bigredkevbot

So I posted a while back that I was starting a fixed gear build; this weekend I started said build, but to my utter disappointment my bottom bracket choice was not sound.

Here's what happened:
I have a (most likely) 80's Taiwanese bike frame that I love (skinnier steel tubing). Its a bike I truly feel comfortable on, so of course, I absolutely destroyed it to make it into a fixed gear.
The bike has an old-school Cup and Cone style bottom bracket (so your crank is affixed by tightening a nut onto the bottom bracket, whereas most modern bottom brackets work by threading a bolt into the BB itself). I bought a new JIS (Japanese Industry Standard) square taper BB (Shimano UN-55 or something): basically a more modern sealed cartridge bearing BB. AND IT JUST WON'T FIT I greased it this way and that, tried doing one side, then easing the other in, and vice versa, switching sides, everything I could possibly do before giving up and putting my old BB on (Only to find that it won't go back on entirely tightened, and it causes my chain line to look line **** (excuse my language).

So I need some help, the only thing that I have been told so far is that a threading tool shows that the threads are fine but they might be "tilted" causing one side of the BB to screw inwards and upwards while the other goes inwards and down).

Do I try and buy an old school BB and replace the one I have now (which is nasty as hell, despite a good clean), or do I try and find a sealed bearing cartridge that works?

Thanks,
Red

CbadRider

Moved from SS/FG to Mechanics.

bikeman715

Yes it might need to go to the shop to have the BB treads look at . If they not to bad ,they use a chaser to clean them up , sometime re using your old cups and try to clean them up . If they too bad then they need to be re cut .

bikemig 

If the old BB cups can't be screwed in flush to the frame, you probably have a cross threading problem. Have a mechanic chase out the threads for you. You might as well have him (or her) install the Shimano sealed unit at the same time.

Normally there should be no problem swapping out an old school cup and cone square taper BB and installing a Shimano sealed unit. In fact, it's a nice upgrade since you don't have to overhaul your BB.

Also sometimes it can be hard to start a BB and you need use your sense of feel to figure out when to start threading.

Still if either of the cups (fixed or adjustable) aren't flush against the BB shell, you probably have some sort of cross threading going on. It is fixable and if not, there are solutions.

HillRider

I wonder if your old frame is French, not Tiawanese and has a French bottom bracket. The threads are similar but not interchangeable at all. Do your old bottom bracket cups have anything engraved on them? Maker's name, some numbers, anything?

Andrew R Stewart 

Possible issues preventing threading into the shell of a BB cup (or complete cartridge unit).

As mentioned- thread standards incompatibility.
Frame shell threads are bungered up or not cut as fully as needed.
The BB cable guide securing bolt sticks into the shell so far that it hits the cartridge and sets it off center. Or the cartridge isn't started completely coaxial to the shell.
A portion of the tubes that enter the shell are sticking in too far. see above.
Some damage to the shell or BB unit has happened without the OP's knowledge.

Really this is a hard problem to deal with without everything in hand. The suggestion to go to a LBS is the best one yet. Andy.

FBinNY 

It's time for some diagnostic experimentation. Thread both cups in without a spindle. Check of the flange on the fixed cup and a lokring on the adjustable cup lie flat on the BB face. Perfect flatness isn't ultra critical, but they need to be flat within a quarter millimeter or so. If they pass this test, I suspect the threads are OK but slightly off a common axis, which is fairly common. It's not a problem with cup/cone BBs, but can become one with certain cartridge designs.

You might be able to use your cartridge BB. Try to thread both sides in simultaneously, working by degrees, and first making sure that the threads and mating parts of the BB are well greased. This often woks because it splits the error in misalignment so do whatever it takes to earn good Karma and give it a shot.

Otherwise, stick with the working loose bearing design, and simply buy a spindle of appropriate length for the chain line you need.

bigredkevbot

So I had a mechanic at a reputable shop thread the BB and he said it threaded fine, he then tried to install the cartridge BB and said that he could only get it so far in before it just would not budge.

I tried easing both side in bit by bit, but they still refuse to give and sink into the threads more than a rotation or two. I am considering buy a new (used) spindle to remedy my chain line issues (and I found a very very very cheap one online). I also think the original BB may have had a tough time going in as it did coming out, so more force may be necessary (or grease).

I did not however remove the cable guides underneath the BB shell because I did not see anything inside the shell when I was cleaning it to indicate that there might be something pushing against the BB. Regardless I will try to remove them to proactively alleviate this issue.

hueyhoolihan

good idea to remove BB cable guides. IIRC there was a guy on here who had a similar problem with threading the BB, turned out the cable guide bolt was acting as a stop.