GXP BB service
 

I posted this twice in the "Single Speed & Fixed Gear" section a few days ago and it was closed. I figured that it would be the appropriate section since the topic of concern deals with a track crankset and BB. I didn't receive any messages and it wasn't moved to another section so I don't know what's up with that. I used the "contact us" section and got no reply.

Anyway, I bought a Sram Omnium crankset to upgrade from my Sugino XD. I noticed that the GXP BB was making a crunchy sound when I turn the crank. I removed the crank and the sound occurs when I turn the dust cap on the drive side. Does the dust cap come off? I don't want to try taking it off and end up damaging it. Thanks

New or used? generally, external BB's are not user serviceable, till you get to high end models like Hope, Phil, or Chris King.

If used, replace with a new one

If new (or used) was the frame prepped (faced) before install?

Brand new. I'm not familiar with the term "faced" I just greased the threads and installed, that's it.

BB facing, in very simple terms, is making sure that the 2 faces of the BB shell are parallel, this is a LBS job, due to the cost of the tools needed, This is only applicable on threaded BB shells (like yours).

It's not essential, but does mean that you have a good base to start with. For the crunching, am wondering, does this actually affect the ride? external BB's (HT2, GXP etc) have more drag than cartridge BB (like with your previous crank) when not under load (i.e in a stand) but when your riding it, it won't be noticeable.

The dust cap on the drive side should be a plastic bushing/dust cap combo and it comes out fairly easily. It sometimes comes out with the crank spindle, when you remove the crank.

Maybe what I'm referring to is not a dust cap. I'm talking about the cap that spins, I'm pretty sure it's on the drive side. It has 2, or 3 dots on it, I thought that would be an indication of the type of tool you would need in order to pull it out, but I just want to make sure that it comes off so that I don't end up damaging it. I know this is the issue because I heard the sound, took it all out and turned it with my fingers and it made the same sound.

This is a GXP bottom bracket with the dust covers removed. Drive side is on the right.

You may not be able to avoid just buying new replacements.

Just pop the snap-ring you see on the top (might need some careful prying with a very small flat screwdriver while keeping the other end with another object) and pop the bearings out. Measure OD and ID and width and get proper bearings from SKF.. but you will find some odd dimensions like 24ID and 22ID and standard bearings have 25mm ID.

Here is a neat adapter ready-made to make GXP use standard industrial bearings: http://www.enduroforkseals.com/siteb...p_by_rwc_f.pdf

But it will cost you way more than just changing the BB with a new one.
Of course if you have the tools (i.e. - lathe) and knowledge you can make a bushing of your own to make use of standard size bearings and change them cheaply and (WAY) more durable.

It's the one on the right. Should I force it out by hand or is there a proper way to remove it?

Good info, I saved the document for future reference. Do you think it's worth it? Would it be just as durable as a higher end BB?

If the faces of the BB shell aren't parallel, you'll have problems like you're describing because the cups will be crooked and bind on the spindle.

If the BB is new, there is no reason to start tearing apart the bearings before you rule out more obvious stuff. When you turn the bearings with your fingers, do the actually sound like they ares making noises, or only after the crank is installed?


I looked at your history and don't see any closed threads. Do you mean it just disappeared?

I'd say that bearing making is a huge industry for very high rated applications that exceeds any type of loads a bike will ever have. More than that, industrial bearings have the ratings and characteristic carefully tested and written and certified. So my opinion is yes! Namebrand (SKF, FA.G, and others) bearings is the way to go in any applications that require bearings. And possibly a lot cheaper. Bikeparts are VERY inflated in price due being bike-specific but there is little transparency in what a bike part can withstand with testing and certifications.. so whenever possible, I go for the real deal with all papers attached (for bearings, oils, grease, chains, bolts etc)

Sure there might be a weight difference.. because bikes have low power, low speed, low loads, some bike parts are really flimsy but they do their job.. like ceramic bearings and others. For me, the added weight for a steel bearing vs ceramic bearing is a non-issue (it can be in a racing environment but that is rarely the case)

You should be able to pop it out by hand. There is a very small ridge on the back of the plastic bushing that keeps it in the bearing bore. You can pop it out with a screwdriver blade, if finger pressure doesn't do it. There is a rubber lip seal on the bearing(gray seal with dirt under it in the picture) that is supposed to prevent dirt from getting into the bearing. Dirt will accumulate under the lip, as it is in my photo, and cause the crunching sound you hear. You can carefully lift that lip seal and wipe the dirt from under it.

Typically the non-drive side bearing will go bad before the drive side in a GXP bottom bracket, due to the design using that bearing to prevent lateral movement. If either bearing feels rough or has play, when turning by hand, the bottom bracket should to be replaced

Here's an update on the BB situation. I found out what was causing the sound/ play and it was a very simple fix. All I had to do was remove the white paste, clean out the inside with WD40 and a rag, and regrease. I should mention that the play accrued every time it passes by this spot:

http://i78.photobucket.com/albums/j8...tombracket.jpg

Maybe the paste wasn't allowing it to turn smoothly, but either way the sound it gone and I'm happy.