Crank Replacement - standard - Ultimate Guide to Mountain Biking in Utah

Crank Removal and Replacement

The crankarms can be damaged where they attach to the spindle of the bottom bracket, or where the pedal threads at the distant end. In that case, you're going to need to get the correct replacement set before you start. Or, you may just need to remove the chainring-side crank to replace chainrings. We'll cover 3 types of crank attachment:
     Female-threaded tapered spindle - the most common type, where a bolt holds the crank on the spindle.
     Male-threaded tapered spindle - where a nut holds the crank onto the spindle.
     Splined spindle - where the spindle is a ring with teeth that fit into slots in the crank.

Damage at the spindle (where the square hole in the crankarm fits over the square dohickey sticking out of the bottom of your bike) is usually due a loose retaining bolt. The crank arm slips a bit away, making the connection loose. The spindle rotates a bit in the mounting hole and gradually deforms it. Damage at the pedal end of the crankarm occurs when crappy metal meets up with a heavy biker slamming down on the pedal.

If you're replacing a damaged crankset, you need to buy a correct a replacement crankset. Some cranksets (for example, those designed for eliptical chainwheels) bolt onto the chainring itself. Most attach directly to the spindle -- the freely-rotating thing that sticks out from the bottom bracket.

If your bike has a crank attachment other than the standard female-threaded tapered spindle, you'll want to jump to another page that covers these alternate crank attachments.
     Male-threaded tapered spindle - where a nut holds the crank onto the spindle.
     Splined tapered spindle - often found with hollow bottom brackets, spindle has tapered teeth, requires crank-puller.
     Other crank attachments - go to the manufacturer's web page, or do a web search

Female-threaded tapered spindle - the most common type, where a hex-head bolt holds the crank on the spindle, which is square with rounded edges, and has a threaded hole drilled into it.

Pulling the crank off can be an adventure, especially on a cheap bike.

Pulling the crank off can be an adventure, especially on a cheap older bike.

If there's a plastic protector cap, pry it off. Now remove the retaining bolt. On most mountain bikes, this is a hex-head bolt. (On some bargain-basement bikes, the spindle may end in a threaded bolt, with a nut holding the crank onto the spindle. If that's what you've got, you're on the wrong page. Click here !)

If you loosen the bolt, then the crank falls away to show a ring with teeth, you have a splined crank: click here !

Remove the bolt from the spindle. If the crank attachment is damaged, the crank may just fall off the spindle. In most cases, you'll need a crank extractor tool.

DON'T remove the crank by pounding it or prying with a lever. You'll destroy the bearings in the bottom bracket!

Removing the retaining bolt from the spindle.

Part number one of a crank extractor.

See the treads around the inside of the crank? Thread the big end of the crank extractor into them, as far as it will go.

Now turn the core of the crank extractor in until it stops.

Part number two, the core.

As you twist, the extractor pulls the crank away from the spindle.

When the core stops turning easily, it has hit the spindle. Now it's time to apply a wrench to the core. (Most crank extractors come with a handle specifically for that purpose.)

Continue turning until the crank has come loose from the spindle.

Inspect the spindle for damage, and check for side-to-side (left-to-right) motion of the spindle in the bottom bracket.

Listen for grinding or rubbing as you turn the spindle. If the bottom bracket is bad, now's a good time to replace it .

Checking the bottom bracket spindle.

Removing the chain-side crank, plus chainrings.

To remove the chain-side crank, put the chain around the frame at the bottom bracket. (Note: the big disk is a "tooth fairy" protecting the large chainring from damage.)

Now use your hex wrench and crank extractor exactly as you did on the other side. The crank will come off with chainrings attached.

To remove the chainrings from the crank, unscrew the locking. If you don't have a lockring tool, you can take off the small chainring and remove the ring with a large pipe wrench.

If you removed the crank to replace chainrings (rather than replacing a damaged crankset), go to work on that now.

Ready to take the rings away from the crank, if needed.

Now place the new crank -- in the same position on the spindle as the old one. Apply Loctite to the threads of the retaining bolt. Tighten the bolt, and (if you have one) replace the protector cap.

You're now ready to thread the pedal into the crankarm.