Engine noise question

[raymr]

It seems at certain times while accelerating or partial load around 3000 RPM there is a buzzing dragonfly kind of noise coming from around the engine. I'm wondering, is it a normal engine sound or is something on the frame rattling? Most everything has new rubber bushings and mounts. The valves were adjusted but I didn't check the sideways clearance. Could that be a cause?

[Bob_Roller]

There is a vibration band that's pretty common with the R65, usually it's in the 4000-4500 rpm range .

It's usually a buzz type vibration and it usually starts like someone turned a switch on .

Not sure if this is what you are experiencing or not .

Only other suggestion I can give, is to look the bike over real good, something may have come loose .

Check things like the center stand and side stand vibrating on the exhaust, etc....

[tvrla]

Noises like that can travel and come from anywhere. It might be from under the tank - maybe one of the cables vibrates at that RPM and rubs on the underside of the tank? Maybe a muffler mount is loose? It could be anything. A detailed search is about all I can recommend. And, no, vibrations, rattly noises, buzzing, aren't normal sounds.

[Barry]

When I had a noise at those revs it was something causing the tank to vibrate.  I could feel it through my knees. Cables bunched on the left side of the frame top tube had very little clearance so I did a general tidy up with cable ties and jacked the rear of the tank up a touch with new rubbers. That cured it.

[raymr]

I'm 90% sure its valve train related. Its more of an amplified clattering version of the usual ticking, and it comes in at 2800 RPM and goes away again at 3000 RPM. It only happens while driving, and happens in every gear. I cannot reproduce it standing still and revving in neutral.

The gas tank has good rubber isolation all around, so its not the tank itself. I'll check the cables and such that run underneath it.

I'm having a hard time describing the sound - like a large flying insect or like a playing card flapping on bicycle spokes.    

[bruce_launceston]

At those lower revs is the engine under load, slugging along, or is the buzzing with it revving freely?

[raymr]

Its either while accelerating or decelerating, not necessarily lugging. Last night I found an air intake snorkel on the air cleaner isn't attached solidly, so I'll check that today if it warms up.  

[Barry]

At 2800 - 3000 RPM you are just on the first minor vibration period. All airheads have a slight amount of vibration at approx. these revs which is usually insignificant and hardly noticed but it might be enough to incite vibration in something else like the tank. In other words if the tank is going to vibrate it will do so at these revs.

[tvrla]

Engines are funny that way too. I remember the older Volvos I used to have - at 60mph they'd sound like they were straining, running rough and noisy. But get up to 70 or 75 and they'd quiet down and act like it was all effortless and could continue forever.

Engines are designed with a particular RPM band in mind, and everything just works right at that point. But at some other RPM bands things don't come together so well, harmonic vibrations don't cancel or whatever factors are involved, and things are just 'off'. These boxer engines have a band right around 3K and another around 4K where vibrations and clatter are magnified.

It's possible that's what you're experiencing.