Cycling UK Forum

adjusting the tension on my chain which because it has a rohloff gear has eccentric bottom bracket

the thorn booklet, it's a thorn raven says tighten the eccentric bottom bracket screws at between 10-17 Newton meters of torque, just wondering what that feels like as i don'y have a torque meter, just a spanner- is it not too tight????

What's the lever length of the tool that you intend to use?

Jonathan

abut 6 inches

6" = 0.152 m

12 Nm torque at 0.152 m is 78.7 N force.

78.7 N is the weight of 8.03 kg.

So if you hang a mass of 8kg on that tool with it horizontal it will exert a torque of 12 Nm.

(Please can someone check.)

Jonathan

I foot pounds is a 450g tin of beans at 12 inches. Simples
15 ft lbs is roughly 8 kgs at 12 inches and about 12nm.
This is double jonathans figures so one of us is wrong.

If it is one of the EBBs that is held ion place by two bolts that indent the surface I'd say pretty tight. I have one and as long as you have it correctly aligned so that you are bolting into a thick section it will be fine, that's a solid chunk of aluminium. It would be hard to damage the BB. 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.

beeb wrote: ↑2 Aug 2023, 2:12pm adjusting the tension on my chain which because it has a rohloff gear has eccentric bottom bracket

the thorn booklet, it's a thorn raven says tighten the eccentric bottom bracket screws at between 10-17 Newton meters of torque, just wondering what that feels like as i don'y have a torque meter, just a spanner- is it not too tight????

Torque wrench £17 on Amazon you can always send it back if you don't like it !

This is double jonathans figures so one of us is wrong.

12Nm is a tad under 9ft lbs

10Nm isn't much. Gripping a spanner in the middle with your whole fist and using a wrist-twist is about it. Putting your fist on the far end and putting your weight behind it is too much. Works for me, but I'd use a torque wrench if it's critical

geocycle wrote: ↑2 Aug 2023, 3:34pm If it is one of the EBBs that is held ion place by two bolts that indent the surface I'd say pretty tight. I have one and as long as you have it correctly aligned so that you are bolting into a thick section it will be fine, that's a solid chunk of aluminium. It would be hard to damage the BB. 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.

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

As tight as you would do the expander bolt of a quill stem, if that means anything. Normal hand tightness with a 6mm allen key of standard length.

thanks all

The intention on first tightening in that position is for the cone of the screw to make in indent. Then for subsequent adjustments to that position to use the same ones. If the indents are already there, re-use them, which just requires the screw to be pinched up enough to not come lose. Worst thing you can do is adjust it in such a way as the new indent is so close to an existing one it slips into it. There is no need, an IGH's chain tension doesn't need to be precise.
One way to ensure you're either going into fresh metal, or an existing indent, is to remove one screw completely and shine a torch in.
The EBB inserts are cheap enough to replace if it's chewed up.
I had a Raven for 7 years, several chains, one EBB insert, never sliped or gave any other prolem, never saw a torque wrench. That the reccommendation is 10-17 ought to tell you it doesn't need to be exact.

531colin wrote: ↑3 Aug 2023, 7:43am 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.

PH wrote: ↑3 Aug 2023, 11:01pm

531colin wrote: ↑3 Aug 2023, 7:43am 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.

I don't have a huge amount of experience, but the 2 bolt type is the only one i have had problems with, admittedly on machines of unknown history on a blind tandeming outfit.
It seems to me a poor design, the bolts attempt to fix the curved eccentric against a matching curve on the BB shell. If the shell had 2 ridges opposite the bolts you would then get 3 points of contact which can't rock, like a milking stool.

Never played with an internal wedge one .....I expect it has the same basic snag as above, trying to fix against a curve rather than points?

The best system should be familiar, continuously adjustable, and obvious how it works at a glance. That goes to my fathers tandem, a "Harry Rensch" brand of Paris Cycles, most known for the "Galibier" frame. The BB shell was partially split with 2 strips which tightened on pinch bolts, clamping up on the circumference of the eccentric. The original eccentric had a Williams or Bayliss Wiley bearing where the cups fitted a threaded sleeve, maybe a modification to get rid of Chater Lea oversize BB bearings? I replaced it with an ali. eccentric and standard cups....Andrew Hague is a name which comes to mind, for the eccentric and ali. carriers at the time?

My old pre war (BSA?) tandem had a rather less obvious arrangement. 2 tunnels on the BB shell (orientated front to back) contained 2 bolts which tightened pairs of tapered collets (?) against the eccentric. Once you worked out how it worked, it was faultless.

531colin wrote: ↑4 Aug 2023, 12:55pm 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/

Have to say never had a problem with mine, and you can tighten those slotted screws with a spoon if necessary until you can find a mechanic and borrow a 14mm spanner (might be 15mm).