Incorrect EBB position - how to fix?

[taraleigh]

Hi,

I just took my Nomad Mk2 to a shop and had a new EBB and shell put in. When I got it back, the eccentric was positioned so that the thinnest part was at the bottom (6'oclock) and the holes were at 12'oclock. I see now in the manual that it says that the screws should never pierce the thinnest part of the eccentric.

Also, the EBB now needs to be rotated clockwise to tighten instead of counterclockwise. Not sure why that is.

Is this an easy fix? I am not located near any shop and had to make a special trip to get my maintenance done.

I have ridden it 65km already in this position and I am hoping I haven't caused any damage.

[WorldTourer]

There is a good chance that your EBB is permanently damaged. Tightening the screws at the thinnest part will destroy the bottom-bracket threads. When I was a novice Nomad owner, I made this mistake, and what happened is that the bottom bracket started to unscrew itself from the shell as I cycled. Only the purchase of a new EBB shell from SJS gave me a working bike again.

Sadly, many local bike shops have never seen an EBB, and you really can’t trust them to properly do maintenance on one. At best, you can only emphasize beforehand that the screws need to go into the thick part, but this message might get lost as the shop clerk hands the bike over to one of his mechanics.

[macspud]

If the holes/bolts were at ninety degrees to the thinnest part you should get away with turning the EBB the correct way up.   

[taraleigh]

If the holes/bolts were at ninety degrees to the thinnest part you should get away with turning the EBB the correct way up.   

Ok and this can be done with the cranks attached? The position isn't exactly 12:00..more like 11:50-11:55

[JohnR]

See pages 13-14 of the thorn bicycle owner's manual http://www.sjscycles.com/thornpdf/ThornBikeOwnerManual2Web.pdf . My Mercury was supplies with the two-pin tool for doing the rotation but with another bicycle with EBB I found I could do the rotating by putting an Allan key in one of the holes and pushing it round with the crank. If you rotate such that the thin part of the EBB shell is nearest the back wheel then you won't be fighting the chain tension. There will be a vertical mirror image position for the EBB position which gives the same chain tension.

[PH]

There will be a vertical mirror image position for the EBB position which gives the same chain tension.

This is the important part, just keep turning the EBB inserttill you have the same chain tension with the thicker part at the bottom.  Doesn't matter which direction you turn it, in 180 degrees you'll be about right. Might be easier to take the chain off to do it, then reattach for the last bit of adjustment.
I can see how the BB itself could be damaged, but I imagine it would need considerable force to do so, more than required to hold the EBB. To be sure of this, you could remove the BB and check the threads, but if it felt OK I wouldn't bother.

[taraleigh]

I ended up rotating the shell counterclockwise until it got to optimal chain tension, which put the holes right around 6:00 and they were at around 12:00 before. I am guessing that they suggest to have the thinnest part of the eccentric at 3:00 (holes at 9:00) so that it gives the most adjustment?

With the thinnest part now at 12:00 (holes at 6:00) will it shorten the range of adjustment before you need to take out a link or two and start over?

[JohnR]

I've found that very little EBB movement is needed to take up any slack in the chain, besides which Rohloff and Thorn recommend a fairly slack chain (see the owners manual).