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I have a bike powered by a Gates belt-drive and a Shimano Alfine 11. It also has an eccentric bottom bracket to adjust the tension on the belt drive, and a SRAM GXP bottom bracket.

The other day, just by following videos on Youtube since no other help was available, I tried replacing the old bottom bracket with a new one… and it looks like I ruined the threading on the drive side of the eccentric BB: I can hand-tighten it, but when tightening it further with a wrench, it loosens again, ie. I can never tighten if fully. It looks like I'll have to buy a new eccentric bottom bracket :-/

The issue: How to identify the brand + model of that eccentric BB without taking it out (I'll need to ride it to a workshop to fix it)? There's nothing written on the sides, short of L/R:

enter image description here

Also, while I wait for a new eccentric BB, I was thinking of applying some medium-strength threadlock in the hope that the drive-side bearing won't move. What do you think?

Thank you.

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Edit: I cut the derailleur + hydraulic brake hoses that run through the EBB, and pulled the EBB. It's just a cheap plastic part; According to the bike manufacturer, it's a Prime Aero from a company in Taiwan.

Anybody knows where to get a replacement, with the opening in the middle to let hoses through?enter image description here

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  • Think of the eccentric as an adapter between the bottom bracket and the frame. – Criggie Aug 23 '16 at 20:00
  • Finding the exact replacement in plastic at only 67g seems hopeless. Looks like the closer alternative is in aluminum at around $£€30 – OverTheRainbow Aug 25 '16 at 15:59
  • There are two ways I can think of that could conceivably get you a replacement. One is figure out another bike that has the same part and go to a dealer for that brand, who can then call them up and see if they have one they can sell you. The other is email the Taiwanese manufacturer directly: wheelgiant.com.tw/publication/tbs/…. They might see the predicament you're in and help you out. But if you can find an aluminum one that will do the same thing, I think you should go for it. – Nathan Knutson Aug 25 '16 at 16:15
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Pulling an eccentric out that's not stuck is usually pretty straightforward once you've gotten the cranks off. If you want to find out the brand and model info (which might not actually be that useful anyway), that's probably the only place you'll find it, if it's there. But, if you're going to try to source a new eccentric yourself, you really should pull it anyway to get an exact measurement of the shell's inside diameter.

If this is any kind of mainstream bike manufacturer, where I would start here is calling them up and seeing if they have a replacement they can send to either you or a dealer. If so, that path is going to be about a million times easier than anything else, and probably cheaper.

I'll also mention that the framebuilding suppliers like Nova are the main source I've seen for more simple 1-piece eccentrics like you appear to have. Most of what you'll find elsewhere are the premium ones like Bushnell, Phil, and Niner.

As for the Loctite idea, with GXP there's not really any place for it to move to. I would never recommend riding on a loose cup, but people do all the time, with the main consequence being noise and play in the cranks.

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  • Thanks. It's indeed the eccentric BB itself which is damaged: Neither the orignal BB nor the new one I bought (silver) can be wrench-tightened. Derby, the original manufacturer in Germany didn't want to bother helping me with that item. Looks like I'll have to get the right tool, remove it, and try to find a replacement. – OverTheRainbow Aug 24 '16 at 19:23
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First off, all you will need to buy is a new BB. The eccentric shell is not an integral piece of the BB. It is there to adjust the tension on the belt.

The part you damaged is the BB cup. You are in good company as many people have done this :) In the future, after the cranks are removed, the solution to removing a BB cup is as follows: Using the appropriate wrench (that is, it has the same number of notches as the BB cup) place a thin piece of cloth (like a t shirt piece) over the bottom bracket. Wiggle the BB wrench into the grooves on the now covered cup. Turn in the proper direction to loosen, which depends on the side you are working on. The shirt removes any slack in the fit between the BB and wrench. You can try this on your damaged BB to tighten it.

As far as the BB goes, it is very likely a SRAM GXP BB. They are 25 bucks or so. Look up the crankset name and google what BB goes with it. Most of the GXP's (and I do mean most ) are 24mm if I remember correctly. Good luck!

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    If the threads of the eccentric are damaged, then the OP probably needs a new eccentric. – Nathan Knutson Aug 23 '16 at 17:11
  • Does the OP indicate the threads of the eccentric are damaged? Or does he indicate the BB cups are damaged? Eccentrics are pricey, and I imagine that the aluminum cups used in the BB are going to strip well before the threads of the eccentric are damaged. The fact that the cup will thread in but slip upon torque suggests a BB cup problem. – user26705 Aug 24 '16 at 14:11
  • They say "it looks like I ruined the threading on the drive side of the eccentric BB." They're presumably both aluminum parts. – Nathan Knutson Aug 24 '16 at 16:01
  • There is a lot to be desired in consistent terminology in this post. And both of them being aluminum thread would be poor design. You would likely have a aluminum eccentric with a harder metal insert for the BB to screw into. – user26705 Aug 24 '16 at 20:01
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The other option available to the OP is to buy a helicoil kit to fix the damaged threads or switch to a square taper BB to which there are special BBs available to run on a damaged thread.

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  • Where does the OP state that the eccentric is damaged? The cups are weak aluminum and by design should strip first. But yes, an excellent idea. But those are pretty big holes to tap at home. He should take it to the LBS and let them do it. – user26705 Aug 24 '16 at 14:14

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