Originally Posted by Barabaika
You'll get huge weight saving because UN54 is plastic.
But overall it's a good bb.
has high quality Tange bottom brackets:
The UN54 is still metal, the only plastic (phenolic) parts is the non-drive side cup. The 54 combines the weight reduction of the 73 (hollow spindle) with the pricepoint of the 53. Basically Shimano combined the two lines into one.
Why do you say your crank doesn't work with the old bb?
This is Africa, 1943. War spits out its violence overhead and the sandy graveyard swallows it up. Her name is King Nine, B-25, medium bomber, Twelfth Air Force. On a hot, still morning she took off from Tunisia to bomb the southern tip of Italy. An errant piece of flak tore a hole in a wing tank and, like a wounded bird, this is where she landed, not to return on this day, or any other day.