How to Change a Square Taper Bottom Bracket

The bottom bracket is a key element to a bicycle, whether it be road, mountain, cyclocross or BMX. This piece of equipment connects the two crank arms together and connects on the bottom portion of the frame between the front and rear wheel. Square-taper bottom brackets are found on older bicycles and can be classified as either ISO (most European-made bottom brackets) or JIS (Asian-made bottom brackets). With frequent cycling, the bottom bracket needs replacing after four or five years and it's best to do it yourself to save money and connect yourself with the bike that you ride and love.

Things You'll Need

  • Crank puller
  • Bottom bracket tool
  • 32-mm headset wrench
  • Releasing solvent
  • Rubber mallet
  • Clean, dry shop rags
  • Waterproof lubricant
  • Teflon tape
  • Square-taper bottom bracket (new)
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Instructions

    • 1

      Align your crank puller with the outer bolt on your cranks and insert until snug. With a few cranks on the lockring, or left-hand, side, your crank will loosen and remove in either one piece or separate pieces, depending on the type of crank you're using.

    • 2

      Insert the bottom-bracket tool on the lockring side and, with the 32-mm headset wrench and the bike lying on its side, turn the wrench counter-clockwise, while keeping the lockring secure with your free hand. If the wrench doesn't turn easily, have someone tap gently on the bottom-bracket tool with a rubber hammer or spray some solvent on the lockring to loosen the bottom bracket.

    • 3

      Remove the loosened lockring and flip the bicycle over to the other side and insert the bottom-bracket tool. Using the 32-mm wrench, turning it clockwise, remove the entire bottom bracket.

    • 4

      Wipe the interior of the bottom bracket shell with your clean dry rag and lubricate the interior portion with a light layer of waterproof lubricant. Apply Teflon tape to the threads on the bottom bracket threads and thread in the lockring, making certain to leave it slightly loose.

    • 5

      Flip the bike back over to the other side and insert the new bottom bracket. Screw it in by hand until it's tight and tighten the lockring with the wrench and bottom bracket tool. Reattach the cranks, making certain they spin freely with no wiggle or deviation from a circular motion.