Bosch CX gen 4 chainring nut

[WilkyWay]

Chainring nut / spider nut or other names...
Has anyone experienced their chainring nut coming loose?
Today is the first day my Rail has let me down, I had to cut my ride short today when I felt a vibration at my feet, checked the chainring and it was wobbling and the spider nut had come completely undone... anyone experienced this?
I made myself a tool to tighten it back on today and will check it again next time out. Has anyone else had this happen on a Gen 4 motor or van I put it down to a build issue?

 

[Blue Moon]

Chainring nut / spider nut or other names...
Has anyone experienced their chainring nut coming loose?
Today is the first day my Rail has let me down, I had to cut my ride short today when I felt a vibration at my feet, checked the chainring and it was wobbling and the spider nut had come completely undone... anyone experienced this?
I made myself a tool to tighten it back on today and will check it again next time out. Has anyone else had this happen on a Gen 4 motor or van I put it down to a build issue? View attachment 27677

I found this nut loose on my wife’s Rail 7 (same as above) yesterday. Off to LBS this morning to have it tightened up. This seems quite common, is there a re-call from Bosch regarding this?

 

[WilkyWay]

I haven’t been contacted but it’s becoming more and more common. I’d advise everyone with a gen 4 motor to check the nut and mark it so you can see if it is becoming loose.

 

[Aleksiron]

Yes i experienced it too. 30ish newtons are not much for that. i dont understand why there is left handed threading because it tries loosen itself when pedaling.. LBS also told that you dont want to over tighten that nut because it may break speed sensors inside the motor

 

[Aleksiron]

Is it a Bosch issue, or a Trek issue?

The nut has remained solid on my Whyte after 800 miles.
But I could do with sourcing a reasonably priced tool and knowing the torque setting, as the bike is eating chains and a cassette, so the chain-ring won't be far behind.

Bosch issue. I have Cube Stereo Hybrid.

 

[Aleksiron]

Interesting, thanks.

Another thread says the Unior 1671.2/4 tool fits, at £19 not too painful.
Just have to source a replacement chain ring now.

Yep i recommend to get a spider tool and crank puller so you can check it once in a while.

chainrings, if you do commuting or something else than going trails too, i recommend 36t chainring. i dont know about whytes original chainring size but my cube had 34t. I have spare 38t too. 36t feels good on roads but still dont lose uphill capabilities in trails. I have 11-50 rear. I have badassbox so original chainring out pedaled too fast.

Bit offtopic but just for you information!

 

[zaykay]

Mine was also loose (Rail 7). Added Loctite when tightening.

 

[Jay355]

Chainring nut / spider nut or other names...
Has anyone experienced their chainring nut coming loose?
Today is the first day my Rail has let me down, I had to cut my ride short today when I felt a vibration at my feet, checked the chainring and it was wobbling and the spider nut had come completely undone... anyone experienced this?
I made myself a tool to tighten it back on today and will check it again next time out. Has anyone else had this happen on a Gen 4 motor or van I put it down to a build issue? View attachment 27677

Hi, had exactly the same issue with a Haibike at 250miles on the clock. I thought it was just due to being new but clearly something I shall monitor closely.

 

[Like a Boss]

Bosch specifies an o-ring between the chainring and chainring nut....bosch part number 1270016119. It seems to be for one-time use. I removed and replaced the chainring and now the o-ring wants to bunch up and squirm out of place. There is no groove for the o-ring. But the technical support line from Bosch says it must be there. I'm not impressed with this design, nor the fact that the nut tightens in an opposite direction of pedaling, nor the fact that the chainring nut is aluminum and seems delicate (there will be aluminum shavings as you remove and replace the chainring nut). I have heard that some shops in the USA are using loctite, and one mechanic admitted that they were not using the o-ring. Trek does not have the o-rings, and other than some European online sites, I can't find the o-rings in the USA.

 

[qwertycube]

Not fully investigated yet, but 2 day old CUBE Reaction EXC and front ring is clearly loose. Gears weren’t setup when I got the bike and I struggled to get them to index - any tips? But 2nd ride out today and gears got progressively worse and finally unusable, so headed home. But also noted the front chainring is loose and wonky!
Very disappointed in the bike. Made all the worse that my wife’s Trek PF5 arrived first and I had been out on that. What a fabulous smooth and quiet bike. The CUBE is a crude noisy bag of nails by comparison!

 

[MsO]

I've got a trek rail 7 fitted with speed box over 650 miles no issues with chain ring heard about this before coming loose gave it a tap with screwdriver and hammer not came loose yet ?

 

[raymondo]

Mine cane undone a few times, no big deal. Tightened by hand and used a tyre lever to help for the last bit. This was on the trail, tightened up properly at home.

 

[vikilibra]

Signed up to this forum specifically to resolve this issue. My spider nut came undone and I had not noticed it until the chain started dropping off at the front on the highest three gears! With the COVID crisis not all shops are open so decided to tighten it with two screwdrivers. Tightened until the pedal started turning backwards and it is working without any issues. Will keep an eye but a big Thanks to this thread for the info. Otherwise I would have not worked out that the screw tightens against the pedalling direction.

