Bosch CX gen 4 chainring nut

[Gyre]

Hey guys, I've got a dumb question on the Bosch lockring nut. Since the threading is CCW and the spindle wants to spin freely clockwise, is there any practical way to loosen the nut without chain tension holding the chainring in place?

 

[Mikerb]

chain whip

 

[MrPeaski]

Most practical way is to leave the chain on, but if for some reason you can't then a chain whip as @Mikerb says.

To fit it back on you can use the opposite crank arm to hold things still while you tighten things up.

I've also found that using the flats (on the tool I linked to) is steadier than the 1/2" drive hole.

 

[Gyre]

Ok, good to know. Have to see if I can still find my old chain whip - haven't used the thing in at least ten years.

 

[MrPeaski]

I mentioned in my post #88 about the lack of an 'O' ring on mine that a lot of other users spoke of.
E-Thirteen recommend leaving it out on their direct mount rings as described here...

The o-ring found between the chainring and lockring on Bosch G4 systems is missing with my e*spec ring. Is that correct?

We recommend removing/not using the o-ring which sits between chainring and the lockring when assembled with our direct mount ring. BOSCH G4 motor assemblies come with BOSCH Supplied lockrings a...

support.ethirteen.com

I've noticed that on non E-Thirteen rings and spiders that there is a slight indentation, presumably this prevents the 'O' ring from bunching

 

[Gyre]

I mentioned in my post #88 about the lack of an 'O' ring on mine that a lot of other users spoke of.
E-Thirteen recommend leaving it out on their direct mount rings as described here...

The o-ring found between the chainring and lockring on Bosch G4 systems is missing with my e*spec ring. Is that correct?

We recommend removing/not using the o-ring which sits between chainring and the lockring when assembled with our direct mount ring. BOSCH G4 motor assemblies come with BOSCH Supplied lockrings a...

support.ethirteen.com

I've noticed that on non E-Thirteen rings and spiders that there is a slight indentation, presumably this prevents the 'O' ring from bunching

That's interesting and a little confusing. Should the bulletin be generally applicable (seems so, but not 100% sure) and regardless, what problem was the o-ring trying to solve?

The other odd thing is that it turns out my Orbea Wild's chainring might not be an ethirteen ring at all. Everything else related to the crank, including the chain guide, is all ethirteen, but the chainring is actually just a spider with (presumably 104bcd) chainring bolts. When I was cleaning it, I found the o-ring buried under some caked on crud. Time to decide whether to transfer it to the new FSA spider I just installed.

 

[MrPeaski]

It looks like FSA do 3 Gen 4 spiders, 2 of which have a slight indent around the spline teeth.

Here FSA BOSCH gen4 alloy spider
Here FSA BOSCH gen4 1x12 spider
and here FSA BOSCH gen4 steel spider

If you have the first one as linked, I'd leave the o-ring out as it looks the same as the E-Thirteen ring.
For the other 2 I'd use the o-ring.

 

[Mikerb]

I presume the role of the "O" ring is to provide a water/dust seal to protect the splines of the shaft. Installed with some grease it should not then bind when the locknut is tightened.

 

[millemille]

Having had the lock ring on my Bosch motored Focus Sam2 come loose I think the theories being punted around in this thread are ignoring the principle of Occams razor.

The lock ring is thin for the thread diameter, so there are a limited number of engaged female threads.

The lock ring is made of aluminium, so the clamping force that can be exerted through the threads is low.

The output shaft of the motor is splined as are the male threads, so the cumulative length of engaged threads is reduced and cannot tolerate significant clamping force being exerted through them.

The lock nut is operating in a water and/or dirt filled, vibration rich, environment.

It's a recipe for coming undone.

Thoroughly clean all of the threads and output shaft and the chain ring clamped faces and the lock ring with a nylon brush and a solvent, apply loctite 243 (or similar medium strength threadlock) to the female threads, tighten to 30Nm with the proper tool and a calibrated torque wrench, apply torqueseal witness mark and check the torqueseal regularly.

