e thirteen chainring on Bosch Gen 4 CX has come loose, not sure why

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edruid

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Just cleaning the chain and noticed rattle, which was coming from the crank. On investigation I found chainring was loose. The slotted bolt circle in red is just flapping about and there does not seem to be anything for it to thread onto. I'm not sure what I'm looking at? Has it snapped off a piece that goes inside? My crank puller won't work as there is nothing for it to push against. The chainring was changed by the shop a few months back - but boy am I sick of the schlepp to that shop so if I'm missing something and it's an easy fix please let me know. Thanks!

155 chainring.png
 
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This thread might help.

Bosch Gen 4 Chainring Nut printed Torque of 25 to 30 NM is likely wrong

After following Bosch instructions (grease don't loctite) the chain ring lockring nut to 25 to 30 NM and having it fall off 3 times I was pretty annoyed and about to start looking into drilling it out and using safety wire. I even went to the local Trek Dealer and had them torque it down in case...
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It’s my understanding that the torque has been increased for the castle-nut. It may be printed on the new castle nuts.

My chainring came loose also …but that was after I had reused and re-torqued the same nut 3 times. I won’t do that again. I replace the nut with new and keep a spare.

No loc-tight, no grease, no more problems.

Steady your bike while applying the final (reverse thread) torque. I now use 35-40nm. Constant pressure …no jerking motion.

If you’re unsure …refer to the specs. Follow the instructions for a new thirteen chainring.
 
edruid said:
Just cleaning the chain and noticed rattle, which was coming from the crank. On investigation I found chainring was loose. The slotted bolt circle in red is just flapping about and there does not seem to be anything for it to thread onto. I'm not sure what I'm looking at? Has it snapped off a piece that goes inside? My crank puller won't work as there is nothing for it to push against. The chainring was changed by the shop a few months back - but boy am I sick of the schlepp to that shop so if I'm missing something and it's an easy fix please let me know. Thanks!

View attachment 160812
Click to expand...
There is a washer for the crank retainer bolt to press against. That must be removed for the crank removal tool to work properly. Carefully thread the tool with your fingers until it bottoms out or becomes tight.

Within a few turns you should see the crank moving out. The torque on that bolt is 50nm, when reinstalling.

For detailed methods refer to YouTube. That’s what I did the first time.
 
irie said:
Good luck. Go slowly and thoughtfully and you'll be fine.
Click to expand...
Yesterday I R/R ‘d the Bosch motor on a friends Rail 9.7 2020. (I have a spare rebuilt motor) .
IMG_0115.jpeg

The bracket bolts sheared off on one bracket only. I carefully inspected the nearest motor mount bolt and discovered a very small fracture in the carbon which surrounds the motor mount insert. Barely noticeable but there was extremely slight movement. Bad news for my buddy. That frame needs to be replaced.

I got him up and running again, with the spare rebuilt motor, but I didn’t install a new castle nut or bearing seal kit. I added a little more torque to the important stuff (castle nut and motor mount bolts (6). “Ride carefully “ I said.

This may be a warranty (lifetime for the frame) issue but he’ll need to jump through the hoops with the local Trek dealer first. I’ll accompany him for the initial visit/inspection and flex my purchasing influence (sometimes that works 🤞).

We discussed the possible scenario’s that could happen for a frame replacement. Hoping for the best …expecting the worst.
 
Stihldog said:
Yesterday I R/R ‘d the Bosch motor on a friends Rail 9.7 2020. (I have a spare rebuilt motor) .
View attachment 160943
The bracket bolts sheared off on one bracket only. I carefully inspected the nearest motor mount bolt and discovered a very small fracture in the carbon which surrounds the motor mount insert. Barely noticeable but there was extremely slight movement. Bad news for my buddy. That frame needs to be replaced.

I got him up and running again, with the spare rebuilt motor, but I didn’t install a new castle nut or bearing seal kit. I added a little more torque to the important stuff (castle nut and motor mount bolts (6). “Ride carefully “ I said.

