BSA Bottom Bracket Replacement So I have an old Winora City bike here and I am willing to spend a few hours in maintenance and repair of the bike. However, I am still a novice in the field and would like to gain some experience.

I feel the most urgent part to be replaced is the bottom bracket. The screw which holds the crank to the bracket constantly starts loosening itself on the left side. Loctite helped only temporary. 

Concerning the parts I need to buy, I am very confused. First of all, a bike mechanic once told me the threads are BSA. The spindle is a square taper, J.I.S.-like, which can be seen here: Sheldon Brown's Bottom Bracket Glossary. Contrary to most bikes, mine is with an outer thread and the brackets are held in place by a nut (no screw).



On the drive side there is a single gear, type Sugino 48



I am wondering right now how to replace the bottom bracket. But before starting and interrupting half way because I don't know how to proceed, I would like to ask you whether I am on the right track:

I presume that the first step is to disassemble the bottom bracket. For the drive side I found (as can be seen on the picture) that I have to use a pull tool.
Next, I need to precisely measure the length of the shell. It looks to me like a 68mm, but might as well be 70mm. 
Then I can select a new set of spindle/bearrings. Am I restricted to those "cup and cone" bearring sets? Should I buy another type? What is a reliable and well-to-maintain solution here?
It seems to me that the thread on either the crank thread or the nut is somewhat damaged.

If this is your daily ride and you are not going to take it for around-the-world-tour, I'd replace the bottom bracket with a cartridge one. It doesn't require any adjusting - great advantage if you are a novice.


Measure the shell width (you can do it without removing the spindle, just flip the bike) and make sure it is 68 (typical BSA). 
Get yourself a crank puller (simple tool for couple of bucks), pull the cranks and measure the spindle length (just measure the tapered parts, discard the threads) and check whether the spindle is symmetrical (i.e. the length from the middle of the bottom bracket to the left and to the right of the spindle is the same).
Check what kind of tool you need to remove the drive side cup. When attempting to remove it, remember that at BSA, the driver side has reverse threading (you unscrew it CCW).
Purchase the stuff you need and put it on the bike. The cartridge bottom bracket has its left and right (driver) side marked.


Good luck!