An eccentric bottom bracket (EBB) is one that allows you to move the normal bottom bracket, which is screwed into the EBB, forward or back so as to tighten or loosen the chain or belt. After you reach the desired tightness it is necessary to fix or lock the EBB in place. You can do this with wedges that slide up and down ramps and bear against the inside of the frame. Vivente Rohloff bikes have a Genio unit (pictured below) and use a 5mm hex key. Torque of 8-10Nm is sufficient to lock it in place.
Loosening the EBB Unit
Use the long hex key with the copper pipe extender as in the picture below. To unlock the position the hex-head just turn it counter clockwise. After one-two turns you notice there is a point where resistance rises. This is where the wedges are being dislodged. Your unit is not yet free to rotate until you turn another few turns, through this resistance. Now, providing there is sufficient grease on all of the internal surfaces, the unit will be free to move sideways or to be rotated slightly in each direction.
Setting Correct Belt Tension
Correct tension is important. However, carbon belts, unlike chains, do not stretch or elongate so only lose their tension over a very long time as slight sprocket and belt deterioration develops. With a life expectancy of 25-30,000 km this is indeed a very long time. A new Vivente bike comes with this preset and you are unlikely to need to touch it. If you do ever need to there are two things to know.
- how to rotate the EBB unit in the frame, and
- how to measure the belt tension before tightening.
Once you have loosened the screw, you should be able to freely rotate the EBB unit in the frame. You might need to coat the EBB with grease if it’s not rotating. Due to the range of positions and directions possible It is hard to make one tool to rotate it. Pin spanners can be used as in the picture below but it is not easy to get sufficient purchase with them. If you’re stuck without tools you can use zip ties. See the picture below for an example of the zip tie method.
Another very simple method is to hold the hex key firmly and turn the crank to get leverage against it, with some cloth between the crank and the tool. To measure the tension Gates makes the Krikit Gauge, small enough to fit in the tool bag. It sits on top of the belt and allows for single-finger tension testing through the click of a button. There is also a phone app that you can download to check you have achieved the recommended range of 35-50 Hz (Apple, Android).