This may be a warranty (lifetime for the frame) issue but he’ll need to jump through the hoops with the local Trek dealer first. I’ll accompany him for the initial visit/inspection and flex my purchasing influence (sometimes that works 🤞).

We discussed the possible scenario’s that could happen for a frame replacement. Hoping for the best …expecting the worst.
Click to expand...
Ooh, that's not pretty.
 
Stihldog said:
Yesterday I R/R ‘d the Bosch motor on a friends Rail 9.7 2020. (I have a spare rebuilt motor) .
View attachment 160943
The bracket bolts sheared off on one bracket only. I carefully inspected the nearest motor mount bolt and discovered a very small fracture in the carbon which surrounds the motor mount insert. Barely noticeable but there was extremely slight movement. Bad news for my buddy. That frame needs to be replaced.

I got him up and running again, with the spare rebuilt motor, but I didn’t install a new castle nut or bearing seal kit. I added a little more torque to the important stuff (castle nut and motor mount bolts (6). “Ride carefully “ I said.

This may be a warranty (lifetime for the frame) issue but he’ll need to jump through the hoops with the local Trek dealer first. I’ll accompany him for the initial visit/inspection and flex my purchasing influence (sometimes that works 🤞).

We discussed the possible scenario’s that could happen for a frame replacement. Hoping for the best …expecting the worst.
Click to expand...
Oooh dear cracked carbon not good, I worry about mine! Good luck at the shop!
 
This is a well-known problem. There is an O-ring for under the nut and then it will bi ok.
 
Hiltix said:
This is a well-known problem. There is an O-ring for under the nut and then it will bi ok.
Click to expand...
Well the o ring was there before and it wasn’t ok. At least I have the tools to check and sort it myself now (except the 1/2 inch torque wrench🙄)
 
irie said:
Our Trek Rails came without the O-ring fitted to their Bosch CX Gen 4 motors.

An O-ring is not a locking device.
Click to expand...
Yeah, my Rail didn’t have the thin rubber “O” ring either …but this motor did. The shape and thinness indicated that it belonged between the chainring and castle nut. It never “squished” out when I applied the torque to the castle nut. (That was my worry). The Rubber O ring was very thin and somewhat shaped like the motor axle. (My bad description If you know what I mean)??
 
edruid said:
My o ring was metallic (2024 cube 155 MT)
Click to expand...
When I installed a new ethirteen chainring I didn’t use any type of “O” ring between the castle nut and chainring.

However, there were two “O” rings between the chaining and motor (one was brass and the other was thin plastic. I reused the plastic O ring and had to remove the brass one. Because of the shape of the new ethirteen chainring …I didn’t need the brass ring …which pushed the new chaining out of alignment. (If that makes sense?)
 
A new O-ring (Bosch Art # f. CX4: 1270016119) should be used each time the lockring is removed.
It's imho not a good Solution, kind of Workaround, but it works 🤷‍♂️
 
Hiltix said:
To solve the Problem TO ist asking for. Loos Lockring.
Click to expand...
The O-ring does not permanently solve the loose castle nut problem - solutions are discussed in the below thread:

www.emtbforums.com

Bosch Gen 4 Lock Ring

I have recently replaced the chainring on my Trek Rail and noted that there was no rubber O ring fitted between the lock ring nut and the chain ring. I believe there is supposed to be one. The chain ring was a SRAM type, which I have replaced with a KMC. I just refitted the nut and torqued it...
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My pivot shuttle came with an o ring between the chainring and the motor shaft bearing. No o ring between the castle nut and the chainring.

