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I broke my bottom bracket axle a few days ago, and when I removed the crankarms I discovered my old bike is using a cup and cone bottom bracket but more importantly the bracket shell is a bit odd. It is not threaded, the left cup is stuck or glued to it and goes all the way until the right side of the shell. On the right side it is threaded and allows the right cup to be screwed in it. I have included a few pics.

First pic is the left side of the shell, the broken axle is still there, you can see an hexagonal piece that screws around the left cup to secure it to the shell I guess, although the left cup is already firmly glued to the shell and doesn't really move.

Second pic is the left cup naked. You can see a little space between the shell and the cup all around it. And how it goes all the way until the right side of the shell.

Third pic is the right side of the shell. The left cup seems more firmly attached to the shell on this side. There seems to be some glue between the cup and the shell. The inside of the cup is threaded to allow for screwing the right cup.

enter image description here enter image description here enter image description here

Have you ever seen that kind of system? Is it safe? I was planning to clean the cup, clean the bearings (maybe throw some new ones), grease and replace the bearings, put a new axle, close and seal everything, and finally screw the crank arms. Is this the correct procedure to replace this kind of bottom bracket?

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    Can you, please, measure the B.B. shell width and diameter? Also providing the make and year of the bicycle can give us some clue on what it can be. You can also refer to Sheldon Brown's bottom bracket crib sheet: sheldonbrown.com/cribsheet-unthreaded-bottombrackets.html – Mike Jun 17 '18 at 10:58
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    Thanks. I've googled and came across someone else with similar problem: bikeradar.com/forums/viewtopic.php?t=12592913 - there is a cross-section of this bottom bracket. Looks to me like a French invention. I wouldn't try to remove the "fixed" cup. Just like you said - clean everything, find a new axle and assemble it back again. If you remove the whole set you end up with a threadless BB frame and those are said to be not worth to be brought back to life. – Mike Jun 17 '18 at 12:37
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    @Mike - you should put that as an answer. Depending on what the threadless BB frame is like, you can use threadless BB's like the velo orange grand cru one. – Batman Jun 17 '18 at 13:34
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    You certainly should replace the bearing balls while you're replacing the shaft. – Daniel R Hicks Jun 17 '18 at 13:54
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    What's the inner the diameter of BB shell? Maybe you can thread it to accept something more conventional? – Klaster_1 Jun 18 '18 at 5:34
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I'll put some thoughts that appeared in the comments:

I've googled and came across someone else with similar problem: bikeradar.com/forums/viewtopic.php?t=12592913 - there is a cross-section of this bottom bracket:
French MBK bottom bracket from https://www.bikeradar.com/forums/viewtopic.php?t=12592913
Looks to me like a French invention.

I wouldn't try to remove the "fixed" cup. Just like you said - clean everything, find a new axle and assemble it back again. If you remove the whole set you end up with a threadless BB frame and those are said to be not worth to be brought back to life.

Suggestion of Batman:

Depending on what the threadless BB frame is like, you can use threadless BB's like the velo orange grand cru one

which I agree to, however the price tag on Velo Orange bottom brackets is hefty. It may be worth if the frame has substantial value either financially or emotionally to you.

From my own experience - I have a bicycle with high emotional value which has Thompson BB (pressed in cups). The BB shell is 42mm in diameter. Velo Orange has a solution for that however it exceeded my budget. I was lucky enough to find a press-in Thompson/Thun replacement of sealed bearings cartridge with a square-taper spindle (the original was cottered, hence the idea of replacing it).

In the meantime I came with an idea for you. Since it is a road bike, perhaps it would be possible to upgrade the BB to, let's say, Hollowtech? You'd have to measure the inside diameter of the BB shell (dark blue in the cross-section, labelled as Frame) and check if press-in Hollowtech bearing cups exist, maybe some adapter shells will be necessary.

Another idea is, if you want to stay with some vintage yet standard stuff is to press in a complete BSC threaded shell:
enter image description here
This one I've found here: http://www.wiggle.nl/sram-pressfit-30-naar-bsa-adapter/ - seems quite "generic" and available in more countries.

Then, when having BSC threads you can simply put sealed bearings cartridge with square-taper spindle and enjoy the maintenance-free bottom bracket.

But again - my choice would be to find a new spindle (since you already have a square taper) if the spindle is of standard measurement, replace the bearings and assemble it back again - there is only one cup and cone to adjust and, as I can see in your pictures, there are the lip seals on the BB spindle making the whole package quite sealed, thus maintenance-free.

  • The BB30 to BSA adapter requires a BB30 compatible frame, something much larger than what OP has. – ojs Jun 17 '18 at 18:01

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