Bosch CX gen 4 chainring nut

[Philly G]

@dixie600mhz Glad you were able to get it sorted. I know what you mean though, I'm the same with cassette lock rings, light alloy components and easy to cross thread. And yes the chainring is super close to the chainstay. I'm dreading when the time comes to replace my chainring, I used red loctite on the lock ring nut which apparently was a mistake, it might not come off in one piece ! ? but at least its never come loose ?

 

[folmonty]

@dixie600mhz Glad you were able to get it sorted. I know what you mean though, I'm the same with cassette lock rings, light alloy components and easy to cross thread. And yes the chainring is super close to the chainstay. I'm dreading when the time comes to replace my chainring, I used red loctite on the lock ring nut which apparently was a mistake, it might not come off in one piece ! ? but at least its never come loose ?

You'll probably have to use heat to remove it. How much is the question?

 

[Philly G]

You'll probably have to use heat to remove it. How much is the question?

I'm kinda hoping I'll get away with it, I used red loctite on the motor mounting bolts too and I've had the motor out several times without issue. I have now banned myself from using red loctite anywhere on my bike?

 

[Mikerb]

I'm kinda hoping I'll get away with it, I used red loctite on the motor mounting bolts too and I've had the motor out several times without issue. I have now banned myself from using red loctite anywhere on my bike?

stop worrying!! If the bolts/nut are ally the loctite will not have bonded unless you used a primer first. It is probably just acting to add resistance to the threads loosening rather than "locking".

 

[folmonty]

@Dr. Ergal - best solution I've seen and great excuse to get couple of new tools? FWIW the UNIOR 1671.2/4 is available in the US from the mfg for $24.67 shipped. I'd consider this tool a must have for any Bosch Gen 4 CX equiped bike.

 

[skeet103]

@Dr. Ergal - best solution I've seen and great excuse to get couple of new tools? FWIW the UNIOR 1671.2/4 is available in the US from the mfg for $24.67 shipped. I'd consider this tool a must have for any Bosch Gen 4 CX equiped bike.

So I have the same problem and I've only ridden about 100 miles...luckily it happened on an access rode as I was riding up to do another loop

So I understand I will need the lock ring tool, but as I have not really done any maintenance on my trek yet, I assume I need a crank puller as well? Or do the cranks arms just pop off?

 

[WilkyWay]

@skeet103 you’ll need an arm puller as well.

 

[Shy Ted]

If it’s any help at this point I can say that way-back-when in this thread I had the loose nut issue I cleaned the threads, applied blue locktite, discarded the o-ring and tightened up the ring with the help of a blunt object (screwdriver wrapped in cloth) and a wooden mallet; it’s now stayed on for about 800 off road miles, over all sorts of terrain, wet, boggy rocky......etc.

 

[Timmoh]

If it’s any help at this point I can say that way-back-when in this thread I had the loose nut issue I cleaned the threads, applied blue locktite, discarded the o-ring and tightened up the ring with the help of a blunt object (screwdriver wrapped in cloth) and a wooden mallet; it’s now stayed on for about 800 off road miles, over all sorts of terrain, wet, boggy rocky......etc.

Did the same 1000 mile age and still on. I also used a blob of paint/enamel to mark the nut and ring so that I can check any loosening at a glance (all car engines have this done for warranty purposes).
Simple and quick.

 

[HORSPWR]

all car engines have this done for warranty purposes

Car engines have this done in the factory so that during the inspection checks it can be determined if a bolt has been forgotten to be torqued, not to see if they come loose later on after the car goes into service.

 

[PetrD]

Was same problem, Trek Rail 7, bosch perf cx4. I cleaned everything and for lock I used wife's nail polish. After 300km everything keeps well.

 

[selenium]

Yes, I had the same problem when my bike was new.

I noticed the lock ring was loose after the chain fell off on the 3rd ride. The chainring was flopping around as the pedals were turned.

It could be tightened by hand, but would repeatedly come loose every couple of miles.
Tightening with a hammer and screwdriver will work for a few miles, but will dent the aluminum lock ring and is not permanent.

After pulling the crank and using the special Bosch lock ring tool to tighten it to 30 Nm, it has not come loose over an additional 500 mi. of technical singletrack.

As others have noted, not everyone has easy access to a bike shop. This is easy to fix on your own, but you will need:
* Crank Puller
* Bottom Bracket Tool
* Torque Wrench (optional)

The Gen4 setup requires an 8-pin tool, such as the Park Tool BBT-18, which is the one I used, but that one doesn't have a square ratchet hole, so can't be easily attached to a torque wrench. So the Unior tool would be better in that regard. I purchased a 12-sided socket from Lowe's, in order to adapt the BB-18 to my torque wrench.

