Hi guys, quick question.

I've got an older MTB (Schwinn Paramount Series 90 from around 1995) that I'm getting back into ridable shape. It's pretty much done, but the bottom bracket's shot. Someone overtightened the crank bolts, and stripped the threads out of the spindle.

Shouldn't be a problem, I've got a spare from an earlier upgrade.

However, the thing won't screw into the threads. The spare BB came out of a road bike. It's just a cheap square taper. THe threads on both the frame and BB look fine, they just don't match.

The original BB in the schwinn is the older style, not a sealed cartridge. They look pretty closely matched, but they're obviously not, since they don't thread.

Is there something I should look for when buying a new BB to make sure it's the right one?

Unless the other bb is campy they should be the same. I don't want this to sound insulting, but are you sure you're just not putting it in the wrong side first or turning it the wrong way? I've spent ten minutes swearing at a bb till I realized I got turned around.

Have you tried both sides or just the fixed cup?

The fixed cup (right side) is reverse thread (assuming it's not Italian thread, which I do not think Paramounts ever were) and if you have tried only that side but are screwing it backwards...

Well, you get the idea.

Ended up taking the bike to my LBS. Decided that I'd just pick up a BB that fit, and I'd have the frame with me to make sure I got the right one. I was thinking maybe it was English threads or something weird like that.

After confirming that the threads were indeed weird, the mechanic noticed a couple weird spots in the threads. Looks like someone probably put too much weight on the cranks or something that widened the threads on the bottom side very slightly.

Long story short, he ran a chase tool through it, and installed the new bb, good as new.

Glad it worked out well for you.......You're under the wrong impression about English threaded bottom brackets being "weird," though. Nothing weird about them, they're extremely common, and are an excellent design since the drive side of the bottom bracket and shell is reverse threaded to offset a phenomenon called "precession," which causes the driveside of a bottom bracket to loosen if it's not reverse threaded (Italian threaded bb's, for example, are right hand thread on both sides and have a tendency to loosen on the drive side because of this) . Your Schwinn is undoubtedly English threaded-

Undoubtedly. Though I didn't mean weird like odd, just unusual. I basically just guessed it was a slightly different threading based on Sheldon's BB info, which it looks like I'd misread or something. Thanks for clearing that up though.