 

[HORSPWR]

Occams razor.

You do know what this is yeah?
No more theories should be put forward than necessary but in your explanation above you've got twice as many explanations as any other poster

 

[Mikerb]

You do know what this is yeah?
No more theories should be put forward than necessary but in your explanation above you've got twice as many explanations as any other poster

On the contrary he puts forward only one hypothesis..........albeit he details several aspects of it.........namely that nut and thread have very little surface contact hence the need for loctite. He does therefore adhere to the rules of parsimony as should every good engineer

 

[marks123]

Spent time looking for the tool needed to remove the chainring nut as shown in the first picture of this thread.
The 'official' bosch part is priced between £30-£45.
There is an alternative at £15, that I've got and used; IceToolz BB Tool, 8-notch, Shimano / ISIS Drive, #11D3
I think any ISIS 8 notch tool will work that thas the same spec.

 

[Zaskar20]

I think any ISIS 8 notch tool will work that thas the same spec.

Yep
I used this.
I’m really not sure what the o-ring is for? I don’t think it’s a seal to protect the splines on the drive and chainring. I think the lock ring itself is enough protection, when tightened.
What is the consensus of opinion? Are we refitting without after it’s come loose?
Unfortunately it happened to me today when riding.

 

[Philly G]

I’m really not sure what the o-ring is for?
What is the consensus of opinion? Are we refitting without after it’s come loose?

I didn't refit mine. It seems impossible to tighten the lockring up to specified torque without the o-ring bunching and breaking. As I recall I found the original o-ring already broken, presumably as assembled when the bike was new

 

[Mikerb]

I didn't refit mine. It seems impossible to tighten the lockring up to specified torque without the o-ring bunching and breaking. As I recall I found the original o-ring already broken, presumably as assembled when the bike was new

I suspect there is confusion here when fitting a spider or a direct mount chainwheel, depending whether either is an original Bosch component/ Bosch specified component or 3rd party. The O ring would provide a seal but cannot be used if the component does not include a slight recess/chamfer for it to locate.

 

[Philly G]

I suspect there is confusion here when fitting a spider or a direct mount chainwheel, depending whether either is an original Bosch component/ Bosch specified component or 3rd party. The O ring would provide a seal but cannot be used if the component does not include a slight recess/chamfer for it to locate.

Some people have mentioned a recess for the o-ring, but my bike was fitted with an e-thirteen ring as new, with no machined recess for the o-ring. Seems strange that a ring designed for use with the Bosch gen 4 would not have the recess. I bought a packet of replacement o-rings from a local seals & bearings specialist, but I quickly gave up trying to fit one

 

[Zaskar20]

Some have said the o-ring is a seal.
This is my Hope E chainring when fitting, it clearly has the recess for the rubber ring.
If one uses loctite or grease on those threads (and have greased the spline and chainring before hand), then when the lockring is fitted, nothing is getting onto those splines!

 

[Mikerb]

Some have said the o-ring is a seal.
This is my Hope E chainring when fitting, it clearly has the recess for the rubber ring.
If one uses loctite or grease on those threads (and have greased the spline and chainring before hand), then when the lockring is fitted, nothing is getting onto those splines!
View attachment 80519

Design variations can of course happen when 3rd party suppliers see an opportunity to offer replacement parts. I wonder if some (clearly not Hope) expect customers to buy their lock ring rather than use the original.....a lock ring that has an o ring recess as opposed to the chainwheel providing the recess.
It is certainly preferable to fit an o ring since the lock ring threads onto a splined/castellated spindle which could lead to corrosion.

 

[Zaskar20]

It is certainly preferable to fit an o ring since the lock ring threads onto a splined/castellated spindle which could lead to corrosion.

But in front of the o-ring (and seal) are the splines that are threaded. Much more vulnerable and delicate to any corrosion that may occur that would, in turn, damage the threaded section.

