I'm installing a brand new BB-UN300 (68x122mm) into a 1991 Specialized Sequoia (replacing the pitted cup and cone BB). Out of the box, the BB doesn't spin very freely by hand, but that's to be expected out of brand new seals I guess.
The problem is when I fully tighten the BB into the drive side of the bike. That's when it barely turns at all, even with the crank arm attached. It's hard to explain how hard it feels to spin, so I'll just explain it like this: crank arm attached, moved up 90 degrees, released, and it goes straight down and stays there, without moving from side to side at all.
Any idea why this might be happening? I would understand it if it happened when tightening the NDS, since that would put excessive preload on the bearings on that side, but this happens with just the DS threaded in. Why would the torque on the DS affect how freely the spindle spins?