Getting to the bottom of things, we have the bottom bracket. This is a part of the bicycle we do not often think about. It’s down there, at the bottom of the frame, home of the spindle – the place where the cranks connect. Unless the cranks don’t move, or there is a strange side-to-side movement when pedaling we don’t usually have to think much about it.
Here is a square taper sealed cartridge bottom bracket on a Boston-8:
Most often it is the case that long periods of time will pass – think thousands of miles – between needing to change out the bottom bracket. This is especially true when it is a sealed cartridge. However, in our case this is for a custom build and some things need to be switched out. The squared off ends are where the cranks attach. We’re putting different cranks on this particular frame, cranks that require a different bottom bracket.
This bottom bracket has splined ends, and so we used a bottom bracket tool with splined ends that match up, a washer and crank nut to hold it in place, and a very large wrench. Most bottom brackets have one side that is reverse thread, meaning you would turn in the opposite direction than normal to loosen. This can vary depending on the type of bracket and frame, and so unless you know what you’re starting with, it takes some experimenting to determine which side is reverse thread. For this particular instance, the drive side is reverse thread. We found that out after inadvertently tightening on the first try.
You get something like this out:
We have here the very large wrench, splined bottom bracket tool, a sealed cartridge bottom bracket (missing one side), washer, nut – and a chain tool that really had nothing to do with this operation at all.
Once the old bottom bracket is out we have a fresh canvas, as it were, to put together our custom build.
Next step is to install our new bottom bracket…