9. How to Replace Cotterless Crank Arms

Crank removal and installation procedure on a square-spindle, sealed bottom bracket.

IMPORTANT: Nuts and bolts on your bike should always be tightened to the manufacturer's specifications.
How to Replace Cotterless Crank Arms
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  • 02:08 - The crank bolts should be torqued to about 35 foot-pounds, or 420 inch-pounds.

This tutorial will demonstrate how to remove and install square-spindled crank arms. I’ve based this tutorial on cranks attached to a sealed cartridge bottom bracket. I’ll cover the loose-bearing style in a future tutorial.

Tools Required

To remove the bolt, you’ll need either an 8mm allen key or 14mm socket wrench. To remove the crank arms, you’ll need a crank puller, a 16mm open-end wrench, and an adjustable wrench. If possible, a torque wrench should also be used for tightening.

Crank Arm Removal

In order to safely remove the right side, you’ll have to shift the front derailleur onto the smallest chainring, and then carefully remove the chain and rest it on the bottom bracket, so that it doesn’t interfere with the crank arm removal.

Using the crank arm for leverage, loosen and remove the tightening bolt with your allen key or 14mm socket wrench. Be careful not to skin your knuckles on the chainring teeth.

Before using the crank puller, make sure it is fully extended so that the internal driver does not extend past the external threads.

Note: If crank threads are damaged, there are a few solutions at Park Tools.

Carefully thread the external threads of the crank puller clockwise into the crank arm. Avoid cross-threading, which will damage the crank and prevent future removal.

Once the crank puller is fully threaded, place the adjustable wrench on the external flats and turn the internal driver clockwise until it stops. Turn the driver clockwise using a 16mm wrench, until the crank arm pulls free of the spindle. Repeat the same process to remove the left crank arm.

Crank Arm Installation

Before re-installing the cranks wipe both the square spindle and the crank’s spindle fitting to make sure there is no dirt or grease on either surface.

Now slide the right crank’s spindle fitting onto the spindle. Before installing the bolts, grease under the head and along the threads of both bolts. Thread the bolt all the way into the spindle threads and torque the bolt to about 35 foot-pounds, or 420 inch-pounds.

Set the chain back on the chainring and repeat the same installation procedure on the left side, making sure the crank arm is pointing opposite the right side.

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