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Weird noise coming from bottom bracket area
#1
Ok, so recently I was out mountain biking and as I was climbing a steep section of the trail, my cranks felt like they skipped a few teeth on the gears or something slipped, as they spun but didn't move the back tire any. I checked the gears on the front and the cranks and everything looked fine. I checked the cranks and they were tightened all the way. However when I've been riding lately on the road, there is this sound that sounds like metal hitting metal and it's coming from the crank/bottom bracket area. It only happens when I'm riding hard and speeding up, once I get going it stops making the noise. Anyone know what this might be? I live in a rather remote area, so I have to order everything and I'd rather find out what the problem is before I order something. Thanks.
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#2
Hi

To be honest mate a weird noise is extremely hard to diagnose, especially over the internet. It could be a worn crank interface, a worn BB, or simply the chain clipping the front derallieur when you mash the gears.

I would recommend you do a chain wear check (there's a video guide on the site), as if it's worn that could be causing the chain to slip.

creaking noises from the BB could be any of the above, or the bb is simply full of mud, dust and gunk. Take the entire BB, cranks, etc. off and clean all the threads and grease properly on installation. Also check there's no play in the BB by trying to flex the cranks. If none of these are the culprits then you're going to have to look elsewhere (my mate had a similar problem, but it was actually the headset that had worn out, and the noise transmitted itself around the frame so it sounded like it came from the BB.
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#3
I had this problem too, could be water in the bottom bracket, worn bearings, rust, or lack of lubrication, my LBS said i needed to get a new one, my solution?
stick it in a oil/wd-40 mix overnight. Run smooth as new.
Worth trying this, i'm not sure if it'll cure yours though.
Chuck Norris actually died 20 years ago, death just hasn't built up the courage to tell him yet.
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#4
(10-13-2010, 04:14 PM)nameused Wrote:  ... when I've been riding lately on the road, there is this sound that sounds like metal hitting metal and it's coming from the crank/bottom bracket area. It only happens when I'm riding hard and speeding up, once I get going it stops making the noise. Anyone know what this might be?...

I had the same problem just last week. I use a Shimano Alivio crankset with an octalink BB. Just put my new bike together last December, and I've only been using my bike on paved roads, so unlikely that my BB bearings were damaged or worn out already, right. It started as a clicking sound that was in synch whenever I bear down on the left pedal. Then the next day, a bit of creaking started to mix in with the click. Then a day after that, the click became a knocking sound -- the harder I pedal, the louder the metal-on-metal knock. At first, I thought it was the left crank arm becoming loose -- so I tightened the screw to eliminate any creak. That didn't do anything. Next, I thought maybe the left pedal was faulty (new as it may be) -- tried replacing it with an older pair which came from my older bike. No good. Lastly, I sprayed a bit of chain oil into the leftside lock ring of the BB -- the knocking sound slowly devolved into clicking, until it totally went away after another day.

This week, I decided to take off my cranks & its BB. I just finished cleaning out the inside of the BB tube -- there's a lot of rust on the dependent/bottom area of both BB tube & BB cartridge casing! WTF, I don't know how that happened (I've never biked with my BB tube / crank submerged in water). Maybe some water found its way from my under my seat, into the seat tube, and down into the BB tube on days that I biked in the rain. Anyway, I had to clean the rust out with WD-40, after which I spread some gear grease on the inside of the BB tube & on the body of the BB cartridge. Put some grease on the threads/lockrings as well, just to get a bit of water seal. So far, no more funny sounds.

Hope this works, should you try it. ^_^

[PS -- I wanted to do it like what harrylucas said, just leave the oil I sprayed into the lockring thread alone. But I figured that, should the oil eventually settle or seep out, I might get that knocking/creaking again. Which is why I decided to fieldstrip the cranks & BB, clean out the BB tube, and re-seal. I hope the grease works as predicted.]
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