How tight for Eccentric Bottom Bracket Screws?

[gearoidmuar]

My chain had become loose and rattly making noise when I stood on pedals. I tightened it yesterday, and it was really easy. What struck me was how loose the screws appeared to be. I've tightened them to what they were. Now, I don't have a torque spanner so quoting Newton Metres to me is pointless, but how tight by feel should they be?

[Fred A-M]

You shouldn't overtighten them - using a bit of loctite I tighten them to the point of having to strain to apply any real significant force - that has been sufficient for me - over do it and you can pierce the EBB shell apparently.    I've found that it's noticeable if one of the bolts begins to become loose because you'll notice a slight clicking in the bottom bracket if pedalling hard.   However, best just make a cursory check every 1,000 miles or couple of months if you want total piece of mind. 

[sbseven]

As you don't want Newton Metres quoted at you, I'd say "reasonably tight".

The Nm figure is useful, even if you haven't got a torque spanner, as you can compare it to other bicycle component torque figures. The manual says 10-17Nm which is certainly achieved with the supplied multi-spanner without any grunting. For comparision, aheadset stem bolts are normally between 5-10Nm ("be careful not to overtighten"), SPD Pedals 35Nm ("pretty tight"), square taper crank bolts between 40-50Nm ("tight").

Shaun

[gearoidmuar]

As you don't want Newton Metres quoted at you, I'd say "reasonably tight".

The Nm figure is useful, even if you haven't got a torque spanner, as you can compare it to other bicycle component torque figures. The manual says 10-17Nm which is certainly achieved with the supplied multi-spanner without any grunting. For comparision, aheadset stem bolts are normally between 5-10Nm ("be careful not to overtighten"), SPD Pedals 35Nm ("pretty tight"), square taper crank bolts between 40-50Nm ("tight").

Shaun

Good explanation. Thanks!

[gearoidmuar]

Well, I tightened them fairly tight, and they came loose, so I tightened them pretty tight, and they came loose, so finally I tightened them good and tight, and they stayed that way!!

How many more "tights" can you name?? 

[expr]

There are a couple of things to think about as to the reason, on the ebb do you have indents that are close to each other, this can allow the screws to loosen. The other contributing factor as you have partly pointed out is "how tight is tight" and to a certain degree this can make the difference between it coming loose or staying tight. what can of course also happen is that the screws are not coming loose but the indents are becoming bigger due to its soft body, this inturn makes you think that the screw has come loose where in fact its the indent in the body that's enlarged. It can become a little daunting tightening the bolt and wondering if the threads are going to give way but they will take quite a bit of force, needless to say i have allready made a contingency plan for mine in as much as i have made new stainless steel (polished) insert holders tig welded to the frame and then made replaceable threaded inserts.


what can sometimes help is once you have made the initial indent with the screw, you can take out the ebb and lightly drill the indent deeper to form a larger area for the screw head to seat into, but not to deep, your allmost making a countersunk finish NOT counterbore. Then use a lighter force when tightening the ebb screws but with a little loctite blue 243, making sure there is no grease on the threads, or it has been suggested to use a tie wire between the two screws to stop then coming loose, / falling out!

Dave.

[Cake]

Tightening the set screws has been a source of some anxiety for me, and if i had the option available i would follow the same route as expr.  Its the strength of the threads in the frame that concerned me - they have never been a snug fit, more on the loose side.

However, after replacing my chain, i went back to the start of the e.b.b. and reused the original indents.  As the indents were already formed the threads in the frame  didn't come under any real force until tightening and it felt more normal.

Whenever the chain needs tensioning i will now use the preformed indents for as long as i can get away with it.  I also used new set screws after the third tensioning to make a more positive seat in the ebb.

And after a ride i just try a finger tightness test on the screws that takes about a nanosecond - they have only been loose once since ownership.  If it happened more often a dab of loctite (as Fred-A-M says) would be employed.

The other long term option i will consider if the threads in the frame go pear shaped (or just before) is to use a frame mounted tensioner and forget that the e.b.b. is fitted.

[expr]

cake, if the threads do go there is another plan that could be used which is tried and trusted, you can replace the threads in the frame with new ones this is a retrofit engineering process that is used many times, one manufacturer called helicoil comes to mind that I have used in the past. It is performed by enlarging the hole with the supplied drill bit and re tapping the threads to suit the new thread insert. These types of fittings are made from hardened stainless and are fitted as standard into softer metals like aluminium to eliminate the chance of pullout.

Dave.

[sbseven]

That's an interesting engineering solution, expr, but I'm wondering a bit why you felt it necessary to go to that trouble in the first place?

Cake, I use a torque wrench and tighten my set screws to 15Nm, within the range in the Thorn manual. 15Nm is not very tight at all on the scale of bike bolts! There is absolutely no chance of threads in a steel frame being stripped or affected by two M8 bolts tightened to 15Nm. The bolts indent the EBB adequately for this torque setting and the EBB doesn't move, so clearly it's not necessary to apply any more force initially.

