Just for fun, a sample (may not exist) crankshaft and its harmonic orders. Natural frequency: 250 Hz. The orders are located at: RPM = Hz × 60 ÷ N, where N is the order number.
Ranked by severity (magnitude of damage from sustained use), worst on top:
#3 5,000 RPM
#2-1/2 (yes, it's there) 6,000 RPM
#2 7,500 RPM
#6 2,500 RPM
#9 1,667 RPM (pretty weak)
#12 1,250 RPM (almost harmless)
#1 15,000 RPM (pretty strong, but out of reach)
#4, 5, 7, 8, 10, 11 = harmless in an L6
A V8, L4 etc. will have the same orders (if the Hz matches) but which ones are important will be pretty different.
