Never seen this before
03-25-22, 01:18 PM
#1
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Never seen this before
Fixed cup on BB split on me. Had been in there for years, w/no issues. Used the Sheldon Brown technique to remove
03-25-22, 03:28 PM
#2
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03-25-22, 04:10 PM
#3
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What do the threads in the BB look like? Any chance it was cross-threaded and started breaking long ago when tightened to the BB face?
03-25-22, 06:17 PM
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I’ve seen a lot of those but only from Helmart Slagnesium bikes.
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Stuart Black
Plan Epsilon Around Lake Michigan in the era of Covid
Old School…When It Wasn’t Ancient bikepacking
Gold Fever Three days of dirt in Colorado
Pokin' around the Poconos A cold ride around Lake Erie
Dinosaurs in Colorado A mountain bike guide to the Purgatory Canyon dinosaur trackway
Solo Without Pie. The search for pie in the Midwest.
Picking the Scablands. Washington and Oregon, 2005. Pie and spiders on the Columbia River!
03-25-22, 06:59 PM
#5
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They're fine. I popped in a replacement no problem
03-25-22, 07:00 PM
#6
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It was on an old Apollo steel frame road bike
03-25-22, 09:20 PM
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Agreed, the bearing track becomes work hardened (likely from overly preloaded bearing adjustment) and in time cracks. The tough ones are when the threaded skirt completely breaks off the flange and remains stuck in the shell. Andy
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03-26-22, 04:10 PM
#9
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I’m guessing that somewhere along the line, someone either didn’t know (or forgot 
) that the fixed cup was “left hand threaded” and applied way too much counter-clockwise force in an attempt to remove the fixed cup. The threaded portion kept moving toward the center of the bottom bracket shell and split away from the outer portion of the fixed cup. I’ll agree that with a quality fixed cup this would be unlikely but with a cheaply made, poor quality or even rusted component, it’s not beyond the realm of possibility.
) that the fixed cup was “left hand threaded” and applied way too much counter-clockwise force in an attempt to remove the fixed cup. The threaded portion kept moving toward the center of the bottom bracket shell and split away from the outer portion of the fixed cup. I’ll agree that with a quality fixed cup this would be unlikely but with a cheaply made, poor quality or even rusted component, it’s not beyond the realm of possibility.
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04-02-22, 06:39 PM
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I’m guessing that somewhere along the line, someone either didn’t know (or forgot ) that the fixed cup was “left hand threaded” and applied way too much counter-clockwise force in an attempt to remove the fixed cup. The threaded portion kept moving toward the center of the bottom bracket shell and split away from the outer portion of the fixed cup. I’ll agree that with a quality fixed cup this would be unlikely but with a cheaply made, poor quality or even rusted component, it’s not beyond the realm of possibility.
) that the fixed cup was “left hand threaded” and applied way too much counter-clockwise force in an attempt to remove the fixed cup. The threaded portion kept moving toward the center of the bottom bracket shell and split away from the outer portion of the fixed cup. I’ll agree that with a quality fixed cup this would be unlikely but with a cheaply made, poor quality or even rusted component, it’s not beyond the realm of possibility.The reason why this happens as I have understood it is the ball track inside the cup suffers erosion, massive wear and both is thinned out (right at a stress focal point of a corner in the shape and the change of thickness as the threads stop a little bit before the flange and I suspect work hardened by the balls. Thus the thinned and brittle spot can crack. Andy
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04-02-22, 07:18 PM
#12
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Not a bad theory> IME I have never had this happen (the cup's end wall/flange breaking off during removal) unless the cup was already cracking (and then only a few left their threaded skirt inside the shell). This includes many fixed cups that I needed impact tools and/or lever arms a few feet long.
The reason why this happens as I have understood it is the ball track inside the cup suffers erosion, massive wear and both is thinned out (right at a stress focal point of a corner in the shape and the change of thickness as the threads stop a little bit before the flange and I suspect work hardened by the balls. Thus the thinned and brittle spot can crack. Andy
The reason why this happens as I have understood it is the ball track inside the cup suffers erosion, massive wear and both is thinned out (right at a stress focal point of a corner in the shape and the change of thickness as the threads stop a little bit before the flange and I suspect work hardened by the balls. Thus the thinned and brittle spot can crack. Andy
04-02-22, 07:48 PM
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Next time you have a fixed cup with a similar crack please section it about the crack to show the fracture face. If it's clean and "bright" your theory is likely correct as there would have been no crack during use to dirty or leak old grimy lube out of. Then I will certainly believe your theory. And will post her saying so.
However the photo shows what looks to be ground metal filings which would agree with my suggestion of a very work ball track (I used the word "erosion"). Andy
However the photo shows what looks to be ground metal filings which would agree with my suggestion of a very work ball track (I used the word "erosion"). Andy
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