spokewrench
Active Member
- Region
- USA
My Aventon Abound was two months old when I began hearing a brushing sound from the bottom bracket each time the right pedal passed 5 o’clock. I figured it must have happened to others, and Support could advise me. They said they couldn’t help me if I wouldn’t send them a photograph of the noise. You can’t get blood from a turnip.
The next day, it was embarrassingly loud. The day after that, there were two brushing sounds per revolution, at 1 o’clock and 5 o’clock of the right pedal. The right bearing handles the chain load. It also handles the load from the right pedal. The brushing sound was occurring during the transition, when the combined load was going onto the bearing and when it was coming off.
Ball bearing manufacturers say that when the load is not at least 1% of the rated load, the balls may slide instead of rolling, causing rapid wear. In bicycles, a bearing isn't unloaded long enough to run dry. A film of lube would probably make sliding inaudible. If I could hear it, it might mean my bearings were sometimes running dry.
The bearing was silent for three days. When the noise returned, I realized the temperature had been above 60 for those three days, and now it was cooler. I used a hair dryer to warm the bottom bracket to 62 degrees. The noise went away.
It seemed that below 60, the lube was too stiff to keep the races and balls lubed. There had been no problem December and January, so it seemed that the lube was getting stiffer. Normally, manufacturers of sealed bearings take care to use greases that maintain their original consistency.
I bought tools to remove the right crank arm and the chainwheel. The bearing appeared to have a rubber seal partly covered by a steel shield. I bought a bottle of synthetic oil with a 19 gauge needle, used a hand drill to make a 1/16 inch hole, and injected what was probably less than a gram of oil, hoping to thin the grease enough to keep the races lubed.
For weeks it was quiet at all temperatures. It came back worse than ever, even when the bottom bracket was at 75 degrees. I pulled off the chainwheel and found that what I’d thought was a shield was a clip that could be pried out with small screwdrivers. What I’d thought was a rubber seal was a rubbery coating on a soft metal washer.
I couldn’t get the balls out, so I wiped off what grease I could as I turned the shaft. Then I packed the available space with Lucas Red ’n’ Tacky. That was several days ago, and there has been no more noise. I noticed something else. There's a 5% hill near here that I can climb without assistance on a single-speed ebike at 86 gear inches, but on my Abound, even if I shifted down to low, 37 gear inches, I’d get tired and turn on PAS. With the Red ’n’ Tacky, I don’t need PAS. Before, when I felt a headwind on my face, pedaling would get hard and I’d need PAS. Now I don’t.
The left bearing has a smaller load and smaller duty cycle than the right, but it, too, may have substandard grease. I guess the next step is to get to the controller so I can unplug the PAS wire and remove the bottom bracket to see if I can repack the left bearing. With the bottom bracket out, I may also be able to clean out the right bearing better.
If my bottom bracket torque sensor had bad grease, maybe they all do. I’ve seen three topics about 2023 Aventons where pedaling began to drag when they were a few months old. Maybe their bottom brackets need better grease. None mentioned a brushing sound. If they were riding faster or off road, maybe they wouldn’t notice, or maybe stiff grease didn’t cause the sound because they pedaled differently.
The next day, it was embarrassingly loud. The day after that, there were two brushing sounds per revolution, at 1 o’clock and 5 o’clock of the right pedal. The right bearing handles the chain load. It also handles the load from the right pedal. The brushing sound was occurring during the transition, when the combined load was going onto the bearing and when it was coming off.
Ball bearing manufacturers say that when the load is not at least 1% of the rated load, the balls may slide instead of rolling, causing rapid wear. In bicycles, a bearing isn't unloaded long enough to run dry. A film of lube would probably make sliding inaudible. If I could hear it, it might mean my bearings were sometimes running dry.
The bearing was silent for three days. When the noise returned, I realized the temperature had been above 60 for those three days, and now it was cooler. I used a hair dryer to warm the bottom bracket to 62 degrees. The noise went away.
It seemed that below 60, the lube was too stiff to keep the races and balls lubed. There had been no problem December and January, so it seemed that the lube was getting stiffer. Normally, manufacturers of sealed bearings take care to use greases that maintain their original consistency.
I bought tools to remove the right crank arm and the chainwheel. The bearing appeared to have a rubber seal partly covered by a steel shield. I bought a bottle of synthetic oil with a 19 gauge needle, used a hand drill to make a 1/16 inch hole, and injected what was probably less than a gram of oil, hoping to thin the grease enough to keep the races lubed.
For weeks it was quiet at all temperatures. It came back worse than ever, even when the bottom bracket was at 75 degrees. I pulled off the chainwheel and found that what I’d thought was a shield was a clip that could be pried out with small screwdrivers. What I’d thought was a rubber seal was a rubbery coating on a soft metal washer.
I couldn’t get the balls out, so I wiped off what grease I could as I turned the shaft. Then I packed the available space with Lucas Red ’n’ Tacky. That was several days ago, and there has been no more noise. I noticed something else. There's a 5% hill near here that I can climb without assistance on a single-speed ebike at 86 gear inches, but on my Abound, even if I shifted down to low, 37 gear inches, I’d get tired and turn on PAS. With the Red ’n’ Tacky, I don’t need PAS. Before, when I felt a headwind on my face, pedaling would get hard and I’d need PAS. Now I don’t.
The left bearing has a smaller load and smaller duty cycle than the right, but it, too, may have substandard grease. I guess the next step is to get to the controller so I can unplug the PAS wire and remove the bottom bracket to see if I can repack the left bearing. With the bottom bracket out, I may also be able to clean out the right bearing better.
If my bottom bracket torque sensor had bad grease, maybe they all do. I’ve seen three topics about 2023 Aventons where pedaling began to drag when they were a few months old. Maybe their bottom brackets need better grease. None mentioned a brushing sound. If they were riding faster or off road, maybe they wouldn’t notice, or maybe stiff grease didn’t cause the sound because they pedaled differently.
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