I'm going to be replacing my crankset with a new (to me) one I got off ebay. It's occurred to me that I haven't done anything to service my bb in the 3+ years (I don't ride a ton so only 1500 miles or so) that I've had the bike and, given the dirty gummy state of the chain when I bought it, I'm not sure the previous owner did anything to it either. So that'd imply that, in the 15 or so years this bike's been around, nothing's been done to it and when I'm pulling the crank anyway, this might be the perfect time.
Currently, the bike has a cup and cone bb with a rather non-standard size (if bikepedia is to be believed) of 68x120 mm. When I bought my crankset, the seller threw in a cartridge type bb (Shimano UN-54) that he said was 68x118 (or maybe 115, but he was pretty sure it was 118). My calipers are at work at the moment, so I haven't gotten around to checking either measurement.
Given I've never serviced or replaced a bb before, if I want to do something to mine, the way I see it, I have 2 options. Buy a bb wrench and pin spanner for the current setup and some new bearings (15 years of abuse, why not drop a few bucks on new bearings) and use the current bb. Or I could pay an lbs to remove my current bb (why buy tools for a one off thing?) and either put in the cartridge bb I have if it's the right size or buy a new one and a tool to remove it.
The first option seems overall cheaper to me ($25-30 for the two tools, a few bucks for some bearings and I've got a bunch of grease), but is that the better option? Would I be better off in the long run going with a cartridge bb? Or should I just leave the bb the hell alone as it doesn't seem to be causing me any real problems, it's just a convenient time to service it and I haven't done that before?
Oh and yes, my current bb and the cartridge are both JIS square taper, so that's not an issue.