at their point of contact by the weight of the locomotive. But when the engineer applies power, the wheels thrust against the rail and start the train moving. (If there was no grip, the wheels would just spin.) Where heavy trains climb steep grades, such as from Field, B.C., up to the Continental Divide at Stephen, this thrust against the rails causes them to creep downhill perceptibly enough to be a track maintenance issue, despite all those thousands of spikes holding them down to the ties.

You can demonstrate this "bearing precession" effect at home: Take two cups, some dry balls (no grease), and a spindle. Assemble the parts as if they were going into a bike but hold the spindle vertically so that one cup floats freely on the "top" race of the spindle as if it were a hat. Now, holding the lower cup with one hand to keep things steady, contrive to spin the spindle with a variable-speed electric drill. At a very low speed, the top balls will stay "stuck" to spindle and cup so the top cup rotates the same direction as the spindle. As you spin the spindle faster, so that your thrust becomes enough to start moving the balls, the floating cup starts to lag behind the spindle, then stops, then begins to move ever faster in the opposite direction.

Q.E.D.

You're right, I didn't explain that. The "rotation" is actually a rotating radial stress. The pedal loading pushes on the back and bottom of the cup, and the opposite pedal induces the same stress through the rest of the pedal cycle. In other words, there is an outward force on the cup wall, and that force moves around in a circle. It does not apply a significant circumferential force, but rather a radial force. The cup simply rolls around the inside of the shell. (Note, it is not required that the force be the same through the entire pedal cycle. It is required merely that it rotate.)

If friction from the spindle transmitted to the cup through the bearings was the reason for the cup moving it would tighten a right-handed thread on the right side of the bike. It doesn't do that.

I believe that all of the Old French doubles used a 118. They seem to be plentiful. I see them all the time on Ebay.

The above may very well be correct. It's been awhile since I actually measured a spindle on an old SL crank, and I'm going on a memory extremely faulty on exactitude. I do know that the SL cranks took substantially longer BB spindles than modern cranks. 118 sounds about right, but so did 120.

I do recall one questioner who came here looking for a SL spindle length. He was building a fixie, and the fixie kids had told him to get some ridiculously short spindle length. We told him different, but he decided the fixie kids knew more. His crankarms wound up hitting his rear stays. Score one for C&V.

Isn't there a special tool for putting those in and getting them properly torqued..... As for examining the cup, get a good bright flashlight and once you have cleaned everything good with a rag and solvent, shine the light in there from the adjustable cup side and have a look, maybe use a light with a magnifier so you can see it better. Mind you if I were taking out a fixed cup, I would likely put in a cartridge BB, so it would not be as big an issue, since they use the same tool for both sides.

I wonder if the Velo Orange thread-less ones will work on a Raleigh threaded bike, which has a 76mm wide shell????

From their website:
You may have to be the guy to try it and find out on the 76mm shell. If it doesn't work, you can sell the BB at a small loss and consider that the price for the knowledge.

It's not friction. It's thrust. There is a difference which you are confusing. In this case, the difference causes the cup to turn in the observed direction which is opposite to the direction it would turn if it was friction.

Use a compression fit Mavic BB. Good enough for winning classics, and the Tour de France (stages and GC) back in the day. Any uber bike shop should have a set of Mavic BB chamfering tools collecting dust in the closet. After chamfering your shell, the Mavic BB fits via compression.

The BB doesn't care what the shell "was" (french, english, italian).

You'll get a silky smooth BB, and an epic BB.

A Mavic BB is a useful component to use on vintage frames with destroyed BB shells, or with french BBs. Keep it in your idea toolbox.