 

[Mikerb]

But in front of the o-ring (and seal) are the splines that are threaded. Much more vulnerable and delicate to any corrosion that may occur that would, in turn, damage the threaded section.

it is those threaded splines the o ring is designed to protect. If you look at the lock ring when threaded on there is a complete face to face mating around its outer perimeter which prevents water and dirt entering from the crank side ( a little grease would also help here). The o ring sits between the lock ring and chainwheel to seal that end of the threaded spline.

 

[Trantor]

I come back to the topic
TECH NERD ALERT: very long and boring post ?

So, the lockring is threaded ccw. We must take into consideration that these components are designed in such a way that their own inertia acts in favor of tightening.

Let me explain and try to analyze the phenomenon.

Working with such a component, the designer determines the direction of the thread on the basis of the direction of the main stress, which will generate a reaction of the component itself (given by its own inertia) in the opposite direction.
In a system with a spider and its lockring, if the system itself forces the component to turn clockwise, its own inertia will generate an opposite, counterclockwise reaction.
The spider (of course) turns clockwise when pedaling.
I can assume (and I want to clarify it, mine are assumptions as a "nerd" designer) that the Bosch designers have taken into account the accelerations impressed by the rider (raises, starts, etc ...) to the chainring via the pedals, action reinforced by the motor also. Then we have the motor shaft that lets the spider move in a CLOCKWISE direction, dragging the lockring with it, making it snap in the same direction; the lockring is therefore forced to sudden start rotating clockwise. Its inertial reaction will generate an anti-clockwise force (i.e. the inertia of the lockring will tend to oppose the movement that was imposed by the spider, making it rotate counterclockwise). All this is represented in the image below.
Blue disk = spider + chainring
Orange disk = lockring
Blue arrow = rotation force impressed by the spider
Orange arrow = lockring intertial reaction

View attachment 33692

With this consideration, I agree with the Bosch designers: the ccw thread is a correct choice because its inertia works to tighten the lockring threaded connection with the spider.

Off-road, however, there is another stress that can become much more predominant: the kick-back generated by the rear suspension.
The stresses that comes from the rear swingarm in a high speed descent on rockgarden or woods create a reverse chain pull force that pulls the chainring back. These stresses are very impulsive, therefore they create a very strong acceleration (in short, a sudden jerk) that works in the OPPOSITE direction given by pedaling action. The consequence is that the inertia of the lockring works this time in reverse, leading it to unscrew.
It makes me believe (I repeat, they are my assumptions) that these stresses are more violent and above all much more frequent in AM, Freeride, Enduro, etc ... compared to those of pedaling (in Ednuro, AM, freeride, etc .. we're used to pedal quiet till the top then descend "full throttle"). We will therefore have a lockring exposed to a reverse stress, the inertia of which will then push it clockwise, thus tending to unscrew it. Jerk, after jerk, after jerk, the lockring becomes loose.

Having said that, were the Bosch designers wrong? NO. They simply imagined that most of the users with Gen4 will do easy and little off-road rides; in this case, I consider the choice correct.

Based on this, I tried to invent a solution to substantially prevent the lockring from moving clockwise because of the kickback
First, a small 2mm hole

View attachment 33693

... then a tap of a grinding wheel to create a small "pocket" on the inner face

View attachment 33694
View attachment 33695

... and then a nice band of safety iron wire. And since security is never too much, even a bit of threadlocker.

View attachment 33696

Now I just have to screw the ring nut again and practice the safety tie using one of the spider spokes. In this way the lockring is prevented to rotate cw (the one that causes the ring nut to be unscrewed) by the wire. It is the same system that I used on the motorbike on the track, where oil caps, brake screws and other components that could be unscrewed had to have the safety tie for regulation.

