Changing a pedal crank, or more commonly, a crank arm as part of replacing a bike's crankset, is a maintenance task you can perform with the right tools and technique. It typically involves removing the old arm and fitting a new one securely onto the bike's bottom bracket spindle.
Here's a breakdown of the process, incorporating essential steps for removal and installation.
Tools You'll Need
Before you begin, gather the necessary tools. The specific tools may vary slightly depending on your crankset type (e.g., square taper, Octalink, Hollowtech II), but common items include:
- Pedal Wrench (or a 15mm spanner)
- Hex Keys (Allen wrenches) - various sizes, typically 6mm, 8mm, or 10mm for crank bolts.
- Crank Puller (specific to your crankset type, often square taper or Octalink/ISIS type) - Not needed for some modern cranksets like Hollowtech II.
- Bottom Bracket Tool (specific to your bottom bracket type) - Needed if replacing the entire crankset or certain types.
- Grease - for threads and spindle.
- Torque Wrench - Essential for proper tightening.
Removing the Old Crank Arm
Removing the old crank arm involves a few key steps:
- Remove the Pedal: Use a pedal wrench or 15mm spanner to unscrew the pedal from the crank arm. Remember that the left pedal has a reverse thread, so you turn it clockwise to loosen it. The right pedal has a standard thread, turning counter-clockwise to loosen.
- Access the Crank Bolt: Depending on your crankset, you might need to remove a dust cap first (often with a flathead screwdriver or a specific tool).
- Unscrew the Crank Bolt: Use the appropriate hex key or socket to loosen and remove the bolt holding the crank arm onto the bottom bracket spindle.
- Use a Crank Puller (if needed): For square taper or similar cranksets, thread the crank puller tool into the crank arm. Then, turn the inner part of the crank puller tool to press against the bottom bracket spindle, which will pull the crank arm off its tapered fitting. Modern external bearing cranksets (like Shimano Hollowtech II or SRAM GXP) typically don't require a crank puller; they often have pinch bolts on the non-drive side arm.
Installing the New Crank Arm
Installing the new crank arm requires careful alignment and proper tightening.
- Prepare the Spindle: Clean the bottom bracket spindle and apply a thin layer of grease.
- Align and Fit: Carefully slide the new crank arm onto the bottom bracket spindle. Ensure it is correctly aligned – square taper arms need to be fitted onto the square taper spindle correctly, and splined types need their splines aligned. For cranksets with pinch bolts, fit the arm and potentially a connecting bolt.
- Insert the Bolts: Place the crank bolts (or specific fitting bolts/caps for your crankset type) back into their respective positions.
- Tighten Securely (Using a Torque Wrench): This is a critical step to ensure the crank arm is secure and doesn't come loose while riding, which can cause damage or injury. As highlighted in bike maintenance guidance, like the Halfords UK video snippet on changing a bike crankset[Note: Actual video link not available from snippet alone, generic description used], "Once that's sorted you're good to put the bolts back in right. Now it's time for the torque wrench." Use your hex key or socket to initially snug up the bolts. Then, use a torque wrench set to the manufacturer's specified torque value (this is usually printed on the crank arm, bolt, or found in the manufacturer's instructions). Tighten the bolts incrementally, often alternating between bolts if there's more than one, until the correct torque is reached. Over-tightening can damage the crank arm or spindle; under-tightening can lead to the crank arm loosening while riding.
- Re-install the Pedal: Apply a small amount of grease to the pedal threads and screw the pedal back into the new crank arm. Remember the reverse thread for the left pedal. Tighten the pedals firmly with your pedal wrench.
Quick Reference: Key Steps & Tools
| Step | Action | Key Tool(s) | Notes |
|---|---|---|---|
| Removal | Remove Pedals | Pedal Wrench / 15mm Spanner | Left pedal is reverse thread |
| Remove Crank Bolt | Hex Key / Socket | May need to remove dust cap first | |
| Remove Crank Arm | Crank Puller (if needed) | Or loosen pinch bolts on modern types | |
| Installation | Fit New Crank Arm | - | Align correctly |
| Insert Bolts | - | ||
| Tighten Bolts | Hex Key / Socket & Torque Wrench | Tighten to manufacturer spec using torque wrench | |
| Re-install Pedals | Pedal Wrench / 15mm Spanner | Grease threads |
Changing a pedal crank or crank arm requires patience and the correct tools. Following these steps carefully, especially using a torque wrench during installation, ensures your crankset is safe and properly fitted.
