Glottis

Hi everyone,

There's a noise that is best described as a low frequency rolling sound. I pinpointed that it's coming from the chain rolling over the cassette or the derailleur rollers, no matter which cog it's on.

Spinning the chain backwards or forwards produces this sound. Also, changing the front gears doesn't make the noise go away, in case you're wondering about the chainrings making the noise.

I removed the chain and spun the cassette. It spins smoothly, and that noise can't be heard. Spinning the crankset without the chain on doesn't produce the sound either. The sound is not coming from the pedals themselves.

I noticed this sound a few months ago, I don't know if it was there when I bought the bike last year. All the parts are the original ones. I measured the chain, and it's not "stretched".

The sound itself isn't annoying, but I can feel that the "thing" causing it is wasting a lot of energy, so pedaling isn't very efficient.

Thanks for your help.

JohnDThompson 

Have you cleaned/lubricated the chain recently? If not, do so and report back.

DCB0

I had a similar problem for weeks. I looked closely at the derailleur and realized I had routed the chain wrong and it was dragging over part of the derailleur cage when it should have been passing clearly underneath it. Make sure the chain is routed properly, as a simple mistake like this is easy to make.

Glottis

Yes I did. The noise is there whether the chain is clean/lubricated or not.

The vibration can be felt if I touch the frame and saddle when the chain is moving. Maybe the chain isn't making "proper" contact with the cogs' teeth? This can happen when the chain is old and cassette is new maybe, but all the parts I have came with the bike. BTW, I did around 1500 km/ 1000 miles on this bike.

Glottis

The chain is routed properly.

tanguy frame

maybe it's just bad quality stuff? have you tried a new chain and cassette?

Glottis

I'll try an almost new chain tomorrow. My friend has the exact same bike, a Giant CRS2 2009, I checked it and his bike doesn't have such noise. Thing is, he has maybe 3 times more miles on that bike, and doesn't really take care of it. I treat my bike like a queen. I'll probably shoot a video tomorrow and will post it here.

tanguy frame

you shouldn't have to treat your bike like a queen. Reserve that for your girlfriend.

FBinNY 

Roller chains produce a characteristic low frequency whirring, or gentle buzzing. The frequency varies with speed, and is more pronounced with worn chains and sprockets, or when riding on non aligned sprockets. It's the result of small shocks as the chain picks up the teeth as it winds onto the sprocket.

All roller chains do it, which is why the peloton sounds like a swarm of hornets as it goes by.

gyozadude

If you have the chain removed, can you spin the rear derailleur pulleys? How do they feel? Smooth? Or tight? Rough? The bushings sometimes fails on derailleur pulleys and makes a grinding sound. The failure might still allow the pulley to spin fine under a light load. But you get a regular buzzing or grinding when chain runs through and the spring arm of the RD pulls chain tight. The other thing to check might be the rear axle bearings. With tightened QR, does the wheel spin for a long time or slow down fast? If you adjust cones out slightly until a tiny amount of play exists, and then retry the spin test with the rear wheel, does it spin longer now? Just a few thoughts.

Bachman

I am having a similar problem on most gears, but much worse on a few particular ones. I recently cleaned and lubed the chain, and I also added some lithium grease to the bearings of the derailleur pulleys. It started happening shortly after I did this. I can almost imagine the pulleys vibrating like crazy with each pedal stroke, as if they've reached some harmonic frequency. Driving me nuts. Maybe I put too much lithium grease?

Glottis

I really hope my wife doesn't see this thread. She'll think I'm not only into bike porn, but regular porn, too.

It's not just a gentle buzzing. It's a vibration caused by something that's briefly encountering some sort or resistance while it's moving, then sharply continuing. I don't know how to explain it better.

One of the pulleys is smoother than the other. The smoother one spins freely for about one turn after I let go of it, the other one doesn't. Nothing tight nor rough, though.

The wheel spins for a long time. And the vibration and noise aren't there when I simply spin the wheel.

