Install new EBB

[fmt3]

I'm about to install a new EBB on my old Raven. What is the correct positioning of the EBB on it's initial installation? Looked at some photos of New Raven frames and thin section seems to line up with seat tube. Any suggestions?

Many thanks

[Danneaux]

Yes, the thick part of the eccentric should always be placed directly over the grub screws -- never the thin part.

I've found it easiest to install the new BB with the eccentric itself installed in the frame.

Best,

Dan.

[fmt3]

Thanks Dan.
I've seen the 3 o'clock position mentioned here on the forum. Presumably meaning thickest part at 3 o'clock.
This is a pic of a frame from site. Thickest part would appear to be at 6 o'clock.
Am I missing something?

Many thanks

Dean

[Danneaux]

Apologies for my too-brief response, fmt3.

I should have said, "the thicker part of the eccentric should always be over the grub screws".

So long as you avoid the thinnest part, you should be fine. The reason for all this is the grub screws apply localized pressure and if this comes in the thin part, it can distort the eccentric.

Putting the thickest part if the eccentric at the 3 o'clock position is about the maximum, in my view. If more takeup is needed at that point, it is time to dial back the eccentric, remove a chain link and retension.

If you are reusing your present chain then you will want the eccentric in the position that allows you to properly tension the chain. I allow for 12.7mm or 1/2in of  slack in one run of chain.

For reference, I've attached a couple photos of my Nomad's eccentric when I replaced the original Shimano outboard/external bearing BB with a Phil Wood unit.

As mentioned on the Forum previously, it is nice to align the grub screws with past divots they have created so as to avoid chewing up the eccentric unnecessarily. I can be helpful to invert the bike and remove the screws while using a flashlight to peer inside to see where past divots have come. If you enter the term "eccentric" (no quotes) into the Forum's search engine, you'll see a wealth of past information on proper settings wrt to positioning and chain tension. This topic is apropos to your situation:
http://thorncyclesforum.co.uk/index.php?topic=13038.msg97923#msg97923

If you are fussy about saddle height and positioning as I am, you may also wish to readjust your seatpost and saddle at some point to compensate after adjusting your eccentric.

Best,

Dan.

[leftpoole]

Hello,
Dan has of course written in usual manner, a pretty long piece about this subject.
I think that as an opinion the thickest part of the shell should pretty obviously face towards the front. This means that as the chain stretches (wears) the bottom bracket is moved forwards as the eccentric is turned.
It is just my view of course and in my opinion ask those at Thorn.
My bottom bracket has been adjusted in like manner to my suggestion.
Best regards,
John

[PH]

I find these things more obvious when it's the parts are in front of you rather than a keyboard.
The principle is simple enough, start with the actual BB as far back as possible and always rotate it upwards, clockwise from the drive side.
For those who are sensitive to saddle height and geometry, here's what I do - Once I've set a new chain, move the EBB to the half wear point and make any saddle adjustments.  The throw of an EBB is around 12mm, I would notice being that far from my ideal position, but I don't really notice being 6mm either way.  I have a choice of shoes and clothing that will make that much difference.  When I was really fussy, I'd use a half link and only adjust the EBB 6mm, 3mm each way, but I soon got bored with that.  I still use the half link on the Mercury's half size  EBB, but that's to maximise chain life rather than bike fit.  That mini EBB has been dropped on the current version on the Mercury along with the additional screws, I've no complaints about mine, it was clear what I was getting, but it always seemed a bit pointless.

[Danneaux]

A look at pages 12-14 of the Thorn Bike Owners Manual should clear up any confusion:
http://www.sjscycles.com/thornpdf/ThornBikeOwnerManual2Web.pdf

Best,

Dan.

[fmt3]

Thanks all.
So, I should aim to have the thin part of the EBB around the 2 o’clock position?

Dean

[PH]

Thanks all.
So, I should aim to have the thin part of the EBB around the 2 o’clock position?

Dean

The manual Dan links too above says as close as possible to 3 o'clock,  which as I said is as far back as you can get the BB, ie closest to the hub, so maximum adjustability.
In reality the chainring and sprocket will dictate how close to that position you can get,  you have to put it all together and adjust the chain, do that with the BB moving upwards and the thickest possible bit of  the EBB will always be at the bottom.  All you have to remember is that the BB adjustment is a semi circle and that the BB needs to travel through the top half of the circle.

[fmt3]

Many thanks