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Replacing BB shell on a French frame?

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Replacing BB shell on a French frame?

Old 02-17-23, 08:42 AM
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Replacing BB shell on a French frame?

With out getting into the fever dream of why, how would I go about replacing the bottom bracket shell of a French frame that has French tubes? I assume the problem would be under sized tubes in a standard lugged shell. I'm just trying to get an idea if its actually feasible. Thanks
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Old 02-17-23, 10:15 AM
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I think the bigger issue will be dealing with 4 tubes at the same time and keeping all in alignment. BB shell replacement is a repair that you don't hear much about for, IMO, the reason that it is more involved than simple tube or dropout replacements and there are alternatives to damaged threads (the most common reason to have to deal with a shell) that don't involve a torch and frame repairing skills.

But to try to offer an answer of method one could reduce the shell sockets IDs with brazing in shims and opening the sockets up to the amount needed before the shell is placed in the frame. Seems to me to be a lot of work.

Which begs the question, why replace the shell? Are the threads buggered up? Is the shell cracked or otherwise structurally damaged? If the goal is to end up with a BB availability improvement (from French to ISO threading) I suggest considering a Phil BB instead with their French retaining rings. The Phil BB should last a very long time, it will be rebuildable (just sent one back to Phil for new bearings, came back nice again), is transferable to another bike (with the proper rings) and doesn't do anything to the frame. A reversable repair is usually my first consideration. Reaching for my torch is generally the last method I would do. Andy
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Old 02-17-23, 12:34 PM
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I'm with Andy on the approach I would take, get a bb and forget about replacing the shell. There are a couple of solutions depending on what is wrong with the frame now.

I replaced an Italian bb shell with an English bb shell just to say I did it. It's not really that bad. To do this on a French frame, you could blacksmith the spigots of the shell to make them fit better. Shells are pretty ductile and I don't think it would be too hard to close down the openings.
De-brazing a bb shell in one piece is going to be pretty impossible unless you have a hearth. I just cut the shell into pieces and then de-brazed the pieces.

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Old 02-17-23, 04:53 PM
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I replaced an Italian thread shell that cracked around the seat tube socket with an English thread shell and have been riding it as my commuting bike for over 30 years now:

But it was a big job; I don't think it would be feasible unless you're able to do the labor yourself. And sourcing a metric-spec shell could be a chore in itself.

Originally Posted by Andrew R Stewart
Which begs the question, why replace the shell? Are the threads buggered up? Is the shell cracked or otherwise structurally damaged? If the goal is to end up with a BB availability improvement (from French to ISO threading) I suggest considering a Phil BB instead with their French retaining rings. The Phil BB should last a very long time, it will be rebuildable (just sent one back to Phil for new bearings, came back nice again), is transferable to another bike (with the proper rings) and doesn't do anything to the frame. A reversable repair is usually my first consideration. Reaching for my torch is generally the last method I would do. Andy
If the shell is still structurally intact,that's a better idea. Another option would be to ream the shell and tap fresh Italian threads to use a standard Italian thread bottom bracket. Bicycle Research used to sell a reamer/tap set for exactly that purpose:
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Old 02-17-23, 07:07 PM
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I have some French-diameter shells, not sure if I'm willing to sell one. Inquire if interested and I'll find out if I need all the ones I have. I will need to inventory my metric-diameter 753 tube sets and compare to the number of shells I have. I will sell if I have more shells than tubes. These are Cinelli investment cast, best you could get back then (late-'70s, early-'80s)

The way I have replaced a shell involves removing the old shell by sawing it into pieces that can be melted off one at a time. Fitting the new shell is challenging, like a Chinese puzzle box, but with patient persistence you will wiggle it on.

Still, I would much rather make heroic efforts to save the existing shell.

If the problem is the thread: I have the reamer to go from French to Italian, and also (optionally) threaded inserts that make an Italian shell into English. The right-side insert is even left-hand threaded on the inside, RH thread on the outside (how do they do it?) I guess in theory you could make those inserts to fit French threads too, but I have never seen them for sale. Those inserts can be just threaded in cold, so you could repair a frame without disturbing the paint.

