I have an old Bianchi Limited road bike converted to a fixed gear. I think it was still using the orignal bottom bracket up until today when I was powering up a hill and all of a sudden the bottom brack just snapped and then popped out.

Anyway now I need to get a new bottom bracket. How do I know what type an size I need to get? I have a formula rear flip flop hub and 126mm spaced droupouts. Any help?

what cranks?

Right now the bike has the original cranks and I can not tell what they are. They only branding I could find said "SR" and the chainring has 42 teeth. Would it be wise to get a new crank now too or is that not necessary?

probably unnecessary to buy a new crank, though if you have the cash I'd do it because a newer crankset is probably lighter. I would say something between 107 and 110 will put you in the right ballpark for your rear spacing, pending some clever work with washers/spacers/flipping chainrings etc. Maybe look at the old bottom bracket spindle and see if there is a number in the 100's marked (probably 105-115ish). That should be the spindle size you need.

Edit: take some pictures and we can probably help better.

Ok, I'll take some pictures of the BB when I get home from work tonight.

How was the chainline with the old BB? You should be able to find the measurements of it stamped on the spindle or cartridge shell. If the chainline was good, get the same length. If it was off one way or another, get a longer or shorter spindle.

I always thought the chain line was good by eyeing it, but I was never too anal about it.

I could find the following markings on the bottom brack "Nikyo made in Japan 1.37" x 24T" I don't see that number in the 100's you guys mentioned.

did the BB spindle actually snap? Can you show a pic of the damage?

look for numbers on the spindle not the cups.

The bottom bracket is still sitting in the bottom of the bike and I don't have the tool to remove it, so it is very difficult to see anything on the spindle.

Now that I am looking at Sheldon's site it looks like the cap busted off some how, then the cone (?) slide out and dropped a couple bearrings. The spindle itself looks like it is in tact because I can't remove it until I take the crangs off.

So I'm thinking about buying a new sugino RD crank set and a sugino BB. If I go though route, first is there any chance there could be a problem with this setup, and second what size BB should I get?

Sugino 103mm, but there have been reports of chainline issue with newer RDs.

A sugino 103bb with the sugino RD cranks will give you a 45mm chainline, just a heads up.

What does this measurement mean exactly?

Due to the fact that this is a conversion and not a track frame, is there any chance that the chain ring could hit the chain stays?

Also are there any threading issues to be concerned about or are those very rare?

The measurement means that the spindle is 103mm long. The chainline is the distance from the center of the frame to the center of the chainring. 42 is standard for track, but 45 isn't a problem. Plus, you can't find a bb shorter than 103mm. There is a small chance the ring could hit the chainstays, but unless the bike is made for wide tires or fenders, it shouldn't be a problem. Even if the bike is made for wider tires, you shouldn't have any problem with a 42t chainring. If you go to a 46 or 47, you may have some issues depending on the frame. both of my recent conversions easily fit a 48t chainring ( a crosscheck and an old japanese-made road frame) but I had issues with an old Bianchi strada touring/city style bike with anything bigger than 44t.

The only thing holding me back is that I'm a little concerned about putting the 48 tooth chain ring from hitting the chain stays. Is there any way I can measure my bike ahead of time to know if this will be an issue?

why dont you just remove the old spindle and mesure it.
Do you have a pic of this, i don't undestand what actualy snaped and or poped out. (maybe i misread somewhere)

I can't remove the spindle because I don't have the right tools. So I tried to measure spindle length, it appears about 135 to 140 mm. Does this seem like the right ball park? It was origanlly a double crank and I was previously using the inside part.

I took some picutres of the BB. Look at the side near the chain ring. That is the damaged part and where the bearings fell out.

That measurement is way off. You cant measure bb spindle length without removing the cranks.

Your bb may not even be broken, it might have just come loose.

Look, if you really want to do this yourself then sooner or later you will have to get your cranks off and get that bb out. In this case you will need to get your hands on the tools to do it. When the bb is out you can make a proper measurement for a new bb, put the old one back together, or whatever.

I'll have access to the tools this weekend. I was hoping I could order the parts before then so this could take one week instead of two.

Like Mander said, you gotta take off those cranks first.
But it looks like your cup came loose, if thats the case all you need is new bearings and some grease.(any lbs should have both)
Here are some instructions on how to do it:
https://www.bikeforums.net/singlespeed-fixed-gear/208402-maintain-sexy-not-so-sexy-track-bb.html

It means you shouldn't buy those cranks if you can help it.

Thanks that article is really helpful and paints a nice picture of whats going on in the bottom bracket.

I guess my next question then, once I pull out my spindle this weekend and can accurately measure it, am I better off buying a new cartridge BB or servicing this one?

if everything was running smothly before this and if the bb is ok (if it was just the cup that came loose)
i would just service it. Why change it if it aint broke.