The torque wrench could be optional for mechanics who know what that 30N-m feels like, but:
* 30 N-m is not very much and could easily be over-tightened without a torque wrench
* I used 30 N-m (or just a hair more), it has not come loose, in all temps and mostly-dusty technical terrain (quite a few rocks and small 1m drops).

 

[Zed]

Can anyone confirm/deny if Shimano TL-UN96 also fits? Hard to tell searching. I might have to pop off the crank arm and try it.

 

[MsO]

Undo the locking ring put some lock thread around the thread tighten up with hammer and blunt screwdriver hasn't come loose in over 1000 miles?

 

[Philly G]

Can anyone confirm/deny if Shimano TL-UN96 also fits? Hard to tell searching. I might have to pop off the crank arm and try it.

I'm 99% certain that Shimano tool is the one. I got this one for an after-market screw-fit BB to replace the hideous $20 press fit BB my Trek Remedy had. It also fits the Bosch lockring and looks the same as the Shimano tool

11D3 BB Lockring Tool (IceToolz) | Shockcraft

Heavy duty tool for installing and removing all eight-notch bottom bracket cups, including Monocrome SF41 & SF46, Shimano, ISIS Drive, ISIS Overdrive Also fits Shimano crankset lockrings Fits a 32 mm hex socket so a torque wrench can be used

www.shockcraft.co.nz

 

[Dr. Ergal]

Hi guys, sorry for my absence

I come with some (sad) update
Probably due to the very severe use (I'm coming, without any false modesty, pretty faster in enduro trails), the nut has come totally loosen despite of the safety wire lock.
The fault is totally mine because I did not check it for many rides, so that the nut has come totally loosen until the threads got totally DESTROYED. Movements and vibrationshave been huge, surely.

That's the result: the thread totally gone

Then, I probably need something more efficient
I decided to make an experiment, and I want to share it with you.
I decided to "package" the nut (I bought a brand new spare, of course) with the crank itself by using some shims, so that the crank will keep the nut in position and will ensure it to not come undone.
Obviously, the crank cannot compress directly the nut, 'cause otherwise it couldn't rotate backward (chainring and crank must be independent) so I put a thrust bearing in between. In this way I physically pack the nut by the crank, but at the same time I can keep the crank and the chainring independent and disconnected.

Obviously (2) I did NOT pack the nut by compressing it with the crank: the shim pack is designed to have a thickness very slightly less than the room between nut and crank; in this way I just pack it without any compression force

IT WORKS !!

I tested in 3 very hard rides, so far, and the chainring keeps stable and smooth. Moreover, the crank action sound much smoother (probably because of the tight connection, that prevents any creaking or crunch)
In this way, the only thing I must check is the crank bolt tightening, because that's what packs all the system.

I perfectly understand that it could sound bizzarre and unusual.
I still have some concerns too, to be totally honest.
Nevertheless, it really seems to work very well, with a very tight and smooth action.
If it works, I think I found the final solution

I'll keep you updated about the result of a long run test

 

[Philly G]

@Dr. Ergal sorry to hear about the demise of your original lock ring nut, but you have devised a rather clever solution. I will be interested to see how it all works out going forward. Luckily it was just the nut that got damaged

 

[Dr. Ergal]

I will be interested to see how it all works out going forward. Luckily it was just the nut that got damaged

Theoretically, the nut is isolated by the compressione solicitation and the wearing as well, because there are some shims: the shim incontact with the nut rotates with the nut itslef, while the shim in contact wit hthe crank rotates wit hthe crank itself. In between, the thrust bearing isolated the two parts by their own rotation direction
Then, the nut is tighened by its own thread against the chainring (as designed), and also is just "touched" by the shimpack that prevent it to shift outward

Anyhow... the theory looks smooth but... you know... only the time will give us a proper and ultimate feedback
I'll keep you updated

 

[Mikerb]

It sounds like a fix but surely the solution is to find out why the nut comes loose in the first place given that several brands use the same nut to secure the chainring and they do not seem to suffer the same outcomes. The specified torque is what ensures fixings remain secure helped if necessary ( e.g. a fixing subject to vibration) with a threadlock.
This fixing comprises a short threaded section that is "open" so provided the thread is clean the nut should go on with no grease and torqued to spec. Putting grease on the thread would definitely compromise the fixing by reducing the friction created by the specified torque between the thread surfaces. A little blue locktite would be advisable...and left to set for 24 hours. A locknut that has come loose should not be re used since the thread tolerances will have been damaged.

 

[Planemo]

surely the solution is to find out why the nut comes loose in the first place given that several brands use the same nut to secure the chainring and they do not seem to suffer the same outcomes.

I've have tried to keep my ear to the ground with this lockring issue as I have a Gen4 in my Haibike but its still very firmly attached after 500 miles since new. Is there a consensus on what manufacturers do seem to give issues?

