Bottom Bracket Threading Mystery
 

I have this French race bike 70s-80s that has a french threaded BB that I am building for a friend. I took off the BB to see some artifacting that makes me think it was retapped or modified some point in the past. Are these small thread lines in the middle of the BB shell common?
https://cimg2.ibsrv.net/gimg/bikefor...32023a30f.jpeg

CDFJ wrote:
I have this French race bike 70s-80s that has a french threaded BB that I am building for a friend. I took off the BB to see some artifacting that makes me think it was retapped or modified some point in the past.
Are these small thread lines in the middle of the BB shell common?

The French BB has all right hand threads; they passed one threading tool through the whole bracket.
At some spot there seemed to be more wall t hickness and that left the marks.

Greetz, Wiel

Would it be at all possible that they changed the threading from BSE or ITA when they did this or is that completely impossible? I would think yes but I feel I should ask since I'm still trying to identify the frame as well and this could shed light away from it being more difinitively french if that's the case.

When you make a frame the BB is usually supplied with some threads in it. But after welding (or brazing) you "chase" them with a tap because there's often a bit of distortion from the heat. It looks pretty likely that the original shell was tapped all the way through in a single operation as Wiel said. Then after brazing the builder probably chased only enough on each side to put the cups in, going in from each side one after the other rather than running a tap the whole way though.

I don't think you could retap from ITA to French as the tap size is smaller for French. Maybe you could go from BSA to French. But if you were you probably wouldn't cut the whole way through like that.

It's highly doubtful that a factory would go to the trouble changing an existing shell's thread spec, especially when it's vastly easier to just go with a different BB when the bike was assembled. Wiel has got this right. Those marks in the shell's central section are artifacts of a tap being run all the way through.

A further indication that this frame saw as little manufacturing cost as possible is the lack of the tubes having been mitered to any real extent. Andy

Gotcha okay thank you for helping me clear up that it's likely all on the manufacturing side rather than done aftermarket by the consumer at a later date to either change or update the threading. When you say that the lack of mitering indicating a lower manufacturing cost, would this indicate a larger production bike typically or something done by a smaller maker? Like I was saying above I'm still trying to identify the frame and will probably strip the paint to see if there are markings that are hidden by the heavy powdercoat done by a previous owner. Here is a picture of the full bike for reference
https://cimg4.ibsrv.net/gimg/bikefor...d12a98692.jpeg
https://cimg5.ibsrv.net/gimg/bikefor...30b6c79a8.jpeg

That's an interesting frame, and likely it was modified later given all the braze-ons. There haven't been a lot of production bikes that used that seat stay/seat lug attachment method, too much work for most factories. Those dropouts aren't particularly old though. The domed stays/fork argue against any modifications there, I think. I'll admit to being confused.

It's common enough, but I don't think every bb manufacturer ran the taps all the way through French and Italian bb's. I think most machines are made to come in from both sides, even though the taps would be the same.

Zullini Machine 2 Jpeg | Powered BB chasing and facing with … | Flickr

Link to a Flicker photo of a lathe like production tool for threading, facing and reaming steel frames. Var, IIRC, had tools with much the same function. Andy

I would not try any stripping of the Powder Coating because there is nothing under it. To Powder Coat, it needs a bead blasting which removes any old paint from the frame. You are at the mercy of the frame guru's here on the forum for identification. Smiles, MH

I don't think that "bracket tappen" machine could go all the way through. It has a support on the opposite side.

Threadcutters come in more styles and forms. VAR169 is a reamer/ threadcutter that goes all the way through the bottombracket. French can be changed to Italian (35 to 36mm) not the other way .

Greetz, Wiel
https://cimg9.ibsrv.net/gimg/bikefor...1d89114dbc.jpg
A tool for cutting threads by VAR one pass in Italian or French threads.

The lack of mitering tube ends is more the method of larger high volume producers where saving 5 minutes per joint would really add up to a huge time savings after a few thousand frames. For a small short run or singular frame shop that savings has less value and could cost some reputation.

Perhaps the best known example of the savings that a well engineered joint (and joining process) can have is Trek. When they were still making their frames here in the US they began to use a one piece headtube and lugs form. A sheet of steel is stamped/cut, pierced and, wrapped then welded. Tange offered this part, among others. The head tube's "lug" were stamped relief, only the top and down tubes actually entered a socket. Those tubes were left square cut. Not only time savings from no mitering but also had less brazing filler in a far simpler joint to flow. Now add preheating stations on the frame brazing carousel and the time to flow the joint comes down to only a few minutes each joint. Andy

Andy a small correction. I think these one piece lugs were made by the Nikko company. They are bulge formed. They start life as one piece of tubing and are shaped under enormous hydraulic pressure. We used these on the 1st transportation bicycles we made in Ukraine because Kostya our original builder could make them easier and faster that way. I got those one piece lugs from Miele when they went bust. I still have a bunch.

