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C400X clutch pulley failure

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sanoke

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I purchased a new C400X back in 2019. I have done all the recommend BMW servicings at the recommend mileages. At around 70,000 miles the CVT started making a noise like a wood chipper and I was losing power. I took the CVT cover off and didn't see anything obvious so I continued riding it until the 72,000 mile servicing in hopes that a new belt and rollers might fix it. That didn't do it so after watching a video of a mechanic running a C400X with the CVT cover off, I decided to do that myself. What I discovered when it was running was that the clutch pulley face closest to the clutch was wobbling badly. That convinced me that the clutch assembly was bad so I replaced it and that fixed the problem. I decided to try to figure out what went wrong so I put together a fixture using my drill press as a framework that allowed me to unload the spring and take the assembly apart (first photo). What I discovered was that the pulley face closest to the clutch engages with the inner face (which is the driven face) through four pins and rollers that run in grooves on the shaft of the outer face (second photo). What had happened over time was that the rollers, which are softer metal than the pins, had worn so the holes were now tapered instead of straight like originally. This allowed the torque applied to the rollers to push downward on the pins and eventually pushed the pins so far into the shaft that they no longer engaged the rollers. When that happened the outer face was now free floating and didn't provide any drive to the rear wheel so half the driving contact to the belt was lost. This allowed the belt to slip and it also allowed the face to wobble freely which made the noise.

So the moral of the story is that if you have a 2019 C400X with the original clutch, eventually this problem will happen to you too. I have figured out a way to visually check to see if you are close to having this failure. When the clutch assembly is off for a belt change, by turning it over and shining a light into the shaft you can see the pins coming through the shaft. I've measured the point at which the pins no longer engage the rollers and that is when they have been pushed into the shaft by 2.3mm. I found a piece of welding rod the was real close to 2.3mm and by using a flashlight and putting the rod next to a pin you can get an idea of how close to failing it is (third picture).

I do know that at some point the part number for the clutch assembly changed so BMW may have fixed this on newer model. Hope you find this information useful.

IMG_3320.webpIMG_3322.webpIMG_3328.webp
 
Hey, did yours make this noise as well. Mine is only about 3500 miles old. but I seem to have pinpointed the noise to the Driven pulley. I have taken the CVT cover off, but do not have a spanner tool nor a large impact to remove the big nut just yet to see further inside the assembly.


 
I apologize if I am spamming your thread. I don't seem to have any traction on my post and You seem to have some experience with Driven pulley. I found my issue once i got my spanner. The inner disk that the belt rolls on seems to have gotten some play in the center. I noticed some shavings on the back side. It looks to be loose just sitting there but I am not familiar with this whole assembly so I dont know if I can use the large nut that holds the assembly together to tighten it more or if this is a done deal. There does not seem to be any specific parts for this other than the whole clutch.

Attached is a Pic and a Video

 

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Good evening. I am the owner of a BMW C 400 X. For a while now I have been having a problem with the idle. As soon as I reach a traffic light the engine turns off. Has anyone encountered this problem? Thank you very much
 
monicos said:
Good evening. I am the owner of a BMW C 400 X. For a while now I have been having a problem with the idle. As soon as I reach a traffic light the engine turns off. Has anyone encountered this problem? Thank you very much
Click to expand...
@monicos :

1) You might want to read through this three-page thread from 2019 - 2022, as I think your problem seems more related to the issues discussed in that thread than in this thread (particularly if your C 400 X is an older model year). That is, you would probably be better off posting in this other thread:

G

Thread 'brand new C400X - stalls'

Proud owner of a brand-new C400X here - well not quite so proud since the thing stalls.

Seems that after a period of engine-braking only, drifting to a stop, if I don't get on the brakes in time to allow the clutch to release, or if I don't give the throttle a mini blip, then it can stall. Especially so if it's higher than normal engine braking - eg I can reproduce it best if I coast down the entrance ramp to my underground carpark and let it drift to a stop.

Very irritating since this is a brand new bike, I've got about 700 miles on it now. I took it into the shop early for its first...

2) Welcome to the forum. And don't forget about the SEARCH FORUM function, found atop most pages here.
 
ELvir said:
I apologize if I am spamming your thread. I don't seem to have any traction on my post and You seem to have some experience with Driven pulley. I found my issue once i got my spanner. The inner disk that the belt rolls on seems to have gotten some play in the center. I noticed some shavings on the back side. It looks to be loose just sitting there but I am not familiar with this whole assembly so I dont know if I can use the large nut that holds the assembly together to tighten it more or if this is a done deal. There does not seem to be any specific parts for this other than the whole clutch.

Attached is a Pic and a Video

Click to expand...
Looks to me like the pulley has come loose from the shaft. I'm afraid you are going to have to replace the unit.
 
I noticed that there is no option for replacing the plate but buying the entire clutch kit at $1000. I have no interest in that. I did inquire with a friend who rides scooters, and he suggested to just put a couple of weld beads to bind the two plates together. Anything worse happens, then I am in the same boat of having to buy the entire clutch kit. Any thoughts to that?
 
I was referring to tacking up the two aluminum plates together from the inside where the belt goes, but further closer to the center where there is a better chance of laying down a clean weld tack. I think for now, I will keep riding as I am not doing much these days with cold weather, but if i notice the noise is getting worse, then I will attempt the tack weld.

I am surprised that based on how many miles you have that you do not have that issue yet my bike only has ~3K miles and this issue is already present.
 
Just so you know, the way the CVT works is as the bike speed increases those two plates separate to allow the gear ratio to change. That's why that big spring is there. If you weld them together then as the front pulley comes together from centrifugal force you are going to put a lot of stress on the belt because the back pulley can't separate.

I suspect you have a manufacturing defect. I have two C400X bikes. Both have had defects that caused different kinds of failures.
 
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