Someone recently asked me what to do about an aluminum seat post or quill stem stuck in a steel frame.
First of all, let me explain how this happens.
When two dissimilar metals are placed together, in this case steel and aluminum, and moisture is introduced, ordinary rainwater, a form of electrochemical corrosion takes place known as “Galvanic corrosion.”
The two metals form what is known as an electrical couple, and electrons are exchanged between the two, through the electrolyte, which in this case is the moisture.
The first thing to try to release the two is heat. You could use a butane torch, but a safer and more readily available substitute would be boiling water.
Take the bike outside and lay it on the ground. Leave the saddle or the handlebars in place as you will need these as leverage to start twisting the component to free it.
Pour a pan of boiling water over the aluminum part. If you own an electric kettle this might be a better choice, because you can run an extension cord outside and boil the water right next to where you need it.
Because aluminum expands on heating at a greater rate than steel the seat post or stem is now even tighter than before. However, allow it to cool back to normal temperature, and the aluminum component will shrink. This expanding and contracting again is usually enough to break the seal, and free it.
In the case of a stuck seat post, grasp the saddle and start twisting back and forth. When it starts to move, use a little thin oil or WD40 to avoid tearing up the aluminum.
To remove a stuck handlebar stem, loosen the expander bolt, and tap down the expander wedge to release it, (You must do this.) and then remove the bolt completely before you pour the boiling water over.
As with the seat post, allow to cool completely, hold the front wheel between your knees and start to twist the handlebars. If the stem fails to move try this next step.
Remove the front brake, and try to get the expander wedge to drop out through the bottom hole in the steering column.
You must remove the expander wedge completely. If it won’t drop out, you may need to use a file or a Dremel tool to make the hole at the bottom bigger.
Sometimes you can screw the expander bolt back in again from the bottom and pull the expander wedge out. (Picture right.)
Now you can insert a piece of ½ inch diameter steel bar up inside the stem from the bottom side, and drive the stem out with a hammer.
Put some duct tape inside the fork blades to avoid chipping the paint with the hammer.
Ammonia, a common household cleaner, will also loosen aluminum corrosion, so you may also try soaking the part overnight with ammonia before you try to remove it. Ammonia is also corrosive to aluminum, so this is only a short term temporary measure.
The boiling water trick will also work to remove the crank arms from a bottom bracket spindle, if the extractor threads are stripped.
Only in this case, after pouring the boiling water over don’t wait for it to cool; you need the aluminum crank or chainwheel to expand away from the steel spindle. Drive the crank off while still hot, using a piece of wood and a hammer.
Because prevention is always better than a cure, make sure when you fit your stem or seat post, you apply grease to the inside of the steel frame, and to the aluminum component.
The grease will seal out the moisture, and stop the steel and aluminum from contacting each other. Remove your stem and seat post at least once a year and re-grease. More often if you ride in the rain a lot.