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Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

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Old 02-17-08, 10:42 AM   #1
SoreFeet
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cartridge bottom brackets/I keep cracking the plastic cup what do I do?

I can't seem to get the plastic cup in without it cracking. Should I worry if it sticks out a little a bit? I can get it threaded in fine but it seems to stick out.

Do I install the metal side first? Or install the plastic cup and them the bottom bracket assembly?
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Old 02-17-08, 10:49 AM   #2
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You are using way too much torque. First be sure the all the threads, BB and plastic cup, are perfectly clean then use grease on all threads. The fixed cup, (drive side) since its metal, needs to go on very tight, but the plastic cup doesn't need that much torque. It should be just snug with about about a 7 inch (3/8) ratchet.
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Old 02-17-08, 11:13 AM   #3
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Quote:
Originally Posted by San Rensho View Post
You are using way too much torque. First be sure the all the threads, BB and plastic cup, are perfectly clean then use grease on all threads. The fixed cup, (drive side) since its metal, needs to go on very tight, but the plastic cup doesn't need that much torque. It should be just snug with about about a 7 inch (3/8) ratchet.
+1

Plastic cups have a torque spec on them. Use a torque wrench.
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Old 02-17-08, 11:18 AM   #4
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Try putting the plastic cup in first, then the cartridge. Grease everything, as above, and also grease the interface between the cup and the cartridge. Sometimes it just won't screw in flush to the BB shell. No biggee.
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Old 02-17-08, 11:39 AM   #5
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I always put the drive side in about halfway then put the plastic cup in halfway. The go ahead and tighten the drive side and then the nds. If you put the fixed cup in and torque to spec and then the nds side you will often get binding which will damage things and break the cup.
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Old 02-17-08, 12:48 PM   #6
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Somewhat related question:

Once it cracks, how do you get it back out? One of my garage sale specials had the plastic cup shatter when I tried to remove it. Not sure how to get the bottom bracket out now.
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Old 02-17-08, 01:47 PM   #7
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If you're doing a retrofit, it's also possible that the BB threads aren't cut cleanly and deep enough. Chase the threads with the thread tap; make sure the plastic cup can go in far enough easily without the cartridge in place. It has to go in far enough to hold the cartridge properly with the correct torque. The amount it sticks out is not an indicator if its not even touching the cartridge.
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Old 02-17-08, 03:07 PM   #8
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You can get the damaged cup out with a couple methods. One of them is to try to crack it the rest of the way off, but the way I would try is to cut it. You have to be careful to make it work though.
Take a Hacksaw blade and cut the cup from the inside out working from the axle hole. You will not want to or be able to cut the whole way through because the threads can be damaged in the frame. Once you get most of the way through, take a large flat-blade screwdriver and a hammer and chip it through the cut or cuts. Once cracked, hit the portions remaining with the screwdriver and hammer and it should crack out the rest of the way. If It doesn't, establish more slot as needed and try to rotate(unscrewing) it.
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Old 02-18-08, 01:32 PM   #9
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Why not just use the cracked cup? It won't seal completely, but since the BB is itself sealed that's not a big deal.
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Old 02-18-08, 01:46 PM   #10
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Here's another tip - clean the threads of the bottom bracket shell with a circular wire brush in a Dremel tool, or a very small circular wire brush in a drill. Clean them out good: get all the rust, dirt, old paint, etc etc. Then apply a lubricant. That helps ease in the plastic cup without breaking it or stripping the threads.
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