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I have had a terrible time trying to remove crank arms from the square taper spindle. The tool used correctly just was forced out and stripped the threads. The left-hand side was about half off and I managed with some cutting to get it off. The drive side with hammering and cutting and even drilling so far has not yet been removed. On closer inspection inside the interface after some cutting, it seems that the two metals steel spindle and aluminium crank arms have almost been bonded together. What causes such a thing to occur???

Is it dry mounting? overtightening with pneumatics? I have noticed this is a feature on decathlon bikes as even removing the crank arm screws was very difficult and involved power tools. Is this a common flaw of the square taper system or is it an incorrect mounting procedure by the manufacturer? If I am to attempt to stick with this system and replace the crankset do I use anti seize mounting paste in future or grease or abandon such system for the external bottom bracket ie hollowtech.

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    Could be any or all of your ideas as a cause. Lack of assembly lube might contribute to galling as well. Once you get the cranks off the BB, clean it and do a very close inspection. With bright light and a straight edge or a razor blade. Replacement of the BB and cranks might be your best option if there is damage.
    – Criggie ♦
    Commented Mar 18, 2021 at 9:23
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    ill post a pic but the left side spindle just shows some dark gray discolouration,other Than that is physically intact.right hand one still not got it off will do some more drilling this evening.
    – elpocketo
    Commented Mar 18, 2021 at 11:07
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    @Criggie you may be aware of this, but Campagnolo had long advised mechanics to not grease the tapers at all. That advice was later shown to be wrong, but the practice might have persisted. Anyway, dark grey discoloration might suggest galvanic corrosion between the aluminum of the arm and the steel spindle. renehersecycles.com/to-grease-or-not-to-grease
    – Weiwen Ng
    Commented Mar 18, 2021 at 12:44
  • Be happy you have this problem and not the much more common opposite ;) Have you tried heating up the aluminium crankarms? It does sound like galvanic corrosion, use grease or maybe Loctite 648 (retaining compound) in the future.
    – Michael
    Commented Mar 18, 2021 at 13:22
  • ive managed after couple of hours drilling around the spindle to get it off.but seems like the bottom bracket is a write off as sounds and feels very crunchy indeed,perhaps all the oil and wd40 i was using whilst drilling possibly got inside it.might have to take the new hollowtech like bb and cranks to bike shop or ill have to dish out for more tools to get this bb off.
    – elpocketo
    Commented Mar 18, 2021 at 18:18

2 Answers 2

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You just need to use a thin layer of grease to prevent bonding between steel and aluminum. Also if you’re having great difficulty when removing the crank arms, spray some liquid wrench in there and wait. Make sure that the puller is fully screwed onto the external crank arm threads to avoid stripping as opposed to partially screwing them on. Finally, remember that force over time means that applying less force over a greater period of time is equivalent and often greater than a large amount of force applied all at once I.e. strong arming. What that means is that you can set up some tension on the puller and leave it, and just keep applying a little more tension if it still won’t budge. Almost like magic, it will give way eventually.

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  • As the OP suggests, liquid wrench, WD40, etc sprayed around that area are likely to get inside the square taper BB bearings and dilute/wash out the grease there, requiring a new BB. The BB's are normally quite inexpensive but it's something to keep in mind. Also, I strongly second making sure the crank puller is fully screwed in.
    – Armand
    Commented Mar 23, 2021 at 3:11
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thanks for the comments folks.I decided to replace it with a hollowtech type bb which has been a joy to put on and use so far.I wont be going back to square taper.I managed to get the existing square taper bb off without too much hassle.In future i know if i go on a long ride and any issues with bb or cranks i only need allen key,small tool for preload nut and small tool for hollowtech splines,no more pain of crankpullers and cutting crank arms off for days.How do i close this thread now?

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