Thanks for the suggestions everyone. Keep them coming!

Glottis

After a lot of trying and observing, I now know the cause of the vibration. But how do I fix this? The cassette teeth are briefly pushing the inner plates of the chain outwards, after which the chain snaps into place, causing the vibration and slight noise. In the following video you can see how the chain shakes from time to time. The noise can't be heard, and of course the vibration can't be felt in the video.

https://www.youtube.com/watch?v=1cSnLKXsOQ0

A photo is attached of how the cassette teeth touch the inner plates of the chain.

Why is this happening? Maybe the cassette is too tight on the wheel? How do I increase the distance between the teeth and the inner plates that are closer to the wheel?

FBinNY 

Read my post (#9). This is exactly what I said. Part of the problem is worn sprocket, but even if perfect the inner plates will touch the tips of the teeth when coming from an angle.

You have 5 choices besides replacing the worn freewheel. (which won't totally solve the problem)

1- file or grind more entry bevel on the sides of the teeth, so the points slide into the chain more smoothly. Look at your chainrings to see the difference. If you go this route, make sure to file on the offending side of the sprocket.

2- use a chain with more bellmouth or bevel on the inside of the inner plates, which act as a funnel to guide the teeth in smoothly

3- use a quality shocking absorbing oil, like Chain-L which doesn't actually change anything, but dampens the tiny impacts quieting the chain. (sorry for the cheap plug, but it's appropriate here)

4- go single speed, eliminating non-aligned sprockets entirely

5- live with it, it's a characteristic of derailleur bikes and will never go away entirely.

Glottis

FBinNY, I completely understand what you're saying, and I know it's normal at an angle. But should this happen on such gears as 1x1 or 2x4 on an 8 sp. cassette? The video above was shot with the chain being on the smallest chainring and largest cog.

On derailleur bikes, if the chain is on the middle chainring, on which cog should the chain be to obtain the straightest chainline?

I'm asking this because I'm starting to think someone messed up when installing the cassette. Maybe forgot a spacer or something?

FBinNY 

I doubt there's any missing spacer, the cassette is usually mounted as close to the frame as possible while allowing chain clearance. You can check the chainline quickly by laying a straight edge on a secant edgewise against the face of the outer chainring and carrying the line back. It should meet the cassette outside of centyer by an amount roughly equal the the distance from outer face to center of the gap on your chainring.

In any case, it isn't a matter of inline or not, but of degree. Any chainring can only line up with one sprocket, and with normal chainline the inner lines up just inside the center of the cassette, and the outer just outside center. After that all the sprockets are off line to a degree, getting worse as you move to the ends of the cassette. Cross chaining makes it that much worse.

BTW- note that in your video, you're running it backward, and the chain is actually coming off the sprockets in the real world. the engagement at the bottom is always smoother because the RD is feeding it in line.

If you read various threads you'll note that some systems including some of the most expensive have a reputation for being noisier than others. The key is the amount of bevel of the teeth, the amount of bevel on the inside plates, and the lube.

Don't look for a problem that you don't have, focus on making adaptations to address exactly what is happening. As i said it's normal and to a degree unavoidable.

Looking at your video it seems that your chain has very square plates, Many others have more bevel which lets the chain off easier, ramping off the teeth, rather than jumping off as they disengage. I suggest you try a new chain looking specifically for the model with the most bevel.

Also since the issue is worst on the innermost sprocket, try grinding a shallow bevel on the inside of the teeth, either freehand on a bench grinder, or with a Dremel, while turning the cassette (like a lathe).

You'll find that either or both in combination will make the drive train much smoother.

If you want to see how much difference the oil can make email me at my site below, and I'll send you a sample.

Glottis

Thanks for the detailed answer. I almost never use the innermost sprocket, I was using it as an example as it seemed logical to me that the chain shouldn't be at an angle when on a 1x1 gear.

I guess I'll know what to look for when it's time to buy a new chain.