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Bottom brackets that have plastic retainers have a reputation for being problematic to remove. Often the tool interface on the plastic retaining ring will shear off if the plastic is old or the bottom bracket is stuck (How can I remove the stripped plastic cups of a bottom bracket?). I (everyone?) would like to avoid such a situation if possible.

What steps can one take to improve ones chances of sucessfully removing the plastic retaining rings?

Some ideas:

The plastic rings are typically made from Polyamide, which is resistant to attack by hydrocarbon lubricants. A penetrating oil might work (to the extent that they work anyway).

The plastic rings are made from a thermoplastic so heating is probably a bad idea. Having said that, it should be possible to heat up the bottom bracket shell with a heat gun or similar to around 100 Celcius. This would expand the bottom bracket shell by some fraction and make it easier to remove the retaining ring. Unfortunately the coefficient of thermal expansion of the rings is likely higher than that of steel. Maybe freeze the rings instead?

Maybe it's possible to attach a metal fastener (by pinning perhaps?) to the retaining rings. I expect this is in the realm of fantasy.

EDIT: To clarify, I am asking exclusively about threaded bottom brackets.

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  • Just to be clear, you are specifically talking about threaded bottom bracket retaining cups, not press-fit cups.
    – Argenti Apparatus
    Apr 12, 2019 at 13:11
  • @ArgentiApparatus Yes I am talking about the threaded variety.
    – maxf130
    Apr 12, 2019 at 14:32
  • "Maybe it's possible to attach a metal fastener (by pinning perhaps?) to the retaining rings. I expect this is in the realm of fantasy." The retaining rings simply sheer off. The PA that is exposed to the environment is very brittle. That inside the BB shell is strong. However, not enought material thickness between threads and cartridge to catch and turn it. Especially since it usually requires a lot of torque.
    – gschenk
    Apr 13, 2019 at 0:43
  • @gschenk who's bright idea was it to make a suck a high torque fastener out of plastic anyway and then give it such a hillariously pointless tool interface. I tried (unsuccessfully) to remove one of these bottom brackets before, I do not have a high opinion of this design.
    – maxf130
    Apr 13, 2019 at 8:42
  • @maxf130 FAG did so at least since the 80s. The bearings are usually long lived. Most bikes will never see a bearing removed. What is more, the nylon cups might also work on damaged threads and not very well made bottom bracket shells.
    – gschenk
    Apr 13, 2019 at 22:05

2 Answers 2

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Based on my experience with such cups I suggest a rather robust approach:

  • cut off the external parts of the plastic cups with a hot knife
  • chisel away material from one side to expose the outer edge of the cartridge
  • apply penetrating oil to all areas
  • heat the bottom bracket with a heat gun (bear in mind the heat may damage the frame's paint @Argenti Apparatus)
  • drive out the bottom bracket by whacking the bottom bracket spindle with a mallet

if that doesn't work * remove the bearings and the spindle * uncover the other side of the bottom bracket * drive out the cartridge with an improvised punch (eg steel tube, hex socket) and a press, apply penetrating oil and heat as before

I'm confident I should be able to remove such a bottom bracket in less than two hours now, if I must. I also shall not ever put myself in a situation where this may happen.

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  • I saw your answer to that question and you sharing your experience is much appreciated. I was hoping though to avoid this situation entirely if possible and take steps to make it more likely that the cups will remove without shearing. In your experience, have you ever successfully removed such a bottom bracket without the plastic shearing at the tool interface?
    – maxf130
    Apr 13, 2019 at 8:31
  • I've removed those only twice. The first one was new and came off easily. The second one not. These FAG cartridge bearings have a very good reputation and often last decades with no problems whatsoever. They are often used in Germany. My impression from reading web forums was that they are typically removed destructively though.
    – gschenk
    Apr 13, 2019 at 22:02
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Use of a heat gun is to be avoided. Amongst other things they are used for removing paint. Those things can get much hotter than you think. A hair dryer is safe, but might not be effective.

Very hot water has been used to unstick stuck seat posts. You could try submerging the BB area in a container of hot water, although that will melt the grease in the bearings.

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  • I have no intention of reinstalling such a bottom bracket so melting the grease is not a concern. The danger of heat guns is a good point however.
    – maxf130
    Apr 12, 2019 at 14:35

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