[ivymike1031]

My reasoning was anything but rigorous - I had observed that the vibrations I was interested in were excited very rapidly (showing up during the opening flank), and decayed pretty quickly after valve closure. Because of this, I figured that I'd just focus on the lift events themselves, without the period of decay, as though the valve was getting "bopped" repeatedly. It may have been a wrong-headed approach; that wouldn't surprise me at all. I wasn't entirely sure what I wanted to look for when I did it, and I didn't learn anything useful by doing it.

If I emailed you a "typical" lift profile, velocity profile, and acceleration profile, would you be interested in manipulating that data to see what you can learn about it? I'd certainly appreciate some input, especially since it sounds like you've got more experience with frequency-domain analyses than I have.