 

[GrahamPaul]

Interesting, thanks.

Another thread says the Unior 1671.2/4 tool fits, at £19 not too painful.
Just have to source a replacement chain ring now.

Where did you source the chain ring, please?

 

[GrahamPaul]

I haven't been able to source a new chain ring in the UK yet.
New chain and cassette fitted, and managing on the original chain ring for now.

I was told the distributor UK ZiroFisher was getting stock early June, for order by local bike shops.
They may take a while to emerge on UK on-line retail.

Ah, okay. I'm looking for the Shimano version.

I see that the SRAM chainrings are available in Germany for a lot less than the Ohio dealer wants. (Sorry, comes up in Spanish. It will probably appear in English if you do a refresh).

SRAM Plato X-Sync 2 Eagle Direct Mount Boost para Bosch Gen4

El plato SRAM X-Sync 2 Eagle Direct Mount para ruedas Boost con motor Bosch de la 4ª generación El plato SRAM Eagle para líneas de cadena Boost se acopla mediante Direct Mount y fue desarrollado para E-Mountainbikes con motor Bosch de la 4ª generació

www.bike-components.de

I'll keep looking for the Shimano ring. (Could it be the SLX M7100 12sp chain ring as per non-E?)

 

[GrahamPaul]

I haven't been able to source a new chain ring in the UK yet.

I should perhaps point out that the chain ring on my Focus Jam² is a FSA Megatooth G4 direct mount 34T with, what seems to be, an 8mm offset. This doesn't appear anywhere in the FSA catalogue. FSA do appear to be planning a direct mount spider to take replacement chainrings but, as yet, these are not available.

I have located a similar spider on the Miranda site which is double the FSA price (I guess I can live with that because it's only bought once) but there is no information about the offset, nor what material it's made from.

I've done over 2200km on this chain ring now and it's starting to show it. I can't imagine it will be long before the chain starts a merry dance on gear change. I want to avoid having the dealer do it with Focus parts because I looked at the price of the FSA direct mount chain rings which seem to be ten times the price of everyone elses.

 

[Dr. Ergal]

Badly, I join the chorus...

The lockring of my brand new Mondraker Level (35km only) got loose just after the first ride
Pulled out the crank and re-tightened, applying a lot of medium loctite

I'm sadly sure it won't be the last time...

 

[Dr. Ergal]

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

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

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

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

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.

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

 

[MsO]

Wow that was an interesting read and your solution will definitely work well done

 

[Like a Boss]

That's rad. I like it a lot. No reason for a chainring to come loose on a trail, and this solution will ensure that it doesn't happen. Thank you for posting.

 

[Dr. Ergal]

Glad you enjoyed

I really hope to get soon the chance to test it.

 

[Dr. Ergal]

FEEDBACK:
I'm aware it's too early, but I made 10 hard trails (Enduro and Downhill) without any issue
In one of these trail I got my first KOM (on descent), so I pushed a lot.
It seems that the mod works fine

Ah, one note more: even in the roughest descent I did NEVER heard kick-back rattling coming from the motor. It's quiet and smooth

 

[sandyman44]

FEEDBACK:
I'm aware it's too early, but I made 10 hard trails (Enduro and Downhill) without any issue
In one of these trail I got my first KOM (on descent), so I pushed a lot.
It seems that the mod works fine

Ah, one note more: even in the roughest descent I did NEVER heard kick-back rattling coming from the motor. It's quiet and smooth

hi
looking with interest at your pictures, what spider and chainring do you have please? was it with your bike as stock or did you change it?

I have a scott E-ride with bosch gen4. comes as stock with 34T sram x-sync2 direct mount, Boost chainline. I want to fit a smaller chainring, ideally 30T . This is because I often ride up very steep hills with unmotorised people with lower gearing, and I want to be able to ride with them when they are in their granny gear (22 ring 36cog on 27.5"), not zoom to the top and have a nap waiting. even when I am in 50T cog, the 34T ring makes my cadence unbearably slow to stay with them. I don't care about losing higher end pedal speed, with this bike I have no need to pedal more than 22 mph or so - I have never yet used the 11T cassette cog. so I want to change the chainring.

there is nothing available for any bosch direct mount less than 34T , but I was looking at using
this

Accessories and spare for bikes, ebike, motorcycles, scooter, vespa,

accessories and spare parts for cycle, ebike, motorcycle, scooter, vespa, sport

www.ridewill.it

or this

Spider 1x Bosch GEN4 engine bcd 104mm offset 53mm for boost frames FS

- Forged in AL6061 - 104mm - 53mm offset - Weight 66.5gr E-bike Drivetrain, Spider E-bike, Price 28.4EUR FSA Code 421589628 4710243882573

www.ridewill.it

although not ideal to have to buy from italy (I'm in UK)
and then any good 104BCD NW chainring, probably this in 30T 104BCD

