Author Topic: Thorn Double-Ended Raven Eccentric-adjusting Tool  (Read 3614 times)


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Thorn Double-Ended Raven Eccentric-adjusting Tool
« on: April 17, 2008, 11:29:43 PM »
Hi all

If you did use this particular tool on your Raven Tour BB, can you describe
how to use it correctly (to tighten your chain), please.
A picture would be great!



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Re: Thorn Double-Ended Raven Eccentric-adjusting Tool
« Reply #1 on: April 18, 2008, 09:17:29 AM »

I have used this tool, it is very easy.  The thing to keep in mind is that the EBB (excentric bottom bracket) needs to rotate inside its shell.  As the EBB rotates it moves the BB (bottom bracket) closer to or further away from the rear axel hence taking up any slack in the chain. 

You need to remove the grub screws from the bottom of the EBB shell that hold the EBB in place first.

To use the tool you hook it into one of the notches on the outside of the EBB.  Looking at the picture you posted it is the part on the extreme right that hooks into a notch on the EBB.  The tool itself is aligned so the curve (seen on the right of your picture) meets with the curve of the EBB.  The tool is aligned with the frame of the bike.  I.e. looking from above you see the thin edge of the tool.  Looking from the side you see the full outline of the tool.  With the tool in this position you only need to apply a very gentle pressure to rotate the EBB.

There are a couple of things to keep in mind. 

First with the grub screws removed it is easy to move the EBB sideways and you need to be careful make sure the EBB stays centred inside its shell.  By centred I mean if you are sitting on the saddle in the normal riding position you want the EBB centred in a left Ė right sense, an extreme example would be having the EBB half out of its shell to one side of the bike.  If you get this wrong the front chain ring will not be aligned with the rear sprocket and the chain run will not be straight.  Secondly you also need to keep the thick part of the EBB downwards.  If the thin part ends up next to the grub screws you can do some damage to the BB.  Thornís documentation on adjusting chain tension makes special mention of this point but not the first point.

In actual fact you donít really need this tool at all.  Over Easter my chain was coming off because it was too loose and at camp one night I adjusted the chain tension using only my hands to rotate the EBB inside its shell.  I didnít take the tool with me on that tour and after this experience I see no real need to use the tool again.  As long as it is aligned correctly when you tighten the grub screws you will be fine.



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Re: Thorn Double-Ended Raven Eccentric-adjusting Tool
« Reply #2 on: April 18, 2008, 09:42:13 AM »
Be aware that eventually the eccentric can seize within the BB shell so that even with the two locking bolts completely removed it will be very difficult to rotate the eccentric. I ended up bending the tool trying to do this. Eventually got it free with lots of WD40 and a big rubber mallet! Worth checking this regularly I think.


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Re: Thorn Double-Ended Raven Eccentric-adjusting Tool
« Reply #3 on: April 18, 2008, 01:07:28 PM »
Just to add to pdamm comments.  I have one of these tools in my toolbox but normally I set the rotation / chain tension by hand rotating the EBB.  Personally I find it quicker and even easer to do it this way that to use the spanner! 

One positive feature of the spanner is that it is that it is a little bit shorter than the average 15mm spanner and therefore has a little less leverage.  This is a good thing as you don't need too much torque on the EBB bolts.

Adjusting the EBB is VERY easy.  Much easer than it looks!  I would say that it is about as difficult as setting the height on a seat post.   Everyone things it is difficult until they have adjusted it.

Rules for adjusting the EBB
1. Make sure the thicker part of the EBB is closer to the bottom than the top of the BB shell.
2. Don't mussel the bolts
3. Don't over tighten the chain.  Better the chain is slightly loose than too tight
4. Put some copper grease on the EBB / BB shell interface (to avoid the EBB seizing) 

The job takes less than three minuets, once you are practiced.
For some more info look on pages 10 and 11 of the manual   


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Re: Thorn Double-Ended Raven Eccentric-adjusting Tool
« Reply #4 on: April 18, 2008, 03:53:55 PM »
Thank you all for your excellent comments!
There is nothing better than ... hands-on experience.

Peter, many thanks for your step by step description!!
I truly appreciate this as I was nervous about doing this
right. Great help, and much appreciated!