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Old 06-27-06, 02:23 PM   #1
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Bottom bracket type

I intend to replace an old bottom bracket, but having no expertise in bicycle mechanics I can't quite figure out what type it is. The bracket has a 127.5mm spindle, is possibly made by Shimano, installed in the early nineties. Both cups have a regular splined inner edge; the left side cup is metal, with a lip that is flush with the outer surface of the BB shell, and bearings can be seen within by removing a rubber seal ring. There are threads at the inner visible end of the spindle on the left side, terminating in a cylinder with a rounded slightly hexagonal shape too deep to access with a spanner. The right side cup is plastic, and has no notable features. I suppose that's the "adjustable" end.

Neither end of the BB really looks like the few pictures I've seen of cup-and-cone brackets, but the bareable bearings don't fit what I know of cartridge brackets. Furthermore, from what I read the adjustable cup is usually on the left side, not the right as it is here. I've got a replacement cartridge BB waiting in which the sides appear to be reversed and the bearings completely inaccessible.

Is this a cup-and-cone or cartridge BB? Did someone install it the wrong way around or are bottom brackets with the adjustable cup on the right commonplace? I tried preliminarily opening both sides after a WD-40 soak, spline tool fastened with a long bolt and turning in the direction of pedalling on both sides, but the rings wouldn't budge.
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Old 06-27-06, 03:02 PM   #2
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I'm not certain but I'm pretty sure you have one of Shimano's very low line cartridge bottom brackets. I recall seeing something similar a few years ago.

Remove the cartridge (metal) end first. The plastic ring is likely to break if you attempt to unthread it first and you will have a hard time removing the left-over pieces. Trust me on this.

Bottom brackets, if installed correctly, are very tight and may require extraordinary force to get them loose. Be sure you are turning them the right way and use a BIG wrench.
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