s1xty7

So I started bike commuting to work a couple times a week last fall (on a 1987 Diamondback Topanga mountain bike), took a few months off during winter, and I'm now back to commuting by bike. I don't know a bunch about bikes yet, but I'm eager to learn and am fairly mechanically adept. I'm also a Clydesdale. Thought some background might help.

Anyway, riding the other day and my Sugino VP (170mm) left crank arm fell off. Reattached the nut and it did it again. I guess that means new crank arm, but the arm is original equipment and it doesn't appear that I can track down a direct replacement very easy. My bottom bracket has some play in it and I've been considering a wider range of gears for commuting (flats to 12%+ grade) so I thought about just getting a new BB and crankset (say 48/36/22; might have to replace a small 26 with a 22 to make that happen). Only problem is, I have no idea the size. I like to overbuild things and have considered taking longer trips with this bike so I was looking at more touring type stuff. A lot of people seem to be fans of the Sugino XD-600 and the Shimano BB-UN55 (separately), but I don't know if those will play together well or how to determine the size BB I need. In fact, I'm a bit fuzzy on exactly what BB measurements refer to even after reading about it for an hour or so.

So, in summary, I need help determining what size parts I need, what parts would be recommended for a touring type setup with a hill-climbing low, or a good source of Sugino VP cranks so I can just bolt on a replacement.

Thanks in advance and I will try and answer any questions as best as possible.

s1xty7

JohnDThompson 

Any square-taper arm of the appropriate length will work, if you don't mind a cosmetic mis-match.

ThermionicScott 

"Bottom bracket has play" -- could be worn, or it might just need adjustment. Old-school Sugino cranks are easy to come by.

oldskoolwrench

With your existing Sugino VP RH crank arm, the smallest inner chain ring you can use is a 24t (74/ 110 BCD).

If you want either a 22t or 20t inner chain ring, you'll have to change the entire Crank and BB to a Compact Drive crank (58/ 94 BCD), and change the Ft. Derailleur to match the Compact Drive crank.

Your best bet is to replace the existing inner chain ring with a 24t, and pick up a generic LH crank arm; just match the length of the new one to the old (it should be stamped on the back side of the RH crank arm).

Open up the BB and inspect the spindle, cups and bearings; replace as necessary with the same length BB spindle and/ or cups.

gyozadude

If you're not worried about top-end gear ratio, get a 44x32x22 Vuelta Montagna crankset ($25-$30)and Vuelta cartridge BB ($14) at vueltausa.com or some place like that. Check their daily specials area and see if HG compatible chains for 6/7 spd are still $4 and get a new chain too.

SweetLou

Well, he would need to know if it is a square or a diamond. Also, if he replaces a low profile crank with a straighter crank, he could have issues with the chainstay.

s1xty7

And that right there seems to be the winner. I could spend a ton of money going through gears and upgrading this and that, but I got a Sugino Impel crank arm for $12 and a Sugino 24t chainring for $20 from bikeparts.com. Cheaper than what I was looking at doing (although $20 for a single chainring seems expensive, but it will also let me know if that is the gearing I want or if I need to go lower at some point in the future).

Thanks for all the suggestions. I'm hoping the crank arms aren't too different. The pictures of them look similar.

s1xty7