How to Remove a Threadless Headset
Below are instructions for removing a threadless headset. This is the most common type of headset today, found on almost all modern road and mountain bikes. (It is called the "threadless" headset because there are no threads on the fork's steerer tube.)
Step 1: Remove fork and stem.
This job will be easiest if you unhook your cables and remove your stem and fork. Also remove all the parts of the headset, including the bearings. You'll be left with two headset cups in the frame and a crown race on the fork.
Step 2: Get an RT-1 Race Tool (from Park Tool.)
We will be using this specialty tool from Park to remove the headset cups. Start by sticking the tool up through the head tube, narrow end first. As the wide end enters the frame, squeeze the sides in so it can enter the headtube and then expand again. It should line up with the headset cup and make a clicking sound when it locks into position.
Now use a hammer to tap the narrow end of the tool. Keep tapping until the lower headset cup falls out of the frame.
Step 3: Repeat.
Now repeat Step 2, but reverse the process so you remove the upper headset cup.
Step 4: Remove crown race from fork.
The last thing to remove is the crown race, which sits on the fork. There is a tool made for this called the Park CRP-1, but I use the old fashioned method.
The old fashioned method involves a hammer and a big flatblade screwdriver. You line up the flatblade under the crown race and then tap it with a hammer. Work your way around the entire circumference of the crown race, taking care not to scratch your fork. The crown race should loosen and slide off.
Note: You can wrap a rag around the screwdriver to help prevent damage to your fork or crown race.
Caution: If you have a carbon fiber or other expensive fork, be very careful when removing the crown race!
Step 5: Clean up.
Take a rag and wipe down the headtube and fork steerer tube to clean off any old grease or dirt. You can also take the opportunity to inspect your headtube area for stress fractures.