Vibration reduced by engine guards?

[keithu]

I installed the Hepco & Becker engine guards last weekend, and it seems like the high frequency vibes between 4-5k RPMs are reduced. Am I on crack, or is this possible? I certainly wasn't expecting it.

[adjuster]

Very possible. You made the whole bike stronger. Also the stock bolts might have been loose?
 
The engine is a stressed member of this design, as are almost all modern bikes and some cars now days too. (Especially race cars.)
 
Add more metal, and you change the structure, and that changes dampening effects, but not the cause of the vibration or harmonics.
 
Would be really cool to try and isolate some NVH (the tech term for this, Noise Vibration and Harshness.) with rubber or urethane washers, adding mass to the bars, or suspending mass in oil inside them. Many cars today have mass dampening devices to cure various NVH issues to make the car quieter, or resolve a buzz/noise/shake that was being created by the engine/transaxle etc.
 
I used to train Claims Adjusters how to diagnose damage to them, and replace them if needed, and why they were important to replace, since the car would have issues if they were broken, removed or not replaced.
 
A great way to dampen buzzing hand grips is to fill the bars with lead shot. Works great, but with the stock bars, remember that you have holes drilled in the bars, and smaller lead shot will leak out those holes. Using BB's is another fix, and they don't leak out the bars as easy, too big for most holes. Bet if you filled the Becker bars with lead shot, they would further dampen the vibes in this bike?
 
Cool experiment if you have led shot, and time to experiment. (And assuming there is a hole you can dump the shot into the bars...)

[desertfjr]

Another potential result of the engine guards is that the energy that used to buzz the bars is now vibrating the H&B, dissipating the energy or creating a cancelling frequency at the RPMs you reference.

[keithu]

That all makes sense. The H&B bars don't have holes. Filling the handlebars might be interesting, but it might also reduce the effectiveness of the heated grips by making the bar a stronger heat sink.

[bruceintucson]

Another thing that might have occurred is that by loosening/replacing the engine mounting bolts you created the correct torque or torqueing sequence for the engine bolts. Many bikes have an actual procedure & tightening sequence for the engine bolts. And one trick talked about a few years ago on the FZ 1 Forum was loosening all the engine bolts, start the bike and lightly rev it a few times ( to get the engine & the frame aligned), then tighten the bolts from (IIRC) the swingarm forward. It made a noticeable but not drastic difference in engine vibration in the 4-5K RPM range.