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Strange sound near the bottom bracket (BB) area

Old 09-15-20, 02:44 PM
  #1  
torony
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Strange sound near the bottom bracket (BB) area

Hi there,

I own (first owner) a Giant Escape (city/hybrid bike) which i use for fitness purposes equipped with Shimano BB-UN100 cartridge bottom bracket for square taper cranks. I already rode it for 5500 km and im hearing recently a weird sound coming from the BB area ONLY when pedaling on mid cadence level (not when the pedals are under high load). The sound is not continuous and one cannot predict when it will occur. What im sure of is that you will not hear it if you are simply turning the pedals when the bike is stationary (i.e. lifting the rear wheel and turning the pedals by hand), and you will hear the sound 3 times when it is there (i.e you will hear "tak" tak" "tak" then no more sound), Took it for inspection and the shop told me that the BB bearings (model reference: 6903 RS) need to be changed (1 was in a bad shape, the 2nd was good). After installing a new set, the sound remained and nothing changed. They are now advising me to change the whole BB saying that the spindle might be causing the sound.

My questions are:
1- What is the general lifetime of a bearing/BB/spindle knowing that i ride only on asphalted dry roads thus no water/mud residues on the bike except the road surface dust.
2- Is it possible that the BB will be damaged knowing that i/the bike haven't been engaged in any accident/direct hit on the spindle/pedals/crank area.
3- If the BB needs to be replaced, any recommendation on a model that might enhance/help in my riding performance, and what i should be looking for (in terms of dimensions) before buying a new one.

Cheers
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Old 09-15-20, 03:25 PM
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1. Check pedals first. Remove them and spin them in your hand. If gritty, replace or service the bearings. If smooth, grease the threads and re-install. The non-drive side pedal is reverse threaded.

2. Check that the crank arms are securely bolted to the BB spindle.

3. If you're dealing with the BB bearings, just pull the whole cartridge and replace it. I think those UN100s have plastic cups, and may be the source of your noise. I'd replace it with one that has aluminum cups. Pay attention to the bottom bracket width and the spindle length. Both numbers should be written on the cartridge. Grease it well when installing. Mine usually last a couple of years.

Test ride after each step until you isolate/fix the noise.
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Old 09-15-20, 05:14 PM
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Fahrenheit531 
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The quest to find a strange tick-tick-tick or creak or whatever has driven more than one cyclist to madness. A bicycle frame is great for transmitting sound and what you think is a sound from this might actually be coming from way over there. Like the time I overhauled a bottom bracket... (still there) ...then replaced the pedals... (still there) ...then eventually realized my saddle creaked when it was cold.

My point? Be patient. Don't fixate on a single possibility. Nothing is going to catastrophically fail while you figure it out.

Edit, to answer ar least one of your questions anyway: The time before a bb needs overhaul, under the conditions you describe, is far longer than 5500km.

Last edited by Fahrenheit531; 09-15-20 at 05:23 PM.
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Old 09-15-20, 05:27 PM
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Originally Posted by torony View Post
...weird sound coming from the BB area ONLY when pedaling on mid cadence level (not when the pedals are under high load).
See if you can reproduce the noise when standing out of the saddle. If you can't, it might be the saddle. That might be hard to believe, because it sounds like it's coming from the BB region, but it's happened to many of us - senses and intuition are erroneously suggesting it's the BB or crank, when the saddle is the culprit.
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Old 09-15-20, 05:46 PM
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Had three different situations in our family recently that all sounded like BB only when pedaling. One was a rear thru axle not tight enough. One was a seat post. One was a shoe cleat that just needed removed and cleaned. Eliminate the easy stuff you can do yourself before tearing into the BB. There are long wait times at the shop around here to get service.
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Old 09-15-20, 09:24 PM
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I recently had a sound similar to this on my gravel bike. It turned out to be the rear hub. The Pawls in the freehub were not fully engaging, and would cause a random tick or knock. I was convinced it was the bottom bracket.
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Old 09-16-20, 07:09 AM
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Had 2 similar issues somewhat recently.
  1. My pedals/cleats were the first one - Spring in the Speedplay cleats was sticking so I'd get these multi-click sounds every once in a while (put some dry lube in them and they were fine).
  2. A single cog in the rear cassette was having issues - Really thought this one was the BB and tried a million different thing before realizing the clicking sound only came on when in a single sprocket on the rear. Not exactly sure what it was but I took the cassette off, cleaned it up, put it back on and the sound was gone.
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Old 09-16-20, 07:15 AM
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Thread moved from General Cycling Discussion to Bike Mechanics.
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Old 09-16-20, 07:35 AM
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I tend to agree with Fahrenheit531 . It's unlikely things are going to catastrophically and dramatically fail. And likely that whatever is wrong isn't going to cost significantly more to fix when it does finally let you know what it is.

Do be aware and investigate possibilities when ever your think of a possible cause, but don't drive yourself nuts looking for it.

And if your bike shop mechanic didn't tell you it was just a guess about the noise when they dealt with it, then shame on them. Though I suppose coincidentally it might be that the other stuff was still needed at the time.

Last edited by Iride01; 09-16-20 at 07:38 AM.
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Old 09-16-20, 09:41 AM
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The guy who managed a shop where I once worked shared this advice on mysterious noises:

"Leave it alone. It will either go away on its own or get bad enough that you'll know exactly what's causing it."
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Old 09-16-20, 05:52 PM
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Moe Zhoost
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Originally Posted by Rolla View Post
The guy who managed a shop where I once worked shared this advice on mysterious noises:

"Leave it alone. It will either go away on its own or get bad enough that you'll know exactly what's causing it."
Yep, exactly right. My ticking sound ended up being a micro-crack in a crank arm. I figured this out as I was laying on my side on the ground watching my pedal slide across the road.
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