The crankset is one of the main components of the bicycle drive chain and it’s used to transfer motion of the rider’s legs into a rotational motion. The motion used to drive the chain then turns the rear wheel. In the centre of the crankset is a set of bearings that will ensure the crank arms run in a smooth rotation, when the bike is being pedalled.
Over time the bearings will wear out as they grind against each other, making it harder for the crank to turn. Before the crank bearings are changed, it’s important that you understand the types of bottom brackets available and how to remove and replace the crank bearings.
THE DIFFERENT TYPES OF BOTTOM BRACKETS
The crank bearings are part of the bottom bracket assembly that slots into the round bottom bracket shell on the bicycle frame. This part will contain the spindle that is the axle of the crankset; this part allows the bearings to move smoothly. The crank bearings are connected via spindles with one being attached on the surface and one onto the frame.
There are a number of different bottom bracket configurations. Older bicycles tend to have something known as a cup and cone bracket. Whereas many new bicycles, use cartridge bottom brackets.
Types of Bottom Brackets
Loose Bearings - Three piece assembly with separate spindle and cranks
Cartridge - Sealed units holding the bearings and the spindle
One Piece - Spindle and crank arms are a single piece with bearings pressed into the bottom bracket shell
Pressed Bearings - Bottom bracket with bearings pressed directly into the bicycle frame
REMOVING THE CRANK BEARINGS
Changing bicycle crank bearings is quite a simple process and it involves removing the old unit and inserting a new one. Removing crank bearing assemblies will require special tools such as bottom bracket tools or crank pullers. Cup and cone assemblies will usually require a long ring spanner and pin spanner.
Replacing the cartridge crank bearing will begin by removing the crank arms. Next use the bottom bracket tools to unscrew the old unit. Modern bicycle bearing use a reverse thread on the bottom bracket and will involve unscrewing it in a clockwise direction.
Cup and Cone Removal
When removing a cup and cone assembly you will need to begin by removing the lock ring with a specialist spanner; this will free the cup for removal. Then you should use the pin spanner or a chisel and mallet to unscrew the cup. Once the cup is removed , you can take out the bearings.
At this stage it’s important to take note of the way the bearings retainer comes out. The new bearings should be put in the same way. The cup on the right side of the bracket should be left on the bottom bracket; leaving this part will eliminate any accidental damage being caused.
Preparing The Bottom Bracket
Before installing a new crank bearing and reassembling the bike, the bottom bracket should be thoroughly cleaned. Use a specialist solvent degreaser to degrease the congealed grease and remove any grit. When doing this make sure the threads are in good condition.