View attachment 33697
View attachment 33698
View attachment 33700

Unfortunately, job agenda and bad weather do not allow me to perform tests
I'll come back to you in the next weeks with the first feedbacks from the field

I'm having the same issue on the same ebike right now. I had to replace the rear derailleur cable so I removed the chainring . I re-installed it with a proper torque wrench (30 Nm as written on the chainring nut) but it loosen soon after the first 10-15 km of riding. The thread lock is a valid solution ? I also noted that the factory installed chainring is very close to the rear stay and it is very likely to wear the rear stay after a little deformation as happened to me. Is it possible to install a spacer between the chainring and the motor ?

Dr.Ergal I think I met you some years ago in a motorbike forum (hondapeople and quellidellala). Do you remember ?

Thanks in advance

 

[Zaskar20]

I'm having the same issue on the same ebike right now. I had to replace the rear derailleur cable so I removed the chainring . I re-installed it with a proper torque wrench (30 Nm as written on the chainring nut) but it loosen soon after the first 10-15 km of riding. The thread lock is a valid solution ? I also noted that the factory installed chainring is very close to the rear stay and it is very likely to wear the rear stay after a little deformation as happened to me. Is it possible to install a spacer between the chainring and the motor ?

Dr.Ergal I think I met you some years ago in a motorbike forum (hondapeople and quellidellala). Do you remember ?

Thanks in advance

It is possible to add spacer, see my post Cannondale Habit & Moterra Ai Offset - EMTB Forums
It did come undone initially with the rubber o-ring, so I left that off and used blue loctite. It has stayed solid since (and it comes undone easily enough when you want to take it off again)

 

[Trantor]

Great! So you used a carbon spacer to adjust the clearance ?

 

[Zaskar20]

Great! So you used a carbon spacer to adjust the clearance ?

Yep

 

[Philly G]

Yep

Is that a headset spacer?

 

[Zaskar20]

Is that a headset spacer?

Yeah, 11/8 with the internal diameter opened up a little.

 

[folmonty]

Can anyone verify the Bosch part number for the chain ring lock nut? I've found these three PN# Think it's the first one but want to verify? Thx

Bosch 1270.014.085



Bosch 1270.016.428
Bosch 1270.016.489

 

[Zaskar20]

Can anyone verify the Bosch part number for the chain ring lock nut? I've found these three PN# Think it's the first one but want to verify? Thx

Bosch 1270.014.085



Bosch 1270.016.428
Bosch 1270.016.489

 

[Wodger63]

So a quick poll, who use's an alloy chainring/spider and who use's a steel chainring?
Is there a connection between alloy chainrings coming loose and steal not?
My Powerfly 4 came with a DM FSA steel chainring 36T with an O ring, I replaced it with a DM eThirteen steel chainring 38 T with no O ring as there was no recess for it.
(I noted on removal of the OEM FSA chainring the lock nut although not loose, it did not seem as tight as I expected. This was at 1500klms)
Little bit of grease on the threads, did it up goodintight with the right tool, over 1000klms of mixed riding no issue.
I did check it after the first 100klms or so by giving it a tap with a flat blade screw driver and hammer, it was tight and I haven't worried about it since.

 

[folmonty]

So a quick poll, who use's an alloy chainring/spider and who use's a steel chainring?
Is there a connection between alloy chainrings coming loose and steal not?
My Powerfly 4 came with a DM FSA steel chainring 36T with an O ring, I replaced it with a DM eThirteen steel chainring 38 T with no O ring as there was no recess for it.
(I noted on removal of the OEM FSA chainring the lock nut although not loose, it did not seem as tight as I expected. This was at 1500klms)
Little bit of grease on the threads, did it up goodintight with the right tool, over 1000klms of mixed riding no issue.
I did check it after the first 100klms or so by giving it a tap with a flat blade screw driver and hammer, it was tight and I haven't worried about it since.

eThirteen steel chain ring (stock). Mine has been good since new. Checked it last weekend after just shy of 1000 Km and it was tight. Never been off yet, so assume it's still got that o-ring as stock. Put register marks on both since new so as to ID any issues ASAP. In my riding there aren't any real G-outs with drops and jumps which are what I believe are the primary cause of it backing off.