Another option I've done is the cut'n'weld: saw through the bottom of the shell, then hammer the saw kerf closed, weld or braze, and chase the threads. If the original thread is especially buggered, you might gang up 2 or 3 hacksaw blades to get a wider kerf, to reduce the shell's circumference by more. I like brazing the saw cut because then you have some braze inside the shell, which is more material for cutting new threads — I puddle some extra braze down there, inside, if there's a lot of steel missing (stripped threads). The braze or weld can be done so fast that it doesn't even burn the paint on the top of the shell where it shows, so for customers who didn't care much about looks, we'd do this repair in like 10 minutes out the door, plus however long it takes to remove and re-install the crankset.

Another option, never had to do it but I've thought about it, is bore out the old shell (probably with a 1-1/2" precision holesaw, or maybe a boring head?), then silver-braze in a 1-1/2" (38 mm) lugless shell. Requires a milling machine, and a somewhat complex setup, so this would not be a quick repair suitable for a cheap frame. The original shell is probably ~40 mm so you'd theoretically have about 1 mm wall thickness remaining on the old shell, and a huge amount of wetted area for the braze. So with even partial braze penetration, you should have a shell that's plenty strong when done. I envision doing this on a high-dollar frame like a '50s Singer that had its shell completely squashed somehow, like dropped from a height with no cups in the shell.

Next step up from that would be to use a 40 mm holesaw so the entire horizontal "tube" of the original shell is gone, and then fillet-braze a new shell to the DT, ST and C-stays. That's assuming the sockets in the original shell aren't what broke.

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Old 02-17-23, 07:58 PM
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Its the "blacksmithing" part that I cant visualize. I'd approach like choking a gun barrel, maybe adapt a pipe cutter by "replacing" the blade with another roller and insert a mandrel in the lug socket?

As to the "reason"....I was trying to figure out how to convert a tandem to a single seater. I'm picking up a second light weight french tandem for the parts, and I do not have high hopes for rehomeing the frames. These are simple frames with no extra tubes or struts and 1" stearers, and I am solidly in the clydesdale camp.

P.S. I just got a better picture of tandem #2 and its lugless, so thats a different kettle of fish....

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Old 02-18-23, 07:53 AM
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"And they all moved away from me on the bench there, with the hairy eyeball"
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Old 02-18-23, 09:37 AM
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"and creating a nuisance" and we all came back.

If anything a filleted shell should be a bit easier to remove. But I'm still unsure to the need to replace the shell. Do keep us in the loop and post a follow up. Andy
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Old 02-18-23, 02:01 PM
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[QUOTE=bark_eater;22804259]"And they all moved away from me on the bench there

Originally Posted by Andrew R Stewart
"and creating a nuisance" and we all came back.

If anything a filleted shell should be a bit easier to remove. But I'm still unsure to the need to replace the shell. Do keep us in the loop and post a follow up. Andy

​​​At this point I'm primarily trying to rationalize keeping a few tandem frames around as future projects, verses scraping them. The potential fillet brazed frame, I will have to determine its intrinsic "Value" before cutting into it.

​​Sticking with the lugged Gitane in my garage, I cant remember off hand which BB shell is split for the eccentric bottom bracket, or how that actually works. I dont think there are threads. Assuming its the rear BB shell the front shell will not have sockets for chainstays, just a horizontal "bottom tube". So destructive removal and replacement seems in order.
I probably would also need to replace the seat lug, and I guess the seat tube, so reassembly, shouldent be to deep.

This is of course coming from an armchair frame builder, and Im sure there's a a lot that i dont know that I dont know...

​​​​​​Like how to adapt imperial lugs to metric tubes....
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Old 02-18-23, 02:02 PM
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Originally Posted by Andrew R Stewart
"and creating a nuisance" and we all came back.