My LBS showed me a new stock castle nut that was black, aluminum and was stamped with 35 Nm. They were not thrilled when I said that the shop in Sedona lock tighted my nut when it came off on trail. They recommended a new nut with just grease the next time it came loose. (if):)

—Jason
 
irie said:
The O-ring does not permanently solve the loose castle nut problem - solutions are discussed in the below thread:

www.emtbforums.com

Bosch Gen 4 Lock Ring

I have recently replaced the chainring on my Trek Rail and noted that there was no rubber O ring fitted between the lock ring nut and the chain ring. I believe there is supposed to be one. The chain ring was a SRAM type, which I have replaced with a KMC. I just refitted the nut and torqued it...
www.emtbforums.com www.emtbforums.com
Click to expand...
In my case it did - Since over 2Y with lots of rough stuff and Races (y)
 
The e-thirteen chainring doesn't have a recess for the nitrile o-ring, they recommend not using the o-ring. The Bosch design says use an o-ring.
I used a ring that had the recess for the o-ring to spread but not displace, it was one piece with no shim/spacer, and also tightened up 'f' tight and used a little loctite 👍
 
DaveG01 said:
The e-thirteen chainring doesn't have a recess for the nitrile o-ring, they recommend not using the o-ring. The Bosch design says use an o-ring.
I used a ring that had the recess for the o-ring to spread but not displace, it was one piece with no shim/spacer, and also tightened up 'f' tight and used a little loctite 👍
Click to expand...
By the time you've done that the O-ring (probably nitrile) will be so compressed that it be doing absolutely nothing, pointless fitting it.
 
edruid said:
Just cleaning the chain and noticed rattle, which was coming from the crank. On investigation I found chainring was loose. The slotted bolt circle in red is just flapping about and there does not seem to be anything for it to thread onto. I'm not sure what I'm looking at? Has it snapped off a piece that goes inside? My crank puller won't work as there is nothing for it to push against. The chainring was changed by the shop a few months back - but boy am I sick of the schlepp to that shop so if I'm missing something and it's an easy fix please let me know. Thanks!

View attachment 160812
Click to expand...
This seems to be a common issue on these although, thankfully, I've not had it myself. Many people have said it's just caused by poor building of the bike in the shop. Drop of thread lock and torqued correctly should sort it but take it back to the shop if they've not done it correctly.
 
Steve Gibson said:
This seems to be a common issue on these although, thankfully, I've not had it myself. Many people have said it's just caused by poor building of the bike in the shop. Drop of thread lock and torqued correctly should sort it but take it back to the shop if they've not done it correctly.
Click to expand...
One hour round trip to LBS plus loading unloading x4 plus queue plus humming plus ahhhing plus doing … I just up and bought the lock ring tool for 25 quid and done it myself. Only thing is I now have ANOTHER item on my checklist :(
 
Mine came loose. No oring fitted as standard. Cube 2023 reaction race hybrid. My only tip would be cleaning it up properly so that all the mating services are free of debris grit etc. E. G. your chainring is seating metal to metal then the specified torque should work. I'm using 30 NM, no threadlock, no grease on thread and just check chainring for play regularly.
 
Just for clarity the diagram shows the o ring. As @irie pointed out it serves no purpose in terms of torque.....a butile o ring is merely a seal.
With the repeated reports here of chainwheels coming loose most focus is on getting the lockring tightened. To repeat what I have previously advised, always use a new lockring and o ring. The lockring is thin with few threads and is ally. It is fitted to a splined steel shaft. When torqued correctly the thread will be spread slightly to achieve maximum friction. If it comes loose.....it is scrap! It is best fitted clean and dry...no grease.
Then often ignored, is the issue of why it came loose in the first place. The lockring has a reverse thread. The shaft rotates clockwise. Therefore just like pedal fitment it should not have forces trying to unthread it. The only thing that could apply a clockwise rotational force is the chainwheel. If the chainwheel allows any movement under rider pressure on the driveside crank it will deliver that force. So if fit on the splined shaft is not perfect, or if there is flex beyond the centre spline section, the chainwheel can loosen the lockring. My preference is always a steel chainwheel.
 
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