Replacing the crank on a bicycle

Sometimes the crankset needs to be replaced. Sometimes the teeth wear out, and replacing just the chainring is uneconomical. Less common is damage to the crank arm itself or the threads. Sometimes the crankset needs to be removed for service or simply for cleaning. Regardless of your reason for doing so, the goal is clear. This short guide will show you how to replace a bicycle crankset step by step. I'll cover replacing the most popular square and spline cranksets, as they're the most complicated to service. Finally, I'll devote a short section to typical old wedge-lock cranksets and modern models with integrated axles. In the meantime, enjoy!

How to replace a crank on a bicycle?

Let's start with the most important tool . You need a crank puller. In an emergency, you can do without one (I know from experience), but it's not worth it. A simple task can turn into a struggle, and it's very easy to damage the crank and bottom bracket. The puller is designed for a specific standard, so make sure you buy the right one. You'll also need a wrench to remove the pedals (a 15-inch flat wrench or a 6- or 8-inch hexagonal wrench). For the crankset bolt, a 14-inch socket or a 8-inch hexagonal wrench is needed (most standard ones won't fit). Depending on the puller model, you'll also need two more wrenches – usually regular open-end wrenches in sizes 14 to 18.

Replacing the crank on a bicycle - let's get started

First, we need to clear the area foreground by unscrewing the pedals, remembering that the left pedal has a left-hand thread, while the right one has a standard thread. The entire process is described in detail in this article . Removing the pedals from the removed crankset can be quite a challenge. Next, unscrew the screw securing the crankset to the axle. This screw is often hidden under a plastic cover. It always has a small notch that allows you to easily pry it out. A small screwdriver is ideal for this purpose. The screws on both sides are standard, right-hand thread—no surprises there.

You'll see that the hole in the crank is also threaded. This is where you should screw the puller in. Before doing so, make sure the threads are clean and the inner part of the puller isn't screwed in so tightly that it rests on the axle. Replacing the crank is all about precision in simple steps. Screw the puller in as far as it will go and tighten it gently – there's no need to force it. Then, screw in the inner pin with your fingers until you feel resistance, then use the wrench to push the crank off the axle. This will require considerable force – I recommend standing the bike firmly on the ground. You might even need to use a hammer on the wrench. After a few turns (this may take a while), the crank should come off the axle. Simply unscrew the puller and repeat the process on the other side!

How to install a bicycle crank?

Easier than removing it :) First, clean the bottom bracket with degreaser if you're not replacing it. Just be careful not to get it on the bearings, as it can easily wash out the grease. It's important to apply a little grease to the crank shaft before installing it. It prevents seizing, and a seized crank will end up in a mess. Place the crank on the shaft and tighten it (also with a greased bolt). Apply a generous amount of force – about 40 Nm. In practice, you should ease off when you feel everything is securely seated, and moving the wrench a small distance requires jerking and bouncing. Simply tighten the pedals (lubricating the threads) and you're done!

Replacing the crank with a wedge or integrated axle

The wedge-type cranks found on older bikes aren't the best solution – they tend to pick up play. Replacing them is as simple as it is brutal. Simply unscrew the nut at the end of the wedge, then use... two hammers. Place the first under the crank on the wider side of the wedge, and then use the second to hammer it with all your might. Expect to damage the wedge, so it's a good idea to get a new one right away. Install it the other way around – hammering in the wedge, then securing it with a washer and nut.

For models with an integrated axle, it's best to check the specific manual on the manufacturer's website. Most, however, operate similarly. First, loosen the two opposing screws that clamp the left arm to the axle. Then, unscrew the large, central screw, and the arm can be removed. Sometimes, the clamping screws also have a small safety latch – simply pry it out slightly with a small screwdriver.

This time, it's more complicated the other way around. First, tighten the central bolt to eliminate any play, but still allow the crank to rotate smoothly. Then, alternately tighten the arm compression bolts – again, be careful with the force. It's easy to strip the thread or damage the bolt, so it's best to use a torque wrench. With cranks secured with a single central bolt, there's probably nothing to explain :)