Rusty Seatpost Removal
The unremitting neglect my commuter bike has been subjected to has taken its toll over the years. Usually I only bother to fix mechanical failures, but this spring I decided to replace the rusty seatpost. I imagined it would be a relatively straight forward procedure: pull very hard and it will come out.
Unfortunately the bonding power of rust is significantly stronger than congealed baked bean juice, and cannot be penetrated with fairy liquid. As usual, Sheldon Brown has documented a number of solutions. I attempted each of them in turn, without any success.
The last resort is to cut the seatpost free, which is what I describe below.
Step 1: Cut the top of the seatpost off
First, just cut the top part of the seatpost off with a hacksaw leaving half an inch protruding from the seat tube. This is the part of the seatpost you will later grapple with, so make sure there is enough to get hold of.
Step 2: Cut a slit into the seatpost
This sounds quite simple, but I cannot overstate how laborious it is in practice. It took me about three or four hours to cut this slit. I went through three hacksaw blades. I got several blisters.
You can see in the picture above that the top of the seatpost is slightly deformed at this point, and has a chunk missing. This is the result of repeated hammer blows and a fruitless attempt at pulling the tube out before the slit was complete. I actually tore a chunk out of the seatpost, which should give you an idea of how well rust can bond steel to steel. I recommend skipping this bit.
Step 3: Coil the seatpost up inside itself
Make sure the slit is complete before you start to coil the post, otherwise the saw blade will not sit cleanly in the groove as you continue to cut. I found I was not able to generate enough torque to separate the seatpost from the seat tube all the way to the bottom by twisting alone. So, I hammered a very small screwdriver into the gap I had opened up and lubricated it with WD40. My seat tube is around 3 times the thickness of the seatpost, so this seemed unlikely to distort the seat tube. Nevertheless, be careful if you try it.
Step 4: Pull it out
By this point I was wondering if I would need to cut some more slits, and whether it would be cheaper to simply buy a new frame instead of ten thousand more hacksaw blades. However, once I removed the screwdriver I had wedged in the gap, it was relatively easy to twist the seatpost free.