Ceramic Bottom Bracket Confusions
 

I bought a Sram red BB from an Ebay merchant. The item description reads:

SRAM/Truvativ GXP Blackbox Ceramic Bottom Bracket Cups - Italian Thread

SRAM's new hybrid Ceramic BB Bearings exceeds the needs of even the most demanding riders. Ceramic bearings are more resistant to dirt and moisture require an astonishing 78% less energy than the next most efficient BB on the market. It features:

Left and right bottom bracket bearing cup set for use on Giga X Pipe cranks with integrated GXP pipe spindle: includes plastic seal/spacer-shell with o-rings
BlackBox (ceramic bearing) and Team (sealed bearing) cups available for replacement: can be used to replace/upgrade XR-series GXP systems
Includes (2) 2.5mm spacers to fit either 68mm or 73mm BB shells
Material: Ceramic balls / Stainless Steel Races
Compatibility: SRAM and Truvativ, Giga X Pipe, GXP cranksets
Italian Thread: 70mm
Weight:
105 grams

I have an italian 70mm shell. When I received the part I held it up to my shell to find that it's too short for a 70mm shell. Looks like 63mm-ish. I was able to fully screw both cups in to confirm that it really is the right thread type. But sure enough, when both sides were screwed in all the way (just hand tight, but flush against the frame) the connecting pipe didn't reach all the way across to the other cup and leaves what looks like an 7mm gap. Rather than just returning the product, and depending on the seller for a fix, I'd like to first understand the part correctly. Learning some self sufficiency is part of the point of doing the service work myself.

My questions for you are:
- Additionally I don't see any spacers in the package (which did appear to be factory sealed). The seller is telling me, "nope that's should fit a 70mm shell. Besides Italians only come in 70mm shells". What could I be doing wrong?
- Is the sellers statement correct or should this product come in differing shell widths? If it does come in different widths, what's the difference? Is it just the length of the connecting pipe?
- What do you recommend here?

Thanks for any help :)

68 and 73 mm wide bottom brackets are English threaded, for road (68) or some MTB (73) frames. The threads are 1.37" x 24 tpi and the drive side cup is left-hand threaded. The English bb from SRAM will have the 2 -2.5 mm spacers used if they are installed in a 68 mm shell.

Italian bb shells are 70 mm wide and the threading is completely different with 36mm x2 4tpi, right hand threads for both cups and no spacers should be needed.

If the cups thread into your bb shell correctly, you have the right one.

So yes, they do thread in. The concern is with the plastic pipe with the O-rings that I believe should extend across and fit into both cups. when both sides are screwed in it doesn't make it all the way across. Isn't that a problem?

I't's I believe, a dust cover for the inside space . mechanically it has no BB axle support Function

have you done an out of the bike test to see If
when the BB faces, are set up precisely 70mm wide , there are gaps?

pick up another O ring, and add it. ?

yes, out of the bike when they are 70mm appart, while the O ring on one side is embedded correctly the O ring on the other side is not embedded, looks like it just barely touches metal, ...barely.

Pick up another O ring? How does that help? Seems like I need a longer plastic pipe?

So from what I understand at this point about the plastic pipe that connects the cups:
- it's intended to seal out water and grime
- it comes as short as the manufacturer dared make it, causing this problem to probably be a common one.
- it probably doesn't save me much wear and tear since the bottom bracket area is well enclosed anyway. (there are only two places that I could see that water and grime could enter - through the threads, and through the hole created by the screw that attaches the plastic cable guide piece at the bottom of the frame).

Let me know if any of this sounds incorrect.

Anyhow. I found one issue that could help there is a decorative/rounded/rubber/circular decal around the BB opening that is not centered and gets between the frame and the cup. Unfortunately this is only about a millimeter thick, so removing it probably won't be enough to allow the pipe to sink into the cup. However It will probably allow the cup to sit more flush to the frame. Here's some visuals.

http://img534.imageshack.us/img534/8...ceramic.th.jpg

Contact SRAM and see if they can send you the instalation sheet for this bottom bracket or give you a URL for a copy on line. Isn't e-bay great?

You know what's worse than ebay? My 666th post!


...yep it's got to be my least useful post. :)

Are you sure the "connecting pipe" aka the dust cover is installed correctly? It only goes in a little on one side, but slides in on the other. Maybe it's in too far. Post a picture of the dust cover installed in the cups.

I'm not able to post a pic of that right now, but Yes I'm pretty sure it's correctly attached to the primary location. I don't think you can push it in any farther than it's supposed to be. In fact I've tried pulling it out of its primary location till the O ring is just on the edge of the metal. If it could securely stay that far out it might reach the other side enough to seal but because it's not secure it'll just slide too far one way or another and lose the seal.

FYI, here's the final result on this. I did need to remove the circular decorative circle. Turned out that once I did this and tightened the cups to the proper specifications the pipe did reach all of the way across, ...just barely enough to seal. I tested this by adding some greese to the O ring, installing, then uninstalling and looking for grease on the other side. Though it does reach, it doesn't sink deep enough to be very confidence building with sealing out, say water, since it is so close to the edge of the cup. But I'm not worried now that I understand the bracket better. Sealing this off here is probably not adding much longevity to the bike, especially if I occasionally uninstall and regrease things. ...which I hope to do. Thanks to everyone her for the help.