can anyone tell me the difference between shimano s BB 's? i took out a BB-UN71 and would like to upgrade a step but hve not been able to figure out what i should get?? pleasae help... thanks

There used to be a UN-91 which was a level above the UN-7X series but all of them but the lower level (heavier) UN-5X and UN-2X are no longer in production. You will have to find one NOS orused.

UN-73 are still readily available. Doubt any noticeable upgrade from a 71 though.

Why do you want to upgrade? What are you looking for out of a new bb?

IIRC, the difference between the UN71 and UN73 is the 73 had the driveside threads as part of the cartridge instead of as a separate cup. It was done to reduce chronic creaking with the 71 design as the cartridge moved within the separate cup under pedaling forces. Otherwise they were the same internals.

weight and longer lasting with out getting that click every revelation after a few months, suggestions?

UN-26's have the DS threads integral with the body.
Buy 1/2 dozen online for about $65 and you can get a free removal tool with the savings.

Weight isn't going to be a huge factor. If you're really concerned with weight, look at the three biggies, frame, fork, and wheels.

As for a solid, square taper, you can't get much more reliable than a Phil Wood bb. A step up won't really get you much more than the time you've been getting with your current bb. Of course, you could always get the a half dozen cheap ones like the previous poster suggested.