eccentric bottom bracket - 10 -17 NM torque

[PH]

It seems to me a poor design, the bolts attempt to fix the curved eccentric against a matching curve on the BB shell.

Don't understand. The BB shell is cylindrical obs, the eccentric is circular where it touches the inside of the BB shell.
https://www.sjscycles.co.uk/bottom-brac ... tour-only/

I don't understand either. Once the screw points have made indents the assembly is solid. As I said I never had an issue, there was certainly no rocking! I have seen some examples where the inserts were chewed up, it has always been from a lack of understanding and being wedded to the idea that they ought to be infinitely adjustable.

[PH]

The BB shell was partially split with 2 strips which tightened on pinch bolts, clamping up on the circumference of the eccentric.

That's how the current Thorn frames are made (Initially with four bolts, then realising that was overkill with two) having used both I prefer it, just easier. Functionally there has been no difference.

Tout Terrain (Possibly others) go one step further and split the entire BB shell. I copied this design on the custom XACD ti frame I had made, that was also faultless for the 7 years before the frame failed elsewhere.

[NickJP]

What a cheap and nasty system for a " prestige brand"

Yet reliable in use.
The wedge type EBB is the prettiest and most expensive, it's also the only type I've had issues with.

We have one tandem using pinch bolts for the eccentric BB:

and one using grub screws where the screw points indent the BB eccentric to hold it in place:

I prefer the pinch bolts, as I can make as small an adjustment as I like to the eccentric. With the grub screws, with adjustments for chain stretch over time, the eccentric winds up with multiple indentations, and when you fit a new chain and have to re-adjust, if the setting is slightly off one of the previous settings, the grub screws tend to find the previous indentation rather than the setting you presently want.

[531colin]

Nick's tandem with the pinch bolts is like my fathers tandem. Transparently obvious how it works, and its the system both Nick and me prefer.
Nick's one with grub screws has 2 grub screws per side, so there is less chance of it rocking because it has 3 points of contact per side, but you still get the indents.

[531colin]

The BB shell was partially split with 2 strips which tightened on pinch bolts, clamping up on the circumference of the eccentric.

That's how the current Thorn frames are made (Initially with four bolts, then realising that was overkill with two) having used both I prefer it, just easier. Functionally there has been no difference.

Tout Terrain (Possibly others) go one step further and split the entire BB shell. I copied this design on the custom XACD ti frame I had made, that was also faultless for the 7 years before the frame failed elsewhere.

So Thorn have seen the light!

[Jdsk]

...
With the grub screws, with adjustments for chain stretch over time, the eccentric winds up with multiple indentations, and when you fit a new chain and have to re-adjust, if the setting is slightly off one of the previous settings, the grub screws tend to find the previous indentation rather than the setting you presently want.

Thankyou, I had wondered about that.

Our Dawes tandems have tangential clamp bolts. They work fine, but I wish that someone had told me how to use the thread to relax the shell to allow the eccentric to turn!

Jonathan

[PH]

With the grub screws, with adjustments for chain stretch over time, the eccentric winds up with multiple indentations, and when you fit a new chain and have to re-adjust, if the setting is slightly off one of the previous settings, the grub screws tend to find the previous indentation rather than the setting you presently want.

I think there's general agreement that we all prefer the pinch bolt type, there's a difference between that and the idea that other systems are cheap and nasty. My experience is with tensioning a chain on a Rohloff rather than a tandem, of which I have zero experience. On a Rohloff there really is no need to make precise adjustment, three positions is all that's required for the throw, it isn't a question of the adjustment finding previous indents, more of choosing to use them. I've seen variations on this, including inserts and shells marked to line them up and pre drilled indents.

[colin54]

Avoid the temptation to adjust too regularly and try and create just a few craters so that you can try and find them next time you replace a chain. Chains can be run very slack. The only time I have had a problem is where two holes joined and the EBB could move slightly causing an irritating click.

Them's wise words. Here's what I found on my second-hand Raven Tour when I first bought it, note the pair of three holes running into each other, eventually it looks like the screws loosened and carved the lovely snail trail towards the bottom of the picture. I replaced it with a fresh unit. The screws that tighten into the eccentric have an extra-fine m8 thread and I've had one come loose since having tightened by feel only. I was chary about over-tightening for fear of stripping the fine thread. I eventually bought a cheap torque wrench which tightened more than my guess-work. Picture of the extra-fine and pointed screw next to a standard M8. The screws would have been in the uppermost of the three contiguous holes when it all came adrift. I think I put on a tiny dab of Loctite thread lock the last time I adjusted it.
I think if the OP tightens the screws enough to make the same diameter indentation as the ones already there as tightened by Thorn from new, that might be a plan (if tightening without a torque-wrench).