Race Face Narrow Wide MTB Single Chainring | Chain Reaction

Race Face Narrow Wide MTB Single Chainring - Lowest Prices and FREE shipping available from The World's largest online bike store - Chain Reaction Cycles

www.chainreactioncycles.com

very open to hearing about any other parts options anyone has already looked at...

thanks

 

[Dr. Ergal]

looking with interest at your pictures, what spider and chainring do you have please? was it with your bike as stock or did you change it?
I have a scott E-ride with bosch gen4. comes as stock with 34T sram x-sync2 direct mount, Boost chainline. I want to fit a smaller chainring, ideally 30T

Hi

I'm totally with you: a 34T chainrgin is too big to decently use the bike and its battery. You are obliged to require too much assistance, and even the cadence is not good
To me, 30T is perfect. I installed a 32T only because the 30T leads the upper beam of the chain too close to the chainstay, but I had a 30T on my previous ebike and I can ensure that it's the right choice
Furthermore, I also had a Raceface narrow chainring, and I confirm that it's an excellent product.

The spiders you choosed are ok.
Just keep in mind that the 104-30T chairing is different than the others because it has NOT simples holes for bolts, but it's internally threaded, so the female bolt must be eliminated in the assembly.
Example:
Chainring 32T or more (through holes for bolts)

30T chainring (threaded holes for male bolts)


Because of what above, in case of 30T chainring you will need to install with the threaded protrusions facing INSIDE (beacuse of the machined part of the spider) and the bolts inside as well

It works; it's just pretty unusual

 

[sandyman44]

Hi

I'm totally with you: a 34T chainrgin is too big to decently use the bike and its battery. You are obliged to require too much assistance, and even the cadence is not good
To me, 30T is perfect. I installed a 32T only because the 30T leads the upper beam of the chain too close to the chainstay, but I had a 30T on my previous ebike and I can ensure that it's the right choice
Furthermore, I also had a Raceface narrow chainring, and I confirm that it's an excellent product.

The spiders you choosed are ok.
Just keep in mind that the 104-30T chairing is different than the others because it has NOT simples holes for bolts, but it's internally threaded, so the female bolt must be eliminated in the assembly.

30T chainring (threaded holes for male bolts)

Because of what above, in case of 30T chainring you will need to install with the threaded protrusions facing INSIDE (beacuse of the machined part of the spider) and the bolts inside as well

thanks. we're on exactly the same thoughts - I need to use emtb or turbo for my knees to cope with a 50-60 cadence up a hill. I'd rather be in eco or tour at 70-80 cadence to ride with non-motor family. If I am by myself doing a "downhill bombing session" then I emtb or turbo it up the hills at 80 cadence, but thats a different riding scenario.

Not sure if chainstay will come close or not yet, need some careful measuring. I've emailed raceface to ask for fitting instructions for their 30T.hopefully they will send me installation pictures.
am I right for your description that you would fit the 30T with the face of the ring that is normally "outside" facing inside? then the bolts come from the inside face of the spider, through the spider hole, into the chainring threaded hole? and then of course there's no nut, so the end of the bolt is visible on the outside. So the bolt length would have to be exactly right, enough to bite on all of the chainring hole's thread, but not so much that it sticks out and scrapes your shoes / ankles?
if not I can use the 32T like you, at least its a 2T gain.

 

[Dr. Ergal]

Yes, you understood perfectly.
It's not beautiful to see, but can work, by the mechanical point of view.
I wouldn't care about the extra-lenghtof the bolts; they will never interfer with your legs because they will anyway stay between your legs and the cranks. If you don't touch the cranks, you won't touch the bolts either

BTW, it's not a good scene to see...

 

[EMTBSEAN]

Hats off to you Dr Ergal for taking the time to type out your thoughts on this issue and take pictures of the steps to resolve it too, that’s what I love about this Emtb community forum, I’ll have to check mine as I’ve done nearly 1100 miles since I bought my Whyte E-150rs in March, I’ve got to admit I’ve not noticed any loose feeling but it’s a good to know about these things, thanks again Dr Ergal ?

 

[EMTBSEAN]

I might be totally wrong but if there’s a aesthetic issue would it be possible to tap a thread in the nut and insert a hardened grub screw that could be tightened up to the face of the spider, or even a location hole in the face of the spider for the grub screw to fit into, or am I over complicating things ?

 

[Dr. Ergal]

would it be possible to tap a thread in the nut and insert a hardened grub screw that could be tightened up to the face of the spider, or even a location hole in the face of the spider for the grub screw to fit into, or am I over complicating things ?

That's not a bad idea
You may use allen bolts caps like the following

Aesthetic may be not a technical issue, but it's an issue at all (for "fancies" like me, at least ? )

 

[EMTBSEAN]

Thanks for that idea mate, the caps look good, I like things to look right as well, I was never a big fan of Barry Bucknell ?