bOTtOm BrAcKeTs

Bottom Brackets

(It makes the bicycle go vroom!)

Bottom brackets are an essential part of the bike. Without them you would not be able to pedal. It is sandwiched in between the crank arms in the part of the bicycle called the bottom bracket cage. The bottom bracket is merely a spindle that rides on two sets of bearings and races, one on each side. The spindle sticks out on both sides and connects to the crank arms and then the pedals. There are three basic types: sealed cartridge, adjustable, one-piece.

• • A sealed cartridge means the bearings and axel are encased and only one cup is loose. This protects the bearings and is much more durable than an adjustable or one piece bottom bracket.
  • An adjustable bottom bracket consists of all the pieces separate. This style is very serviceable and is what is most commonly found in the Green Bike Shop.
  • A one piece bottom bracket is simply one piece that is the axel and both crank arms. This can be slightly serviceable as long as the races on the axel are not worn. If they are, the entire piece must be replaced.

Problems that arise with the bottom bracket are few; most of the time it is a worn or loose bottom bracket. A worn bottom bracket usually means the bearings are becoming crushed and/or the races are wearing in. This leads to further deterioration until the bearings are cracked and the bottom bracket seizes. A loose bottom bracket could lead to crushed bearings and/or the crank arms to come off.

Assessing whether or not the bottom bracket has one of these problems is simple. Take the chain off the crank set and spin the crank arms. If you feel a grinding vibration or hear grinding coming from within the bike, this probably means the bottom bracket is worn. A loose bottom bracket can be easily detected by grabbing both crank arms near the pedal and torque both arms towards and away from the bicycle. If you feel play when doing this it could be that either the bottom bracket is loose or the crank set itself is loose.

In order to service the bottom bracket:

• • Place a rag to the side. This is where you will put the parts you take off the bike in order so as to help with reinstallation.
  • Take off both crank arms by loosening the crank bolts and removing the crank arms with a crank puller.
  • If the bottom bracket is loose, tighten the loose cup(s)/lock ring one eighth of an inch at a time. After each eighth check to make sure the spindle is still loose.
  • If the bottom bracket is worn, remove the loose cup/lock ring and carefully place the bearings aside.
    • Next remove the axel.
    • If the bottom bracket is a sealed cartridge bottom bracket by removing the fixed cup the bottom bracket should come out.
    • Finally remove the opposite cup and bearings.
    • If the bottom bracket is a sealed cartridge it cannot be serviced and must, sadly, be thrown away.
    • If it is an adjustable style, clean and examine the axel, both cups, and the bearings. If any is worn replace it.
    • Reinstall all parts opposite the way they were taken out; making sure to grease both sides of the bottom bracket.