If anything a filleted shell should be a bit easier to remove. But I'm still unsure to the need to replace the shell. Do keep us in the loop and post a follow up. Andy

​​​At this point I'm primarily trying to rationalize keeping a few tandem frames around as future projects, verses scraping them. The potential fillet brazed frame, I will have to determine its intrinsic "Value" before cutting into it.

​​Sticking with the lugged Gitane in my garage, I cant remember off hand which BB shell is split for the eccentric bottom bracket, or how that actually works. I dont think there are threads. Assuming its the rear BB shell the front shell will not have sockets for chainstays, just a horizontal "bottom tube". So destructive removal and replacement seems in order.
I probably would also need to replace the seat lug, and I guess the seat tube, so reassembly, shouldent be to deep.

This is of course coming from an armchair frame builder, and Im sure there's a a lot that i dont know that I dont know...

​​​​​​Like how to adapt imperial lugs to metric tubes....
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Old 02-18-23, 02:50 PM
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When I said "blacksmithing" I meant beating on the spigot with a hammer. Probably want to have the appropriate sized tube around to check sizes. I do this all the time when I bend the stay sockets out for s-bend stays. Some people do this shaping when it's on the tube, but I always figured I would hit the tube or the lug itself might deform the tube. I often use blocks of wood or a dowel to get the blows exactly where I want them.

I don't know if you have built a frame. I find repairs to be much less satisfying than building, and it's a bit more difficult. The results never come out as good as I would like. I guess it's nice to bring something back from uselessness. But tandems make good cargo bikes.
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Old 02-25-23, 01:45 PM
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Quick up date on the madness. The French fillet brazed bike doesn't look like a good candidate because the the 2 bottom bracket shells are different diameters. other frame related trivia is that its "bent". The 2 seat posts are not parallel and there is paint cracking at the there the top tube(s) connection with the captains seat-post. If any one here is interested in a free French tandem frame with alignment issues, let me know.

P.S. I went for a walk and decided that the 2 different BB diameters, isnt insurmountable, but the frame being a size too small is.




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Need help identifying French 650b tandem

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Old 02-25-23, 10:32 PM
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That looks like it might be Reynolds tandem tubing from the '70s. Oversized top tubes and the shaped bottom tube suggest that.
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Old 02-26-23, 04:21 AM
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Originally Posted by unterhausen
That looks like it might be Reynolds tandem tubing from the '70s. Oversized top tubes and the shaped bottom tube suggest that.
Shop I worked at (R+E Cycles) used to sell those, in about '79-'80, ordered right from France. We got them in bare steel, customized them a little sometimes (braze-ons) but mostly just painted and decaled them as Rodriguez. No deception; we made it clear these were Follis-built. It was a bike we could sell right away, when we had a multi-YEAR waiting list for the USA custom frames.

I think we actually got them through Lejeune, but don't trust my memory on that. I wasn't involved in that part of the biz, I only made the "real" Rodriguez tandems, the custom made-in-USA ones. TBH I tried as much as I could to ignore that side of the business. I was an artiste and a snob... and 23 years old, gimme a break. Also, Angél Rodriguez didn't like me, he actually fired me, then his partner Glenn Erickson hired me back a few minutes later. After which me 'n' Angél didn't talk. For the next five years I worked there. In his defense, I was a terrible employee.

Anyway, from seeing the Follis/Lejeune tandems naked I can tell you for sure (OK mostly sure?) they were not Reynolds. Also, we ordered a box of their forkblades to use in our custom forks but we found them substandard, not nearly as nice as the 531 "Jack Taylor" tandem blades that fit the same OS crown sockets... with some massaging. The Lejeune blades (wherever they got them from, not saying they made steel tubes there) were a primitive "football" shape, not the sophisticated elliptical shape of a Reynolds blade, so both the blade and the crown needed some persuading to make them fit. Also the Lejeune blades were not taper-gauge, so they thickened up substantially at the bottom end. I think they were slightly thinner at the top than the 531 JT blades also, despite bing thicker at the bottom. Not terrible — I like these French tandem forks a lot — but they're not as excellent as real 531. Which were a lot more expensive as you'd expect. I think the real JT blades might not have cost more really, after you figure the labor cost of fettling blades and crowns to fit, using those French blades. The 531 oval fit perfectly with no fettling, unsurprising since they were what the crown was cast to fit.

