Mystery twang

[Andrew_Culture]

My single speed has developed an intermittent twang, the sort of noise you get if you've over-tightened a spoke. The wheels are very true indeed and there are no loose or tight spokes, and yet the noise seems to come from the rear of the bike.

There are no loose fixing on the bike (bottle cages etc).

There is nothing that I can spot that could twang against the spokes (cable ends etc).

The twang is worse on rough roads.

I'm fairly sure the chainline is straight, because I'm using a derailleur as a chain tensioner, so if the chainline ain't straight it flicks the chain off the rear cog.

The front crankset is very badly worn indeed (shortly to be replaced).

The wheels haven't been off this bike yet this year (god bless you Marathon Plus)

I'm a bit stumped!

 

[Christopher]

Like a sharp '"pang"? I had something similar to what you describe and it turned out to be the seatstays gradually breaking away from the rest of the bike . Frame eventually snapped. Not dangerously but it wasn't nice.
Edit: over in Know How there's a similar thread with twangs:
http://www.cyclechat.net/threads/cracking-snapping-crunching-cranks-transmission-any-ideas.122665/

 

[Andrew_Culture]

Photos

 

[Peter Armstrong]

Maybe dirts got in to the crank or wheel thingi and it builds up make the noise when it moves? happened to me

 

[thegravestoneman]

Sounds a bit like your chain to me, the chain on my butchers bike does it occasionally just re-aligning itself and getting caught. it has an extra duty chain to fit the front chain ring but goes over a standard sturmey archer sprocket at the rear giving it a bit of lateral play. Probably isn't this but just a thought..

 

[thegravestoneman]

also are your rear bearings ok? I assume the derailleur/tensioner is locked in both ways

 

[Andrew_Culture]

Maybe dirts got in to the crank or wheel thingi and it builds up make the noise when it moves? happened to me

Those spacers aren't incredibly tight, so could be possible.

 

[Andrew_Culture]

Sounds a bit like your chain to me, the chain on my butchers bike does it occasionally just re-aligning itself and getting caught. it has an extra duty chain to fit the front chain ring but goes over a standard sturmey archer sprocket at the rear giving it a bit of lateral play. Probably isn't this but just a thought..

That sounds entirely plausible, I've just changed the rear wheel and switched from using a dedicated single speed sprocket unit to a converted freehub with a sprocket that looks like it might be thinner than the previous cog, so it could be twanging into place occasionally. Is this the sort of thing that can lead to other things?

 

[Andrew_Culture]

also are your rear bearings ok? I assume the derailleur/tensioner is locked in both ways

I think these wheels have a sealed bearing unit. The derailleur is locked down so has no left or right movement.

 

[ianrauk]

And there was I thinking this was one of 3BM's threads about country and western music

 

[Andrew_Culture]

I'm going to grease the seat post and go out for a quick razz.

 

[thegravestoneman]

That sounds entirely plausible, I've just changed the rear wheel and switched from using a dedicated single speed sprocket unit to a converted freehub with a sprocket that looks like it might be thinner than the previous cog, so it could be twanging into place occasionally. Is this the sort of thing that can lead to other things?

It doesn't seem to cause follow on problems, both my chain and my rear sprocket seem to be in fine fettle although they are probably both a tad more heavy duty than yours. Other then checking it when you clean and oil it I shouldn't be too worried. famous last words I know. When you swap your front ring it may well stop as a new one will hold it a lot straighter.

 

[fossyant]

Those crud guards can be incredibly noisy !

 

[dan_bo]

A twang? oooh a twang I dunno what that could be. If it was a spaLUNG then I'd be able to help, but twang? sorry no.

 

[Andrew_Culture]

Those crud guards can be incredibly noisy !

Nah, that's much more of a thrubbbbb noise when they're not set right