random knocking clunking sound

[campagman]

Have a horrible noise coming from somewhere on my fixed wheel work bike which I am struggling to locate the source. It is random and not in time with the wheels turning or pedals turning, sometimes quite loud other times not. I suspect the chain as I know that to be maybe a couple of years old. Can somebody tell me if this could be a typical of an old/worn chain on a fixed wheel bike? The bike was rebuilt last year, has a sealed B/Brkt which is not too old but does have an old rear wheel which could do with replacing.
If I lift the rear wheel and turn the cranks then there is no noise so only happens when ridden and a load is being transmitted through the transmission.
I know that really you have to listen to know what I am on about but would appreciate your ideas. I have never had a sound like this on any of my other bikes so I feel that it could be typical of a fixed wheel.

 

[betty swollocks]

Noises are maddening when trying to locate.
My first instincts go with bearings. How do the wheels feel when taken out of the frame and spun? Any roughness or anything feel loose?
Next, spin the cranks without the chain on. Does that feel smooth: anything loose there?
Headset smooth: not too loose or too tight?

 

[mickle]

Sounds like a ball has fragmented and is busily devouring the bearing surfaces of your rear hub.

 

[rustychisel]

unfeasibly large bollocks?

 

[John the Monkey]

Campagman, I like Sheldon Brown's guide to tracking down noises for sorting this kind of thing;

http://sheldonbrown.com/creaks.html

 

[campagman]

Thanks for the suggestions I will check out the bearings at the w/e. I have been fooled before by a creaking noise that I thought was coming from the B/B on another bike. It was only when I realised that the noise could not be heard when riding out of the saddle that I realised that the saddle clamp bolt needed tightening.

 

[domtyler]

Don't mean to frighten you but it could be your frame is cracking somewhere and you will only find out when you get a catastrophic failure sometime when you are turning in front of a lorry.

 

[campagman]

I have thought about the frame but with I would have that a noise like this would have caused a failure by now.
Anyway, I had a look at the bearings today. The BB was turning sweetly but the back wheel did feel a bit rough. I took it apart expecting to find a crumbling ball or two but the only problem that I could find was it was rather dry (no grease). I cleaned the races, packed it full of grease and put the balls back in and reassembled the axle. I thought that maybe it's not a bearing but something else. I rode the bike around the block to see if there is any noise and all was running fine.
I can't really see how a poorly lubricated hub would make the noises that I was hearing before but it looks to be solved now, well for the time being. I have always suspected the chain and I know that after I reassembled everything the chain was slightly looser than previous.
Regreasing the bearings is a job that I do rarely but it actually did not take too long. I will try to do it more regular from now on. Thanks for your suggestions.

 

[rustychisel]

next time you pull the rear wheel spin the axle carefully and inspect for any evidence of a bent axle, which is likely to produce the sort of sound you mentioned. If the axle is bent (not uncommon with older screwed hubs) it will eat your bearings and cones quite happily. A replacement axle will cost a couple of quid and can be hacksawed to length but make sure you match up the threads.

 

[rustychisel]

PS: dry bearings as you describe can back up against each other a little rather than be spread evenly around the race, causing a bit of a tidal effect, due to 'sticking' effect of old grease. Particularly so where it was common to use 10 balls a side rather than pack 11 into the race. The effect is almost imperceptible, but can be very noisy.

 

[campagman]

I replaced the axle a couple of years ago, so I would not think it to be a problem . I had to use a 10mm axle rather than 3/8" but it works ok and will be fractionally stronger. Thanks for the explanation about the dry balls, that could explain what I saw. I have had no problems with those noises this week.

 

[gkerr4]

the random knocking clunking sounds from my bike are from my left knee.

I need an arthroscopy to repair a meniscal tear

:-(