About the oval bottom tube: it was a 1-1/2" round tube, that then got squashed, same as Reynolds. Not hard to make. Ishiwata also had their version, pretty indistinguishable from Reynolds, which is what Santana used. Later for my customs, when I was free to design them however I liked (at Davidson), I went to larger but thinner-wall bottom tubes, so I consider 1-1/2" to be kinda wimpy by today's standards. But it's what most everyone used back then, either that or the same tube, left unsquished (round), as with Schwinn Paramount.

The Follis/Lejeune tandems were slightly oversized throughout, per the standards of the day, though we'd call that tubing small for a tandem these days. If I recall, the front downtube was 30 mm (probably plain gauge), which isn't even what we'd call "single OS" on a single bike in the modern era. Y'know, where "single OS" is a 1-1/4" (31.7 mm) DT and double-OS is a 1-3/8" DT. Jack Taylor, Rene Herse and others used the 30 mm 531 DB tandem downtube. Seems skinny nowadays but at the time it was cutting-edge. I used that 30 mm 531 DT on my first MTB in '81, thought I was so sly...

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Old 02-26-23, 08:03 AM
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Thanks for the history lesson. I always found it interesting that the industry was stuck with "standard" size tubes for everything but tandems. R&E should have slapped a diagonal tube in there.
I also was an anti-French snob at that time, but in my defense the first nice French frame I saw was my track bike in 1980. And I'm not convinced it's really French. It's still a mystery. The only decal it ever had on it was a reynolds sticker.
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Old 02-26-23, 02:32 PM
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Originally Posted by unterhausen
Thanks for the history lesson. I always found it interesting that the industry was stuck with "standard" size tubes for everything but tandems. R&E should have slapped a diagonal tube in there.
I also was an anti-French snob at that time, but in my defense the first nice French frame I saw was my track bike in 1980. And I'm not convinced it's really French. It's still a mystery. The only decal it ever had on it was a reynolds sticker.
Freddy Parr has more or less claimed to have invented OS*, says he made OS race frames in the '70s. Maybe early '70s? I forget what he claimed. Said they were the secret weopon of some good SoCal trackies and crit guys. I don't remember hearing of those from anyone else besides Freddy though.
.028" plain gauge probably would have been the thinnest he could get, so these were probably not light.

Santana's 1-1/4" DB from Ishiwata might have been the first DB tube in 1-1/4", anyone know of anything earlier? They first got them in '77. Not sure if they ordered them from the Ishiwata catalog, or if they were first made at Santana's request. I'd bet money Santana's ridiculously oversized forks and chainstays were specially made for them; no way Ishi just had those tubes in their catalog. Raking the forks took a cheater bar about ten feet long and I'm not exaggerating. It was still difficult and we would have made the bar longer, but it had to clear the ceiling before the bend started and finish before the bar hit the floor. I thought they looked like cricket bats. Stiff! They still used a 1" steerer though, an extreme lack of vision IMHO. Especially since they already sold Jack Taylors that came with an OS steerer (28 mm). OS steerer was a bridge too far for them? Later of course they went all the way to 1-1/4", the size almost no one used, so stems were close to nonexistent.

* well there were a few weirdos like the Schulz which had about a 2" downtube, in the late 1930s I think? Or the Paris Galibier (UK-built despite the name) of the late-'40s with about 1-1/2" DT (from vague memory, don't quote me on that). Someone once showed me a tandem from the 1890s with all 1-3/8" tubes, and it was impressively light, so very thinwall OS tubing was available over a hundred years ago.

But this is the FB forum not C&V, sorry for the musty dusty history.
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