Also found a site that said take rpm/60=Hertz, don't need a sirometer. 2700rpm is about the worst spot. 45hz. Same site said for internal engine stuff take second order so 90hz. What I can't find is something that says what materials or component matches that frequency.
Once you figure out your Hz, how do you figure out if it's a 1st or 2nd order harmonic? And then what is a guide for where to look at in/on the engine? I'm trying to read up, but it's almost over my head
