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Strange noise under load after full service (Bosch Performance CX)

pagheca

pagheca

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Hello everyone,

Long time since my last visit here...

After sitting for several months in a shipping container because of an international move, my Trek Powerfly 7 finally got a full tune-up last Saturday. Good thing I did — the chainring bolts were about to back out from the motor axle, a few screws were loose, and the tires were completely shot, so I swapped them for tubeless MAXXIS.

Since the service, though, I’ve been hearing a loud “RRRR… RR…” grinding noise on every pedal rotation when I’m putting a lot of torque on the pedals uphill. The motor is a Bosch Performance CX, and it’s never done that before. Has anyone else run into this? I’ll reach out to Bosch support, but I wanted to hear some real-world feedback first.

Thanks!
 
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I wonder if the motor bearings have developed some rust after sitting for such a long time. Moisture or water ingress? Suspending your bike and turning the crank/motor may isolate the noise. Different torques may produce different sounds also.

Loose chainring, castle nut, motor mount brackets, motor mount bolts (6), could cause those strange sounds.
 
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I recorded a video of the noise. Anyone should be able to see it with this link:

https://youtube.com/shorts/_fm5GLGxisQ?feature=share
  • it happens only when high torque is applied to the pedal (strong slope uphill)
  • unlike I was thinking, it looks like is not syncronized with the pedals rotation
Any comment... suggestions... ideas?
ncs said:
on strong torque it make such grinding RRR noise.
Click to expand...
They haven't replied the chain but this is exactly the symptom...
 
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that's funny, I let someone else check and it works. I don't know what else I can do about that... :cautious: but thanks for trying.

Does someone know of any other platform where I can upload the short for free AND anonimously?

However, maybe is not the motor to cause the noise but something else. Unfortunately it is not easy to check the source while pedaling uphill. More to come, hopefully.
 
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Ok I'm locked into this thread now so here goes.....
The vid now plays and it doesn't seem crank speed related.
The noise seems to occur at different points in the rotation.....unless I'm experiencing some wicked buffering delay issue :rolleyes:
Thats not to say its not a motor issue but I would of thought if it were the main bearings (first things to suspect) it would sound at the same point in the rotation...phew thats a lot right there.
have a look at anything else Chainring, mudguards. luggage, bags on the bike etc. Does it happen in every gear. Turn it upside down and turn the pedals. Get a mate to ride past you, anything's worth a shot. Do it :LOL:
 
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Thanks a lot for your suggestions.

I will try to take some pictures/video. Not easy to check because it doesn't happen when the bike is riding normally (flat terrain, no big torque applied to the crank).
 
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I watched and heard the video. This sounds very familiar to me. Not the motor, crank, or usual suspects.

It was the tire rubbing on the fender. Only when torque was applied the sound could be heard. The rear wheel would slightly twist during peddling (topical) and the nobbs of the tire would touch the fender (slightly) but make that same noise. The sound/noise was intermittent because the roundness of the wheel, and or tire, is not perfect. Applying torque is enough to push the wheel into the fender causing that noise.

Anyways, my mystery was solved. 🤷🏼‍♂️. It only happens occasionally now and I just bump or realign the fender. Since then I have slightly trimmed the plastic fender.
 
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If you find that it is tire rub (hopefully), check for spoke tension or correct wheel alignment. Some/most wheels are slightly off-set. The length of spokes will be different length's for either side. The centre of your tire can be changed with different spoke tensions. 12 speed, 11 speed, or 10 speed cassette’s can all be different. (Just some more ideas)
 
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Stihldog said:
I watched and heard the video. This sounds very familiar to me. Not the motor, crank, or usual suspects.

It was the tire rubbing on the fender. Only when torque was applied the sound could be heard. The rear wheel would slightly twist during peddling (topical) and the nobbs of the tire would touch the fender (slightly) but make that same noise. The sound/noise was intermittent because the roundness of the wheel, and or tire, is not perfect. Applying torque is enough to push the wheel into the fender causing that noise.

Anyways, my mystery was solved. 🤷🏼‍♂️. It only happens occasionally now and I just bump or realign the fender. Since then I have slightly trimmed the plastic fender.
Click to expand...
actually that was my very first guess, also because the new MAXXIS tires they installed are slightly wider than the original bontrager (but still within specs for this ebike). Maybe that under acceleration plus slope the additional load on the back slightly changes the geometry.

I will check again tomorrow morning... thanks everyone again! Very helpful comments from all of you....
 
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pagheca said:
Hello everyone,

Long time since my last visit here...

After sitting for several months in a shipping container because of an international move, my Trek Powerfly 7 finally got a full tune-up last Saturday. Good thing I did — the chainring bolts were about to back out from the motor axle, a few screws were loose, and the tires were completely shot, so I swapped them for tubeless MAXXIS.

Since the service, though, I’ve been hearing a loud “RRRR… RR…” grinding noise on every pedal rotation when I’m putting a lot of torque on the pedals uphill. The motor is a Bosch Performance CX, and it’s never done that before. Has anyone else run into this? I’ll reach out to Bosch support, but I wanted to hear some real-world feedback first.

Thanks!
Click to expand...
Sounds like a tyre rub.
 
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I can now confirm that the noise definitely comes from the rear mudguard, but I’m not sure how to fix it other than removing the mudguard itself, that wouldn't be very good for my clothes...

It has actually gotten worse today. It was pouring rain this morning, and the noise was almost constant while riding.

I’m attaching a photo for reference.

1763368339990.png
 
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pagheca said:
I can now confirm that the noise definitely comes from the rear mudguard, but I’m not sure how to fix it other than removing the mudguard itself, that wouldn't be very good for my clothes...

It has actually gotten worse today. It was pouring rain this morning, and the noise was almost constant while riding.

I’m attaching a photo for reference.

View attachment 171195
Click to expand...
10 points to me for guessing correctly!
 
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pagheca said:
I can now confirm that the noise definitely comes from the rear mudguard, but I’m not sure how to fix it other than removing the mudguard itself, that wouldn't be very good for my clothes...

It has actually gotten worse today. It was pouring rain this morning, and the noise was almost constant while riding.

I’m attaching a photo for reference.

View attachment 171195
Click to expand...
It's an easy fix
Fit a narrower tyre..
 
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Weeksy said:
It's an easy fix
Fit a narrower tyre..
Click to expand...
I prefer to look for a better alignment between the mudguards and the wheel axis because it touches the tire on one side only. The tires are brand new MAXXIS, much better than the original ones. I don't want to throw them away...
 
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Before I discovered that there was a specific rear fender available for my model of bike, I modified a front Monkey Nutz fender for the rear tire. The main reason was to protect the main pivot. A small rock was crushed in this area and caused slight paint chipping and a horrible noise. I needed some protection.
(Can’t post a pic🤷🏼‍♂️ For some reason).

I had to drill a few extra holes and trim the plastic fender for a good fit. Mounting the fender to the chain-stay triangle was critical. I didn’t want to damage the paint at the anchor points so I wrapped soft Velcro strips around those anchor points before I used zip-ties to secure the fender.

That looked good but didn’t sound good when I applied torque to the rear wheel. I could hear a rubbing noise from the nobbs of my Maxxis Assigia 29”x 2.6” tire while I was climbing. I carefully trimmed the plastic fender in that location.

Now I rarely hear that noise and the fender serves it purpose.
 
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