 

[Mikerb]

I've have tried to keep my ear to the ground with this lockring issue as I have a Gen4 in my Haibike but its still very firmly attached after 500 miles since new. Is there a consensus on what manufacturers do seem to give issues?

I have a Whyte E180RS which is a DM chainring on the Bosch gen4 and have had no problems with that either.

 

[Planemo]

I have a Whyte E180RS which is a DM chainring on the Bosch gen4 and have had no problems with that either.

Interesting. Mine is a 38t SRAM, so thats 2 different manufacturers that appear to be OK. Do we think this problem is likely down to the make of the chainring, or simply the initial builder not using enough torque on the lockring? Given all the motors are essentially the same and theres not much else that could contribute to the lockring coming loose, I can't see what other factors could instigate it.

 

[Mikerb]

Interesting. Mine is a 38t SRAM, so thats 2 different manufacturers that appear to be OK. Do we think this problem is likely down to the make of the chainring, or simply the initial builder not using enough torque on the lockring? Given all the motors are essentially the same and theres not much else that could contribute to the lockring coming loose, I can't see what other factors could instigate it.

...by DM I was stating it is a direct mount chain ring. Mine is also SRAM ...34t.

 

[MrPeaski]

I've been keeping an eye on this thread, and until today mine has been fine.
However, cleaning and lubing the chain today I found the chain ring loose and after pulling off the crank arm the locknut had come undone. Fortunately there is no damage to it as it was only a couple of turns, but must have been like it for a while and I've not noticed.
Mine is a 2020 Cube stereo 160 AT, with a 36T Alloy E-Thirteen direct mount chain ring.

I've seen an O ring mentioned but there wasn't one on mine.
My biggest headache was that I'm going out on it tomorrow and didn't have the proper tool to tighten it up.
A drift is difficult to get in as the lockring sits a lot further in to the ring than those pictured earlier in this thread.
I've ended up modifying an old school pin tool and blue threadlock to do the job until I can get the proper tool and do it properly.

 

[Mikerb]

Maybe the issue here is that ally is just not strong enough to resist the forces imposed by rider plus motor most especially when the chainline is at the extremes of the cassette. If the chainring is deforming it could well be transferring a sideways force on the threads of the locknut effectively misshaping them. In which case the locknut is not coming loose due to vibration or kick back from the rear triangle but rather by a twisting action on the threads. So maybe a steel chain ring would resolve these issues??

 

[Planemo]

...by DM I was stating it is a direct mount chain ring. Mine is also SRAM ...34t.

Apologies, divvy moment there! I didn't put 2 and 2 together because I couldn't see how being a DM would make any difference.

 

[Planemo]

Maybe the issue here is that ally is just not strong enough to resist the forces imposed by rider plus motor

Good point. Is it primarily alloy DM chainrings/spiders that are causing the problem?

 

[Mikerb]

Good point. Is it primarily alloy DM chainrings/spiders that are causing the problem?

It is too small a sample on the forum to draw absolute conclusions but a spider mounted chain ring has more support than one that is direct mounted. The Trek and I think also the Cube Stereo reported here with the problem were both e 13 chainrings...that may be coincidence but its design does seem to optimise low weight rather than strength.

 

[Dr. Ergal]

It sounds like a fix but surely the solution is to find out why the nut comes loose

You're definitely right!
In fact, I'm going to keep the issue observed to detect the primary fact which determines this problem.
As many of you reported, not all Bosch Gen4 suffer this issue; it means that something specific (and not related to the desig itself) does.
It could be the severe enduro/dh usage, which determine a huge kick back effect
It could also be a not perfect tightening (dirt on thread, low torque, lack of threadlocker, etc etc).

I can't work on the first hypotesis because I only do enduro (and I'm not going to use the bike in quiter way... ); then, I just work on the second case.
I applied the proper torque by using torque wrench and the proper tool to engage the nut; also, I accurately cleaned the thread and applied medium threadlocker. Then, the specs of the "experiment" are clear, now.
If the nut will come undone again, I'll aplly strong threadlocker in place of medium.
I also would really like to install a direct mount chainring, but it seems that, unfortunately, the smallest available is 34t, while I use 30 or 32 max

In conclusion, thanks a lot for your all your thoughts: they are a valid analysis basis (I don't find anything similar in other forums; a point for you )

 

[MrPeaski]

As an alternative to the Unior 1671.2/4 tool, this one by Lifeline also works.

BB Tool 8 Prong

Buy your LifeLine BB Tool 8 Prong - Bottom Bracket Tools from Wiggle. SAVE 16% - RRP £11.99 now only £9.99. Free worldwide delivery available.

www.wiggle.co.uk

Delivered this morning, and confirm it fits and I've tightened my lock ring up properly.