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

[Flupke]

Okay so Europe and US Bosch disagree.

Indeed. Or verbal statements differ from written statements as the latter could engage responsibility in case a strong torque would create damages.

you could try to get a written statement of the US support, as I managed to get in EU

 

[Peaky Rider]

Loctite it is then.

 

[vman]

Indeed. Or verbal statements differ from written statements as the latter could engage responsibility in case a strong torque would create damages.

you could try to get a written statement of the US support, as I managed to get in EU

I have tried several times to obtain a written statement but so far Bosch is not willing to put the new spec in writing, instead they are going around to local bike shop/bosch dealers and verbally telling them the new spec and having them update all the bikes on the floor to the new spec. This is not an ideal situation for consumers. I have tried my best to provide all the facts I know to this user community as I don't want anyone to get their ride or vacation ruined over a dropped off chain ring as we almost did.

 

[Mikerb]

I did a quick online search both of suppliers and various "ebike" companies who tend to provide more guidance alongside products. There was a bsolutely no sign of any change to the original torque settings. As far as I know Bosch do not manufacture fasteners but outsource that to the relevant suppliers. Those suppliers use engineering tables to determine a torque setting for fasteners they manufacture ( material, thread length, thread pitch etc). It seems ludicrous to me that anyone could propose increasing torque for a fastern assessed in that way from 25/30 nm to up 45nm....a 50% increase!!

 

[vman]

FWIW - TQ 50 NM, Brose 50 NM and Shimano 35 to 45 nm is the lockring torque spec for essentially the same part on a very comparable ebike motor ie. use scenario- so it is likely the Bosch outsource manufacture just got it wrong when they thought 25 to 30 nm would work given the amount of lockring issues that have been reported for Bosch bikes vs. almost none I have heard of for Shimano or Brose.

Unfortunately bike manufactures (unlike airplanes and cars) don't seem to take this stuff seriously enough to recall/throwaway parts so they have a habit of just keeping the old stuff in inventory even though it may have a improper label. TQ is doing this as well apparently - from Fuel EX thread " Torque should be 50Nm. Some older lockrings were stamped with 30Nm, but they can come loose. Mine did, 50Nm solved it."

Good luck with however you decide to resolve the aforementioned, I sleep well at 40 nm and have since never lost a lockring on either bike.


V

 

[Mikerb]

As far as I can see Brose etc specify the same 25-30nm.

Interesting that the torque for the lockring that attaches the chainring to the crank on a standard ( non E) bike is 40nm. I wonder if that is where the confusion is.

 

[vman]

See attached

 

[vman]

Confirmed with local Specilized dealer it is 50 NM just like Shimano is 35 to 45 nm.

 

[TommyC]

How do I stop notifications? This is getting really boring now!

 

[vman]

Good idea just hit unwatch on the thread, I just did so I am out going forward. Good luck guys.

 

[oscarbravo]

I have always used 30nm and never had any problems. I find it unbelieveable that an ally nut with so few threads would need or even survive 50nm!! I also wonder how many have a torque wrench for anti clockwise threads!

I believe the issue of chainrings coming loose for folk starts with the original installation being poor, and is followed by people then re using the lock nut after it has come loose...only for it to come loose a gain even if correctly installed this time. The reason I would suggest is that the minimal amount of thread on the locknut has been damaged. It is also the case that the initial installation may have involved too much torque (power tool used??).

With a bolt/machine screw, exceeding the engineering book torque risks shearing the bolt at its weakest point......where the thread initiates a fter the head of the bolt.

With a nut, it is different. The correct torque will apply the maximum friction between the threads of the nut and the threads of what it is fixed to. The correct torque is only marginally below the shear point and will involve some "spreading of the thread shoulders. So re using that nut may or may not be possible depending on how much spread occured in the threads.

Either way for the sake of c £10 the safest course of action is to always use a fresh lock nut.

Yes, blue loctite will also work but it depends how damaged the nut is......and it will make it more difficult to remove if needed.

I have four torque wrenches they all work clock or anti clock

 

[Mihael]

Hi!

So, to keep it short; count me. Unfortunately. After 600+ km; Bosch Performance Line CX Gen 4 on Cube; I was just pedaling to store; 2km from home; it got completely loose, so got lucky there as it did not happen on longer ride away from home.

Tried to tighten it with hand; had to redo 2x to home. Now; I am getting tools and something like loctite to fasten this thing. It is pretty annoying actually. Just trying to image if this would happen 30 km from home.

 

[e_1]

Hi everyone,
this is the fourth time the lockring has been coming loose.
In order I tried:
Used lockring new o-ring with grease 30Nm
Used lockring new o-ring with Loctite 30Nm
New lockring new o-ring with grease 30Nm
Steel lockring (selfmade on leathe) new o-ring with grease 30Nm
I have a torque wrench that works in both directions, so I'm sure about the tightening torques.
I'll try tightening the lockring to 45nm, in the worst case, if it doesn't hold, I'll have to throw the lockring away.

 

[RustyIron]

Have you opened up your Machinist's Handbook and looked at the torque tables?

 

[Bones]

It's a nut on an ebike. Nothing is fit and forget. Just keep an eye on it as over tightening Wil only stretch it.
It also won't need any grease as the O ring will deform too easily instead of just squashing.

 

[Paul Mac]

Don't use the O ring, you don't need it and I think this is the main reason it comes loose.
I've been running 3 different bikes over 4 years without the O ring never any problems and never come loose.

 

[Mikerb]

Hi everyone,
this is the fourth time the lockring has been coming loose.
In order I tried:
Used lockring new o-ring with grease 30Nm
Used lockring new o-ring with Loctite 30Nm
New lockring new o-ring with grease 30Nm
Steel lockring (selfmade on leathe) new o-ring with grease 30Nm
I have a torque wrench that works in both directions, so I'm sure about the tightening torques.
I'll try tightening the lockring to 45nm, in the worst case, if it doesn't hold, I'll have to throw the lockring away.

View attachment 135686

there is no need for grease on such a short amount of thread...........just make sure the thread is clean. At the end of the day if the lockring keeps coming loose I would guess the chain ring rather than the lockring is the problem.

 

[e_1]

Problem sorted:
Steel lockring
30Nm
O-ring
Grub screw with correspondent hole into the spider.