I am in the process of replacing my tripple crank with a double.
I just removed the old crank arms and BB, I will need a new BB so that both of the double crank arms are the same distance from the center of the bike.
In trying to determine the correct new size BB I installed the double arms on the originall BB and can see a 5mm farther distance on the drive side.
The original BB is a Shimano BB-UN52 68 and under this it says BC1.37x24. What does this mean? I believe the overall BB lenth is 113mm mesured with a ruler.
Do I need a 109 in order to eliminate the 5mm defferance? Is all of the differance on the drive side??
Well I just figured out what the BC 1.37x24 means. Thats the thread of the hole in the bottom bracket itself.
I think that most replacment BB's come with the lenth of the spindle printed on the outside but perhaps the fact that mine is an OEM it doesnt have the size listed.
Still need help with the over all length for the double crank though.
For anyone who may have been following this thread.
After doing the research and playing around with my set up I have found that the original BB 68X113 works just fine for the tripple Sora crank my new 105 double. When installed properly both crank arms are centered with the frame.
I was lead to believe by another thread that I would need a different lenth BB when swaping over from the triple to the double but that is misinformation.
All is well in West Central Wisconsin and I will be riding the bike soon.................................
