Originally Posted by
zacster
Before you switch the bottom bracket maybe just find a square taper/JIS compact crank and just swap those on the existing BB/spindle. You'll end up a lot closer to what you already have that way and won't have to fiddle with anything else. I looked on ebay and they are available.
Unless OP gets the square taper crank for cheap (co-op etc.), he would invest a lot of money in an outdated BB standard. that BB may be on its way out anyway. You can get Deore external BB for $15, a crank is $60 or some other significantly higher price. BB are wear items, the crank may live for nearly forever.
OP: you also should check BCD of your cranks if you can install smaller chainrings. Check local co-ops if they have old stuff for cheap. there should be thousands of old square taper cranks flying around.
Edit: check the
gear calculator to see if you need to adjust cassette in addition to chainrings. As many mentioned here, a sub compact crank is more suitable for mere mortals. Not many people are able to spin out a 52:11. Going from 39 to 34 may not be enough. Once you go through the expense of replacing half the drive train, you may as well get 100% of the result you desire.