bark_eater 

I just installed a UN_55 bottom bracket and the left aluminum "cup" is not tightening down all the way down to the BB Shell. The gap between the "cup" flange and the BB shell is about 1 mm. the threads are not crossed. I did put some grease inside the "cup" that might be caught and a hydraulic block. Is this gap with in spec? I don't have a torque wrench set up for this, but I got it pretty tight for aluminum threads.

Bike Gremlin

It should be fine - as long as the right hand cup is tightened first, all the way. And, of course, there's no play in the axle. It should even feel a bit "rough" when turning the axle with fingers, unlike wheel bearings.

wschruba

Some of the confusion might be in the terminology--it's a retaining ring, not a cup. While it has a lip, it is designed to seat on the face of the cartridge.

In fact, old models don't have the lip on the retaining ring.

andrewclaus

Are you putting a 68 mm cartridge into a 73 mm shell? Read the label and measure the bike.

bark_eater 

That was my assumption. There was a little bit of bind on the bearings that seemed like it was related to to the retaining ring torque, but also seamed to go away after spinning the shaft a dozen times.

ThermionicScott 

fietsbob

Add a spacer to the left side, to tighten it against ? you could..

ThermionicScott 

Absolutely no point to that, and it could interfere with the connection between the NDS cup and the cartridge.

fietsbob

All depends on the gap thickness being matched by the spacer thickness, the gap seemed to bother him..
doesn't bother me at all..









..

Metaluna

I've seen this gap on a couple of my steel frames, even with the BB shell reasonably within tolerance (e.g. 67.7mm). I usually torque the drive side to spec, then just tighten the NDS "good and tight" and check to make sure the axle isn't binding. Seems to work okay for me.

The only downside is that, if you had your BB recently faced, the gap will leave bare steel open to the elements in an area that's exposed to a lot of water spray (possibly salty water). So you might want to seal it with a little touch up paint.

bark_eater 

I'm going to fill the gap with grease.

djb

in my opinion, that will just attract dirt and whatnot, so consider using some caulking or something. Bathroom caulking or the like will stop accumulation of dirt, wont be sticky like grease, and can easily be removed if need be.

have never done this, but very recently installed a new square taper and there was a very slight gap also, but not enough to concern me--but your experience made me recall the gap, and the caulking idea just came to me.
I guess other stuff you have around the house could work too, I dunno--rubber cement, flexible glue, anything that would do the job but still be easily scraped out if you needed to retighten it.

base2 

Silicone caulk is just wrong. It gets into the pores of the metal & nothing will adhere again, ever. Also, silicone caulk off-gasses & creates a mildly corrosive environment in enclosed spaces. I know it's commonly used for lots of things, but if you have electronics enclosed in a box & used silicone caulking to seal out the weather, soon you will have a liquid filled box of corroded electronics. Common knowledge in the hobby electronics community. Secondly, the only thing that sticks to silicone is silicone. So your "seal" is only temporary at best since by extension it won't actually adhere to the surface you are trying to seal.

Latex based caulk is the better, longer lasting, solution that actually does what it says. It's easy to find. It's the one labled "paintable."

That being said, good ol' fashioned grease is fine to fill the gap for corossion protection/water infiltration if those are concerns you have. Some bb cups don't have a lip at all. In either case, I say screw it down & call it good. The inner bore of the cup very closely matches the outter bore of the bb cartridge. That's where the support comes from.

djb

just ideas here, I'm not a caulking expert. I have used the paintable stuff a fair amount, but in the end maybe caulking isnt the best idea.
Wax or something soft, but wont gunk up with dirt like grease?

again, just ideas here. The slight gap on the old bike I fixed up recently didnt bother me, so I guess the person in question here will make his or her own decision, and there is no reason to try something and remove it--but thats good information about silicone caulking and the downsides, thanks.

ThermionicScott 

You guys need to stop worrying about that little gap. It's actually a good sign that the bottom bracket is making firm contact everywhere it needs to -- inside the shell.

wschruba

OR, you could just stretch an appropriately sized o-ring/rubber band over it, which has the double whammy of keeping crap out, and being 100% reversible with no painful cleanup.

djb

how about squishing some wax in there, not as reversible as an o ring thingee though.

on the whole "keeping crap" out angle, many many years ago I had a bike with square taper that had developed a creak. The bearing felt ok though, so removed the bb, and was surprised how much grit had worked its way into the grease in the threads, cleaned everything up, slapped a lot of new grease on the threads, reinstalled it and it made the creak go away and was good for a few more years.
the creak was probably from having loosened a bit, but I was frankly surprised by the grit-mind you, that bb was probably the original, about 15 years old, and easily had 20,000kms on it.