Trek silver brazed Nikko lugs when they started making frames in the 70's. I got a supply of Nikko blank and spearpoint lugs for my students a few years ago. They are really nicely made. Their angles can be more easily changed than investment cast lugs. And they are nicer than the old stamped and welded lugs because they have no seams.

Doug is correct and since I have a Nikko catalog on my desk I should have remembered it. That the head/lug piece was bulge formed is new to me. Thanks for the correction. Andy

Oh I'm loving all this info on the frame parts it's given me so much insight! I did end up starting stripping the paint because I was getting antsy and an (affordable) sandblaster was over an hour away. Y'all were right that nothing is under the paint to discover which doesn't surprise anyone. I did see someone mention tange and I found this bike on ebay recently that used tange steel as well that I thought had many similarities. Then I suppose where I go from here is, is this frame a mass produced undranded, or possibly something built by someone on their own?

https://www.ebay.com/itm/33432951827...YAAOSw3xViClSY

I doubt it was a homebuilt. I think it's likely it was modified later, probably when it got recoated

Are there manufacturers that build frames that are completely unbranded, maybe as a base for people to modify? that might be very stupid because that doesn't exist.

My 1988 Schwinn Prelude was built in a similar fashion with square cut tubes. I can even see the remnants of small rectangular pieces of brazing filler that were placed inside some of the joints and then flowed out, presumably in some sort of hearth or multi flame brazing fixture.

CFDJ- The close up of the "Schrade" frame's dropouts suggests a lot to me. The fork's, actually the complete fork, look like a production Tange one. Likely not made by the same place that did the frame. The rears show poor finishing aesthetics with the chain stay ends not really matching the seat stay ends. IME a sign of at least small batch building by a production crew (and far from a single builder's usual attention to more than mere joining efficiency).

As to frame factories making frames for others to modify, I seriously doubt that. Now contract building is a classic way for someone to become a frame "maker" without the skills or factory set up. This is a lot of what we see with all those secondary/third tier "brands" that sell on line. But the off shore contracted factory will generally finish, paint, decal the frames and ship them to the, also off shore, assembler (which can mean to the other end of the same building) for the build up with parts and boxing. \

There have been (and might still be...) "brands" which have off shore frame suppliers but do enough finishing (the paint and decals) to be able to claim "domestic" making (although these import, added value here rules are evolving). Two examples in widely different sectors of the bike industry are: Raleigh (of America) imported their (un painted) Technium frames and did the rest in WA state and were able to reduce tariffs and claim "USA". Ten Speed Drive (of FL back in the later 1980s) would import (mostly all, IIRC) Italian made frames and also did the remaining finishing state side. In this case I believe that was more about quality control and stocking ease (paint didn't need to be done till they knew what colors were selling faster). Their "brands" were classic Italian ones that wouldn't benefit from any USA contribution. Still a business model that worked for their needs for a number of years.

This "house labeling" is much of what we see at the local grocery store so this should be of little surprise. In the bike world the "house label" is the bike brand that has decided it can't afford to own the factories. Andy

plenty of contract builders out there. TSD in the U.S. used to paint their Italian bikes because Italian paint was usually about as durable as the coating on Chicklets gum. I have a bike with a Netherlands based bike shop house brand on it that has the engraving for the Italian company that made it for them. Well, it did before I removed the bb shell and the rear triangle. I think when I was at Trek in the '70s that tange was trying to get them to buy frames, and they did later on. You could get them however you wanted, painted, unpainted, etc. These are available by the container load, I doubt any of them made it out to the public for sale as an unbranded bike.

But I think it's clear your frame has been repainted, and thus the branding has been removed. The C&V folks would probably be better at figuring out what it is for you.

No, you can't go from Italian to French, Swiss, or English. Not without some kind of insert, anyway. But going from French, Swiss, or English to Italian is possible.

Yes, until the mid-80s most of the 4nn, 5nn, and 6nn series frames used one-piece, bulge-formed head tubes from Nikko. Starting in the mid-80s, they used one-piece cast head tubes from Signicast in Milwaukee. These can be distinguished by a "TREK" cast into the head tube "lug."

I did find some more markings after stripping the paint if that helps ring any bells!
https://cimg3.ibsrv.net/gimg/bikefor...be4ed0f4e.jpeg
https://cimg4.ibsrv.net/gimg/bikefor...fc2747134.jpeg
https://cimg5.ibsrv.net/gimg/bikefor...0d0340284.jpeg

BCM is Bocoma lugs. 73 is the angle the lug was initially made at. A rather common brand that many companies used. Andy

Interesting aside and sorry to bring the modern world into this but I think this does happen now with carbon fibre frames and forks. There are companies in China who will sell you standard frames and forks. All you have to do is add a brand. This is why traditional brands like Cannondale change hands for more than they ever have but have never meant less.