Sympathetic vibrations (noisy motor)

[Haku]

At certain speeds the back end of my bike amplifies the vibrations from the motor and it sounds pretty loud, is there any way to detect what's sympathetically vibrating and stopping it?

 

[BGElect]

Not easy I suspect. I read a recent motorcycle review that had vibration through the footpegs that a very similar version of the bike didn't and it came down to the foot peg hangers acting as a tuning fork in sympathy with the engine, only fix was a redesign of the footpeg hangers

 

[flecc]

As BGElect says, not easy, and it's usually a trial and error thing.

Adding weight to suspect items can change or get rid of the noise and identify the culprit. An alternative is adding tension to do the same.

For example, if the mudguard and stays are suspect, a piece of steel of any sort can be taped onto a stay or the mudguard. Alternatively, a bungy can hooked onto the mudguard or a stay and stretched to a frame point to apply tension. If the sound changes or disappears, you are on the right track to the source.
.

 

[Blew it]

Spokes!

I suspect it may be the spokes. I had a similar problem once, which was cured by having the wheel trued. The gent that carried out the work remarked on how slack the spokes were.

Regards

Bob

 

[Steveb63]

Hi Haku

I tracked down an annoying rattle on my bike using a large blob of blu-tak -easy and worked a treat!

Steve H.

 

[UrbanPuma]

Hi Haku,

One possible cause could be the motor wire coming loose. You may want to check the connection to make sure as this could happen if the wheel has been removed to replace an inner tube for example.