The cranks of a bicycle must be properly maintained for the bicycle to function well. These are the bars or levers connected to the bottom bracket through a spindle (usually a square at the ends). If you need to change the cranks, you can do it as long as you have the right tools. First, you will need to separate the pedals from the cranks. You will then need to use an Allen wrench to remove the center bolt from the crank before replacing it. You can use this process to replace Shimano's two-piece cranks, SRAM's self-extracting two-piece, and three-piece cranks.
Part 1 of 3: Detaching the Pedals
Step 1. Separate the right pedal from the crank arm with a 15mm wrench
The crank arm is the elongated piece that connects the pedals to the crank. Place the wrench around the bar that connects the crank arm and the pedal. Then, turn the wrench counterclockwise 2-3 times to release it from the crank arm.
When the pedal is loosened, it should turn freely on the crank bolt
Step 2. Rotate the crank arm clockwise to release the pedal
Hold the pedal and turn the crank arm clockwise. Keep turning it until the pedal disengages from the crank.
- You should be able to feel the pedal unscrewing from the crank arm as you turn it.
- It may take 10 to 30 full turns of the crank to get the pedal out.
Step 3. Repeat the process on the left pedal
The left pedal is reverse threaded. Use a 15mm wrench to loosen the left pedal of the bike. Next, hold the left pedal and rotate the crank arm to fully separate it from the bike. After this, the two pedals should be completely separated.
- If you stand on the right side, or the drive side, turn the crank arm clockwise. If you stand on the left side (or the side without the transmission), turn the crank arm counterclockwise.
- Set the pedals aside in a safe place so you can put them back once you finish replacing the cranks.
Part 2 of 3: Remove the crank
Step 1. Remove the cap from the center of the connecting rod, if equipped
Some cranks have a metal or plastic cap that fits over the bolt. If your crank has one, place a screwdriver under the edge of the cap to remove it. This will reveal the connecting rod bolt.
The crank bolt will be in the center of the crank and it will look like a hexagon
Step 2. Loosen the set screws with an Allen wrench, if the crank has them
Some cranks have set screws or two smaller screws, near the top of the arm. If your crank has them, insert a 5mm Allen wrench into the holes in the upper arm and turn the wrench counterclockwise.
- Loosening the clamping bolts will allow you to remove the crank arm from the rest of the chainrings.
- The 2 bolt design is from Shimano cranks. For these types of cranks, you will also need to remove the plastic preload bolt on the left side (the side without the drivetrain) of the bike.
- Not all cranks have these set screws. If your bike crank doesn't have them, skip this step.
Step 3. Place an Allen wrench on the connecting rod bolt and turn it counterclockwise
Turn the crank on the Allen wrench counterclockwise to loosen the crank bolt. Then use it to fully unscrew the screw.
- If the crank has bolts on both sides of the bike, go to the other side and remove the other bolt.
- Most cranks require a 4-8mm Allen key. Check your bike's instruction manual or manufacturer's website to find out which size will fit your bike.
- Allen keys are also known as hex keys. You can find them at your local bike and hardware stores.
Step 4. Slide the crank off the spindle if you have self-extracting cranks
Pull the crank arm to separate it from the bottom bracket. Then, slide the other side of the crank out of the chainrings. Pull the rest of the crank to remove it from the bottom bracket.
- If there are rubber washers around the spindle, remove them before installing the new connecting rods.
- You don't need a crank puller tool for self-extracting cranks.
- You will know if you have a self-extracting crank if it only has one bolt on one side of the bike with a retaining ring around it.
Step 5. Loosen the cranks with a crank puller if they are not self-extracting
Purchase a crank puller at a bike store or online. Insert the crank puller into the crank bolt hole and turn clockwise to screw in until tight. Then, turn the puller handle counterclockwise until the crank releases. Go to the other side of the bike and remove the other side in the same way.
Crank pullers are required for models that are not self-extracting. These types of cranks have a bolt on each side of the bike and do not have a retaining ring around the bolt
Part 3 of 3: Install the new cranks and reinstall the pedals
Step 1. Put the right crank on the spindle at the 6 o'clock position
If you have washers, put them around the spindle before installing the connecting rod. Push the right side of the crank over the right spindle and loop the chain around the chainring so that it is between the bike and the crank.
Position the chain so that it goes from the rear gears to the chainring
Step 2. Slide the left crank over the spindle at the 12 o'clock position
Move the left crank arm and push it to the end of the spindle. If either side of the connecting rod does not reach the end of the spindle, use a rubber mallet to push it into place.
Step 3. Screw the new connecting rod bolt into place using an Allen wrench
Put the crank bolts back in place. Then screw them in with the same Allen wrench that you used to uninstall the old cranks. Turn each screw clockwise until you can't go any further.
Step 4. Replace the protective cap and tighten the retaining screws, if necessary
If the crank bolt has a plastic compression cap that goes over it, place it over the center of the bolt and press it down to snap into place. Tighten the cap to the recommended torque setting, which is typically 5 Newton meters. If the crank has set screws, turn them clockwise with a 5mm Allen wrench to tighten them and secure the crank to the bike. Tighten them according to the manufacturer's specifications, which is usually about 15 Newton meters.
Self-extracting cranks do not have set screws
Step 5. Screw the pedals onto the crank arms
Put a pedal in place and start turning the crank counterclockwise. This is an easy way to screw the pedal back onto the bike. Go to the other side of the bike and repeat the process. Continue threading the pedals onto the crank arm until they are tight.
- Most pedals have a marking that says "R" and "L" for right and left respectively. This will help you determine which pedal goes on which side.
- Make sure that the threads on the pedals match the grooves on the crank arm so that the threading is not damaged.
- Damaging the threads of both the puller and crank arm is common, especially on gears and older bikes. Take precautions before beginning the extraction, including heating the arm with a heat gun, cleaning and drying the threads of the puller and arm with alcohol or a similar chemical, making sure that the puller is fully inserted (screwed in) before begin to force the components, carefully insert 3 or more shims behind the arm or gears before starting the separation.
- When you start to start the puller, pay close attention to the threading. This should take no more than one or two turns of the crank to free. If you see a gap in the thread, even minimal, stop. You may need to take other steps to loosen the crank (such as riding the bike without the bolt) before trying again.
- If the connecting rod threads are worn, try cutting it with an emery board. The crank arm is not repairable anyway. Do not hit it if you can avoid it, as it may cause damage or misalignment to the crankset bearings or other parts. Be careful to avoid hitting the spindles during this step, as this can affect the installation of the replacement crank arm.