I was working on a Fuji Thrill mountain bike from the late 80s this weekend. I figured the bottom bracket might be toast, but from just spinning the crank, it seemed fine. There was no lateral movement, no grinding noise.
However, I decided to take the crank off anyway and when I did I noticed that the BB sounded like it had sand inside instead of bearings.
Is there a way you can figure this out without taking the crank off?
No, but the grease was pretty much gone. I took the bearing cages out and immediately bearings fell out. Luckily I didn't see any scoring on the spindle or the the cups... I replaced with new loose bearings, lots of grease and it seems OK. My guess is that this was the first BB service in 20 years.