Eccentric Bottom Bracket

[neil_p]

Hi all,

I understand the principle of the Eccentric Bottom Bracket, but can't quite visualise how the adjustment system works with the the normal BB.  I'm guessing the normal BB is inside a cylindrical case which the eccentric screws push up against.

Also, when the EBB is in the low position, why is damage to the BB more likely.  I can see the EBB shell is closer to the bolts, but why is that a problem?

I've seen the diagram on the Thorn Bike Owner Manual on the web, but that only shows the exterior.  Has anyone got an exploded diagram of the EBB so I can see the internal workings?

Thanks.

Neil

[stutho]

The bottom bracket (BB) sits off centre in a cylindrical shell (EBB Shell). The EBB shell can rotate in the frame therefor allows movement of the BB relative to the frame.  The chain tension is adjusted by this movement, when the desired adjustment is achieved the two clamping bolts are tightened against the EBB shell stopping its rotation.  

The EBB shell is solid aluminium and therefor very robust however one side is thinner than the other side (due to the location of the BB).  It is advisable to only clamp into the thicker side.

There is only 4 part to the EBB: a normal BB, the EBB shell and two clamping bolts.  It is a very robust system and VERY easy to adjust. There is no magic going on inside.  

[neil_p]

I'm interested in the newfangled shimano BBs with external bearings, but believe these are incompatible with EBB.  Any news or info on this?

[stutho]

I am curious about external bearings too.  Having said that for a bike that might be taken on expedition I would only accept a square taper BB and cranks - far easier to get a replacement if required. (And probably more robust.).

[PH]

Here's a clear picture on an eccentric without the BB fitted.  Thorn use a different clamping method, but it makes no difference to the way the eccentric works.  As you can see fitting a BB is no different in that than directly in a frame, I can't see there being a problem.

http://ydnar.typepad.com/photos/frankenbike/bb.jpg