The set screws may be prone to loosening (although mine don't seem to particularly) because the bottom bracket area is under some torsional stress when you pedal, especially if you spend time out of the saddle 'honking'. Surely the solution is to threadlock the bolts to stop them loosening (or use a small amount of PTFE tape or just tighten them back up regularly) rather than torquing them up further!

It's perhaps a good idea to put as few indentations in the EBB as possible and to reuse the indentations. It might avoid problems later. I'm marking the EBB shell to guide me as to where the indentations are. Somebody told me you can view the indentations by taking the screws out and shining a light into the screw holes whilst adjusting. I seem to be averaging a chain tension every 2000-2500km, so I'm probably going to end up with only about 5-6 well-spaced sets of indentations.

I think people are asking for trouble by torquing up the EBB set screws well beyond the recommended (and quite low) value...

Shaun

[expr]

Shaun,

I am an engineer and have been for the last 21 years, and have seen many threads pulled out in my time when least expecting it as well ! Therefore I have relieved myself of ever having to deal with the problem. I'm not a pessimist by any means but when I see a potential problem that can be given a better outlook then I will change it for the better. I see that its easier  to have a soloution to a problem rather than a problem with a soloution. I think that there are a few people who have experienced the ebb bolts coming loose, so I'm not sure if they are all to do with the incorrect torque being applied or something more sinister is going on. ptfe tape on the treads is one that I was going to suggest like yourself but decided to leave it out, i think it would work ok but it depends how much is put on and if its on the right way, it tends to unwrap itself if applied the wrong way.

Dave.

[sbseven]

I agree with you that threads aren't invulnerable to stripping and that your solution negates all the problems, but I think you'd still be very unlucky to bork a well greased M8 (fine) steel thread of around 10mm length torqued to only 15Nm...

I'm intrigued as to why the EBB set screws do appear to be undoing for a few people, though, as I'm reasonably confident that if you're not using a torque wrench you'd probably be torquing beyond the recommended value anyway.

Some thoughts: Would a slightly smaller bolt tip provide more bite, I wonder? Would packing the space between the bolt head and flange with a filler washer (rubber/resin/leather maybe) stop the unthreading? Should the EBB be pre-indented and hardened?

[gearoidmuar]

The suggestion that my new holes are near the old ones is not correct in my case. They are miles from them. I can easily see both and will studiously avoid going near an old set.

[expr]

Hi Shaun,

a smaller tip would defiantly require less torque to create a larger indent, its the old stiletto and elephant theory, although I think there is some possability in my initial thoughts that the bolts are not coming loose but the ebb body is being forced into the bolts by gravity plus body weight etc and wearing a larger hole in the ebb creating the illusion that the bolts have come loose.

Also i think that at certain points of the ebb movement there is more more chance of movement being
of the ebb within the shell being created IE: the BB shell at 3 O'Clock position looking at the chain side??


I agree with you on the force required to strip the threads would be ordinarily quite substantial and it does have the fine thread in its favour, in as much as it actually has more surface area thread/ thread contact than that of a coarse thread.

Your thoughts on the packing washer are quite usable and would work given the packing washer is slightly elastic to allow it to be compressed etc and to allow for the slight tolerance required in indent depth.

Pre indented I'm not so sure on, this would only allow for specific prefixed adjustment and not real life requirements?

The one thing that i looked at before i changed mine was to put a small M4 grub screw in the side of the threaded boss at 90 deg to the opening therefore creating a locking screw for the M8 fine bolt, but that did exactly what i thought would happen and start to Gaul up the threads on the M8 fine bolt when removing due to the distorsion that the grub screw had caused in the locking process.

I then looked at scrapping the whole ebb adjustment theory and having a wedge type ebb barrel made like those allready fitted to other style tandems etc, but after hearing of some of the horror stories of trying to remove them i gave it a miss and settled for what I have now. I'm sure it would have worked with plenty of grease around it???

I also now put a small rubber boot over the M8 bolt and onto the threaded boss with a zip tie around each boot, this stops the bolts getting water and grit in and helps keep everything clean. I have to admit Ive never experienced the bolts coming loose and do tend to keep them on the looser side after drilling the indends a little deeper and using a little loctite, therefore hopefully negating the chance of having to change the threaded inserts unnecessarily.

I have to agree with cake in as much as the threads that were in my frame before they were removed were on the slack side the same as his. You could wobble the bolt back and to, this is something that goes away if you fit helicoils they always seem to produce nice tight threads and give a better sense of fit.

[terrysmith]

I new here to the EBB, Rohloff Hub chain tensioning issue, but it seems to me that with what I've read ie., "try to use the prior indents" etc,  that a better method of holding the EBB tight can be found on other bikes such as the Santos Travel Master, or the Co Motion.  I've been looking at the Thorn Nomad with the Rohloff hub and these "Set Screws/Bolts" are a problem in my mind.  Or am I making more out of this than need be?

Terry

[julk]

Terry,
Welcome to the forum.

My opinion is - Yes.

The Thorn solution is the least likely to give trouble over the lifetime of the owner or bike.
Just leave the chain to get quite slack and then adjust - no problem!
Julian.