Bicycle Mechanics - Dismantling a shimano sealed bottom bracket

Howdy
I have a 'sealed' shimano bottom bracket, pretty much the same as a un-72...Does anyone know if these can be taken apart to regrease/ have a look at bearings? I've removed the seals on both sides and have unscrewed a thin nut and spacer from the axle, but there's another threaded 'nut' with under a mm of access to get what looks like a speciality tool onto it.

Has anyone done this, know the procedure etc...???

There's a reason they are sealed ... to keep inquisitive folks like you out! No re-greasing needed. When it wears out, you replace it. It's called progress, an improvement over the loose ball bearing styles of yesterear.

I agree that one should be able to repack a bottom bracket. Have also tried to pull a sealed cartridge apart, to no avail. I think they're stupid, and represent everything that's wrong wth our disposable society. What do I do with a 2 lb. hunk of metal after I replace it?

The transfer station where I live recycles metal. Try that.

There's a reason they are sealed ... to keep inquisitive folks like you out! No re-greasing needed. When it wears out, you replace it. It's called progress, an improvement over the loose ball bearing styles of yesterear.

lmao -- throwing stuff away is an improvement

My 7700 DA BB (loose ball/roller) was a work of art. Light as hell. It finally died, but it lasted a LOT longer than sealed, and it was so nice to look at during repacking.

Or you could have taken 1/4 of the same time and just thrown a new D/A track BB in it...

Or you could have taken 1/4 of the same time and just thrown a new D/A track BB in it...

Good option, DA Octalink is not sealed.

On the recycling front, I highly doubt that any operation is going to take apart the BB to separate the metal from the plastic. They are going to accept the BB at the transfer station and then throw it in the dumpster. That sucks, in my opinion.

Or you could have taken 1/4 of the same time and just thrown a new D/A track BB in it...

That means mail order or a trip to LBS, followed by giving up some of my $$. Insead, I got to spend some time in the shop unwrapping some engineering porn -- then rubbing it. :D

I agree that one should be able to repack a bottom bracket. Have also tried to pull a sealed cartridge apart, to no avail. I think they're stupid, and represent everything that's wrong wth our disposable society. What do I do with a 2 lb. hunk of metal after I replace it?

Which is amusing since it's typically the cheap throwaway bikes that HAVE the servicable BBs.

A Sealed BB Provides lots of smoothness at the expense of rebuildability. Part of the reason these things aren't servicable is to make sure people have to keep buying em to keep production up.

Yeah, one can make a good looseball bottom bracket that is nice and smooth and rebuildable. But it's going to be a lot more expensive.

Personally I prefer cartridge BBs. It isn't a silly change like Integrated headtubes or a confusing change like having 4 and a half different bottom bracket shells for BMX bikes. It's a legitimate improvement over the old system in many regards.

Which is amusing since it's typically the cheap throwaway bikes that HAVE the servicable BBs.

A Sealed BB Provides lots of smoothness at the expense of rebuildability. Part of the reason these things aren't servicable is to make sure people have to keep buying em to keep production up.

Yeah, one can make a good looseball bottom bracket that is nice and smooth and rebuildable. But it's going to be a lot more expensive.

Personally I prefer cartridge BBs. It isn't a silly change like Integrated headtubes or a confusing change like having 4 and a half different bottom bracket shells for BMX bikes. It's a legitimate improvement over the old system in many regards.

My experience has been that "disposable" sealed bottom brackets last at least as long or longer than "servicable" cup and cone bbs, even those with relatively frequent maintainance.

Cup-and-cone bbs do wear out. The spindle and/or cups eventually pit and you have to replace them so they aren't lifetime purchases either. Just a lot more work for the same outcome.

I just changed to a Pil Wood BB, and was really impressed. Replaceable bearings that are better ones, too. bk

I've pulled apart my Ultegra BB that has sealed cartridge bearings.

Here's what I did:

- Pulled the crank leaving the outboard bearing BB in the frame.
- Carefully, using a screwdriver, pop off the plastic cover that snaps into the spline area of the bearing cartridge. It should be over top of the bearing seal.
- Carefully, pry out the seal, exposing the bearings.
- Leaving the bearings in place, flush out the race with some degreaser, cleaning the bearings and race as much as possible.
- Flush out the area with WD40, wiping any excess out.
- Repack with grease. I used Pedro's Syn Grease.
- Replace the seal.
- Coat the seal with grease only where it tucks under the edge of the bearing housing (to help keep contaminants out of the bearing.)
- Replace the plastic cover that presses into the spine area of the bearing
- Do the other side
- Replace the crank.

My experience has been that "disposable" sealed bottom brackets last at least as long or longer than "servicable" cup and cone bbs, even those with relatively frequent maintainance.

Cup-and-cone bbs do wear out. The spindle and/or cups eventually pit and you have to replace them so they aren't lifetime purchases either. Just a lot more work for the same outcome.

Oh, Cup and cone BB's definately do wear out and I won't argue that. But it is possible to service the individual components as opposed to just replacing the whole unit. I run Sealed BBs on everything but my schwinns (American BBs, don't have much choice short of running a conversion bushing) because they last darn long enough for me.

I just changed to a Pil Wood BB, and was really impressed. Replaceable bearings that are better ones, too. bk


i had to have my phil BB rebuilt at 11k miles and then again at 7k miles. i get much better mileage from a UN-72 and get about four for the price of one phil BB :eek: .

ed rader