h_curtis

I have a feeling my bottom bracket has a possible issue, but not sure. Wondering where to start. When I pedal under load I have a sort of clunking noise that is in sync with my pedal stroke and not in sync with my rear wheel. This is a new noise. It is most pronounced when under mild load. If I am under super heavy load it seems to be less. No load, very little. Kind of odd. Any ideas? Thanks.

oldiebikes

Could be as simple as a couple of spokes rubbing together. Under no load, it would be silent. Medium load would bring on a rhythmic thud sound.

h_curtis

The noise is at the top part of my pedal stroke when my right foot is coming up to the crest. Generally, that would mean the load would decrease a bit in that weaker part of the stroke. I try and make the stroke as smooth as I can and it is still there. This isn't something that has been an issue in the past, so it can't be me creating it entirely. I will check the spokes, but would they make that noise at the same spot as my pedal stroke every time?

JohnDThompson 

"In sync" with the pedal stroke suggests this is not an issue with the spokes or wheel. Bottom bracket and/or pedal bearings may be the source, or perhaps even excessive chain tension.

h_curtis

Thanks, this makes sense. I just checked chain tension and it is okay throughout the cycle. I felt the pedals and feel they are okay. I have a pretty strong feeling it is the bottom bracket. Time to research how to fix it. Been a very long time. Thanks again.

h_curtis

1. No chain issue.
2. Changed out pedals and that didn't help.
3. Made sure everything was tight. No help there.

I guess I am down to the bottom bracket. Thanks again for the help. Heading to a shop tomorrow and going to take it apart. Can't remember if it is a rebuildable one or not? It is older.

Asi

Is the chainring centered? On my clunker beater city bike (fixed) I have a slightly bent axle on the BB and that makes the chainring have a radial runout that in some position the chain is too tight and other too loose. (I ought to fix it but finding a proper cotter BB axle is tricky and since it's a beater, i really don't care to much. the chainline is good and had not fallen off at anytime)

On this bike that I mentioned, depending of chain tensions (position of pedals) it rings something (the chain too loose) or dead silent (chain is tight). Also the BB is a bit pitted and makes a tick at every crank revolution and due to cotter pins it makes a squeak at every revolution while pedaling hard. (same thing can happen on square taper but that indicates a badly worn interface while on cotter pins it's relative normal from a softer pin and repeated rub between crankarm and spindle while flexing the pin and is somewhat normal and does not indicate real damage to crank or spindle, maybe only a worn pin with a "stepped" taper on it due to wear)

h_curtis

My chain does tighten and loosen throughout the full rotation, but I just thought that was normal. Are you saying that if the BB is slightly off, that is the cause?

Oddly, this noise wasn't there last night. I think I am going to replace the BB regardless, if I can get a replacement. I don't mind putting some money into my daily driver and the money I save not driving more than makes up for the cost.

Asi

Yes, a bent BB axle is nasty on a fixed er, even single speed. But most often radial runout is caused by the chainring-crank assembly bolts. The bolts are not a tight fit, and while you put the chainring on the crank it can move a bit, while tightening the bolts, make sure the chainring is centered on the cranks.

Cpt Bike, Sheldon Brown, has an article about that, as you may know, he was an avid fixed gear rider. https://www.sheldonbrown.com/singlespeed.html#tension

Same problem may come as I said from a bent BB axle but that is somewhat rare.

h_curtis

I like that tension help, thanks. I am thinking I will change out my BB. I know they still make a Campy Chorus BB, but I don't know my size yet. My bike is a '80's track bike. Mine is a rebuildable one, but the races may not be great. Not sure.

h_curtis

Okay, I wanted to update this incase someone is doing a search on this noise. I took the BB apart today and found it was a very old sealed unit and isn't a rebuildable one. The guys shop I was working in who has been around these bikes for probably 45 years said, he never saw a sealed unit that old. Anyway, that really wasn't the issue. It was the crank side, which is more in a fixed position was ever so slightly loose. Under load it would move just a bit and when my right pedal was on the downstroke it would make a clunk type noise. He said that is pretty common on the right side. I tightened everything up and no more problems so far. I have a feeling it is fixed for now, but I may need to replace that old BB at some point. I took measurements incase I need to replace. They are 116-117/ 70. I believe that is still available.

Thanks for all the suggestions. Seems the first thing to look for if you have a noise on the downstroke of the crank side is make sure that is tight, which requires taking it apart and tightening it.