Originally Posted by
maagg
Today I managed to remove the BB because it feels a bit hard when spins
I found out that is a BB UN40 68 1.37x24
I wonder if I can replace this with BB UN 300, it says is 68x110mm and 1.37x24 like my BB says but between LR says LL123 (mine says M110)
worth to mention that I will keep using the original crankset
Difficult to follow what you are asking? Which bottom bracket (existing or replacement) says LL123? Which bottom bracket (existing or replacement) does "mine" refer to?
From your photos you seem to have a JIS triple crankset, which you will reinstall onto a new bottom bracket. A JIS bottom bracket has two key measurements: (a) shell width, and (b) spindle length. From what you have asked I can only tell that (a) = 68 mm. The spindle length of the replacement bottom bracket depends on
where you plan to mount your 1X chain ring on your triple crankset: (i) middle ring or (ii) outer ring? If (i), buy a bottom bracket with the same spindle length as your original bracket to maintain the existing chain line, assuming that the middle ring had previously lined up with the center of your cassette. If (ii), buy a bottom bracket with a shorter spindle length. How much shorter? New spindle length = old spindle length - 2 x horizontal distance between the outer ring and middle ring of your crankset, measure from the tip of the teeth.
If you look at my other thread about the 1X conversion of my Trek FX 2, (ii) is the path I followed, because I think mounting a 1X chain ring on the outer ring of a triple crankset looks better. A shorter spindle length also decreases the Q-factor (i.e., horizontal distance between pedals), but I am OK with that because I am more used to the narrower Q-factor of my road bike anyway.