pstock

finally BB question.

for my Sam Hillborne (68mm BB shell) I first tried to use a BB-UN26 that I have lying around. It is marked 68mm
BUT
1) on the DS there seems to on oddly thick 5mm flange, thicker than any of my other BB's (UN5x, UN7x)




and
2) I was not able to get the NDS cup seated all the way in. it seemed to bottom out with about.... 5mm still to go.

does that make any sense?
why does this BB had such a thick DS flange? (does this have something to do with 73mm BBs?)

Andrew R Stewart 

1- The driveside flange has no bearing (pun) on how the BB fits or what the chainline is or what the shell width/BB specs are. One secures the flange against the BB face regardless like the photo shows. It's just what the manufacturer decided to do with this version of their BB.

2- The other side's retaining ring (some will call it "cup" but it is certainly not a cup like shape) is a compression fit. It will go into the shell AND over the left hand cartridge's end only as far as the tapered compression fit allows. However that ring is cracked and while many have done so (being only plastic, one more example of a poor material choice chasing lowest cost points) once in place the crack is generally not an issue. Having said that a crack can cause insertion challenges. Getting the ring to start threading in without the rung distorting and thus the ring's threads not following the shell's properly (sort of like cross threading) and/or the ring not being able to handle the torque that the tool is applying on it can both be a problem.

In the end it's about the cartridge portion of the BB being properly installed WRT the shell, intended chainline and being fully contained so there's no rocking or movement due to the cranks and loads they see. Did you install the crank arms and see how they pulled up on the axle? Did you see if there was any rock, usually by squeezing the crank arm end and chain stay together on first one side then the other? Andy

Bill Kapaun

On BB's with the plastic NDS cup-
I'll seat the DS "fairly tight".
I then screw in the plastic cup "pretty tight".
I then back off the metal cup about a turn.
Seat the plastic cup about the same.
Hog down the metal cup.
Whatever NDS "gap" you have is what it is.

Removal- DS first since plastic tends to break more easily if you don't.

This is how I retain the BB removal tool.

oldbobcat

BB-UN26s and 55s use the same cartridge for 68 and 73 mm shells. The only difference is the inside of the NDS retainer ring. The 73 bottoms out 5 mm earlier because . . . It looks like someone switched rings on you. See if your local shop has one for 68 in a used parts bin.

Murray Missile 

I know I'm late to the party but for future reference I've installed several 68mm UN26 BB's (more than 10) over the past few years and they have all done this same thing, the NDS cup stops about 3mm short of being seated and it reeks havoc with my OCD.

ign1te

On some of the shimano spindle lengths, they state that it is intended to use together with a chainguard or similar. This means that the "effective" shell width is 70 mm or some such. If you had placed a 2 mm thick chainguard mount on the DS, the NDS cup would be flush on the other side.

Bill Kapaun

Instead of taking a chance to break it while "driving it home", I seat it first and then drive the metal cup home.
Pity the person that tries to remove the NDS cup first. For that reason, I always install the metal cup last and remove first.
I figure the plastic/nylon?? cup is only going to deteriorate from age/UV exposure and get weaker. Why strain it?
One could maybe make a point that they designed it backwards? Insert the cartridge from the NDS and let the plastic part be in the shade of the crank.
More logical is avoid plastic on a stressed part.

Murray Missile 

I do them the same way, I just refurbished a 1985 Fuji that had been changed over to a triple back in the 90's and switched to a 68 X 117.5 UN-26 BB with the plastic cup somewhere along the way except the NDS cup on this one went in all the way. It was an off white color not the black or gray I've always seen. This bike had seen numerous RAGBRAI rides BITD and the bike showed it but the BB was fine and the cup aside from being dirty was also fine so after a good wipe down they both went back in.

I have a couple NIB UN-26 BB's I bought several years ago that didn't give the correct chainline so they went in the parts bin. After thinking about this thread I pulled them out to look them over. I had never noticed before but the BB's were UN26-E's for "E" mount derailleurs. These were Ebay buys from a few years ago and I had been buying my BB's from one particular seller back then and these were sold "not in retail packaging". Now I wonder if all this time I had been using E bottom brackets that would have required a shim to take the place of the derailleur bracket? That would also explain my chain line issue using what should have been the correct BB spindle length. I feel pretty dumb now, oh well, live and learn! I no longer switch my older bikes to cartridge BB's, I keep the old 3 pc. or replace it with the same type if at all possible but if I do ever have need to use these E brackets I will know to put a spacer on the DS unless using an E bracket and I try to avoid that whenever possible.

Murray Missile 

Just saw this after my post above, yup, I'm 100% certain that's what happened but I didn't have the retail packaging back then and wasn't as "conversant" in Shimano PN's as I am now. Even had I noticed that E on there it wouldn't have raised a flag. Hopefully this will help someone else down the road.

UPDATE: Taking another look the UN26 E's they have about a 3mm gap between the DS flange and the threads so I don't think they would have threaded all the way in anyway. I found a new DS cup in a box of other parts, I have no idea where it came from but it goes on the BB's all the way and measures 68mm between the flanges. It's slip fit on the BB but there is no discernable "slop". Now if I could only figure out where it came from....... I'm going to take the old cups I hone the ID so they'll just slip over the BB and seat against the BB shell.