The BB on my 1987 Fuji TT bike feels a little crunchy when I get out of the saddle and mash.

Is this a BB problem? Should I ride it until it fails or change it out?

How hard is it to change out the cartridge?

It is a 68 with a square spindel. I don't know the length. What should I use as a replacement?

Thanks as always.

RFC

Don't overlook the possibility that the problem is in the pedals. In my experience "crunchy" as you put it most often comes from the pedals as do squeeks.

If you have to change the BB, it is an easy thing - especially if you are replacing a cartridge bearing. The question is whether or not you have the correct tools for the job. If you do, it is as easy as putting a hot dog into a bun. If you don't have the right tools, it will be like putting a bun inside of a hot dog.

Go to https://www.parktool.com/repair/. Search for "bottom bracket repair". Read.

Sheldon's site will help you through it.

I just realized that I still have a Sheldon wallpaper up.

Thanks all. Overhauling the BB is the one basic piece of bicycle mechanics I haven't done (actually I haven't built or trued a wheel yet).

Here is the really dumb question. In order to determine what I need for a replacement, do I need to pull the existing cartridge first?

That would be the safest thing to do. Are you sure it is a cartridge? It wouldn't be unusual to find an adjustable BB in that era Japanese bike.

The easiest way to overhaul an older adjustable bottom bracket is to take it out, clean out the threads in the shell, and pop in a brand-new Shimano sealed unit and forget about it for the rest of your life. The Shimano units aren't that expensive (and if you want to spend less, I've seen Nashbar-branded units in their catalog that look halfway decent).

It's easiest to measure if you have it out of the shell, or at least have the rings off.
If it's a cup & cone type, you might be able to overhaul it with new BB's & grease. I can get new BB's at my LBS for $.05 each, so $1.10 to do both sides.
IF the spindle or cups are pitted, it would be a good time to upgrade to a cartridge. Replacement parts, IF available, cost too much to be economically feasible.
IF you have an older C&C type, you have to note if it is built with an offset to one side. Both my MB's were built with the drive side 3MM longer than the NDS. Since cartridge types only come in a "symmetrical" style, the replacement cartridge had to be an additional 3MM longer than the existing spindle. That moves the NDS crank out 3MM. See-
https://sheldonbrown.com/harris/botto...ets.html#axles