I have an old 10-speed bike (presumably 80's vintage). I'm trying to remove the bottom bracket and cranks but have struck a problem.

The crank bolts have a plastic cap over the top of them and I'm not sure how to remove it. They look like they should unscrew based on what I could imagine it would look like before they were trashed by the previous owner. I tried to unscrew them gently but they didn't move and as you can see from the photo below they're very fragile.

enter image description here

On the other side the cap has been completely broken. enter image description here

I can see a nut, but with the plastic cap extending into the cavity I can't get a socket in there. I need to remove the plastic somehow.

Anyone have any ideas how to remove the cap and it's remnants?

3 Answers 3


Normally, the cap just unscrews. Obviously, that's not the case here. Use something like the tip of a knife, a small screwdriver or a chisel to break it up and pry it out. But try not to mess up the threads too bad, you'll need them for the next step.

I think what you have is a square-taper crank design; the bottom bracket spindle has a square-shaped tip, the crank is wedged onto that tip and secured in place with the nut. Once the nut is off, you'll need a crank puller. It's a cheap tool, you can get one at any bike shop. The puller has a sleeve that threads into the crank (into the same threads that the cap attaches to); then you screw down a bolt inside the sleeve that pushes against the spindle, and hopefully pops the crank off. This looks like an old bike, so it might be stuck on there pretty good.

When reassembling, just put the crank back on and tighten the nut. Make sure you put plenty of grease on the mating surfaces.

  • 1
    ... when you are at the bike shop also ask for some replacement caps, if not on display they should have a selection out in the workshop. Incidentally, to grease-or-not is a controversial topic: ridemonkey.com/forums/f5/grease-them-tapers-6325 Commented Nov 21, 2011 at 10:41
  • You're right. I got the one in better condition out by putting some multi grips around it and unscrewing. The trouble is the plastic had degraded so much it would just fall apart with any level of force. Thanks!
    – Mac
    Commented Nov 30, 2011 at 3:59

I wonder if they glued the caps in?

Yeah, you'll have to dig out the caps. As you know, they're relatively soft plastic, so it doesn't require super high-tech tools. Probably something like an ice pick to pry a section of the plug body away from the threads, then try to cut through it with a small screwdriver. Or just pry away in several spots and see if that doesn't make it possible to unscrew it.

As Mike said, you need the crank cap threads inside the bolt opening in order to install the crank puller, so try not to damage them very much, and when you install the puller work it in slowly, then back, then in again as you "chase" the (hopefully only) slightly munged threads.

Worst case, if you really wanted to save the bike, you'd have to use an angle grinder with a cutoff wheel to cut away both cranks, or at least cut them back to where you could access the bolts.


Yes. Pop the plastic off with a screwdriver, a lil wd40 won't hurt. Just remember, CRANK ARMS SCREW ON BACKWARDS! left tight,,, right loose,,, also. It may be a european bottom bracket.

  • 1
    What are you talking about? The bolt (or nut, in this case) that holds the crank arm to the spindle? That's not a backwards thread. Commented Nov 22, 2011 at 17:50

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