The lockring on the bottom bracket keeps loosening up, it's now ~15-20km. What can I do to prevent it?
The steeper the hills I ride the quicker it comes undone - it's a single speed so it's clear and I guess expected that the higher the forces the quicker it will loosen up.
UPDATE: I have lockring tool which I use on my commute rides which is wrong size. The lockring was tightened by bike mechanic 2 weeks ago using a proper tool, but it came loose within 30km.
UPDATE 2: When the lockring becomes loose it causes a click in the BB. If I push the left pedal it will click and then if push the right pedal it will click again. In other words, if I put one of the pedals up I can make the BB click if push/pull the crank towards/away from the seat tube.
UPDATE 3: After I removed the cranks and the locking, it turned out that the non-drive side BB cup is not tight in the BB thread. I really mean the cup, not the spindle. Even when the cup is fully screwed in (so the spindle turns freely but doesn't have any wobbles) I can move the cup up/down/left/right. It's a tiny movement, but it's observable and visible to a naked eye. It's as if the cup is of wrong side. The threads on the cup and inside the BB look ok, but I haven't cleaned them yet.
If I put locking on the removed cup it also isn't tight. It seems it fits, but there is tiny sideways movement.
I don't think this related but after removing the non-drive side cup I still cannot remove the spindle which I think is unusual.