Home » Bike Maintenance » Removing and refitting chainsets

Removing and refitting chainsets

Why do you need to remove your chainset? There are several reasons. Either to fit a new one, to fit a new bottom bracket, to tighten your current bottom bracket in the frame, to fit new chainrings or to clean properly behind the chainset.

Removing chainsets and cranks – square taper, ISIS and Octalink

  • Remove both crank bolts. Most cranks are bolted on with an 8mm Allen key. Crank bolts must be snugly fitted, so you need a long Allen key for fitting and removal – use one that is at least 200mm (8 inches) long, otherwise you won’t be able to free the bolt or refit it properly at the end. Both crank bolts have conventional threads that undo anticlockwise. Check inside the crank recess for any washers and remove them.
  • Look into the hole that the bolt came out of. It’s either an older square taper or a newer splined taper, which will look like a notched circle. If you have an older crank extractor designed for square taper axles and a splined taper you need a special plug to pop into the end of the axle, so that the crank extractor doesn’t simply disappear down inside the axle without pushing it out. Shimano makes one: a tl-fc15.
  • The crank extractor consists of two parts, one threaded inside the other. The outer part bolts onto the threads in the crank, the inner part then gets wound in, pushing the axle out of the crank. Before you fit the tool onto the crank, wind the inner part out so that it disappears inside the body of the tool. Hold the body of the tool
    steady with one wrench and wind the shaft anticlockwise.
  • Clean the threads inside the crank and grease them. They are cut into the soft alloy of the crank and it’s very easy to accidentally strip them with the harder threads of the crank extractor, an expensive mistake to remedy. Start the crank extractor in the crank threads by hand, then tighten with a spanner. Don’t go mad.
  • Wind in the extractor shaft using a spanner. It turns quite easily until the shaft touches the end of the axle, then gets harder as it starts to push the axle out of the chainset. Once it’s moving through the crank, it should slide off easily. It helps to brace the crank against the spanner so they are parallel. Keep your arms straight and use your shoulder muscles. On the chainring side, keep your knuckles well away from the chainrings – the spanner
    gives suddenly, and skinned knuckles are common.
  • Once you’ve got the cranks off, look at them. Left-hand cranks are particularly prone to damage where they fit onto the bottom bracket axle. The thread is a normal right-hand thread, so if the crank gets loose, your pedalling tends to loosen it, until every pedal stroke deforms the mating surface between the crank and the bottom bracket axle. Square taper cranks are more prone to this, but both need to be checked carefully. If the square taper or splines are damaged, the crank or chainset must be replaced – the taper splines will continue to work loose and will eventually damage the matching surface of your bottom bracket.

Removing and refitting chainsets

Refitting chainsets and cranks – square taper, ISIS and Octalink

  • Refitting is much easier than removing – the crank bolt acts as a refitting tool, so you won’t need the crank extractor. Clean the ends of the axle and the hole in the crank or chainset. Some people like to grease the taper or splines, but this can make the cranks creak as you pedal so you might want to leave them dry. Titanium axles are the only exception to this – they need to be generously coated with Ti-prep or copperslip.
  • Slide the chainset onto the axle. Grease the threads of the crank bolt and grease under the head of the bolt. The crank bolts for splined bottom brackets use a fatter bolt with a separate washer, which needs a bit of grease on both sides. Older, 14mm spannertype bolts have an integral washer. Fit the crank bolt and tighten firmly. You will not be able to get enough leverage with a standard length Allen key – use one with a handle that’s at least 200mm (8 inches) long. Line the left-hand crank up so that it points in the opposite direction – this can be tricky with splined bottom brackets – and refit the crank bolt.
  • Retighten both cranks after your first ride.
  • If you have a torque wrench, this is one of the places where it’s most useful – undertightened cranks will quickly work loose. Recommended torques for crank bolts are generally between 35–50Nm. See page 21 for more information on torque settings.

Removing and refitting chainsets compatible with external bottom brackets

“It’s very easy to accidentally strip them with the harder threads of the crank extractor”

See also bike maintenance tips, tricks and techniques “Refit any bar ends and bar-end plugs”