> Why do you think that those frequencies are far above 50 Hz?

50 Hz = 3000 rpm, but some of the parts like the valves only
move during a portion of a revolution, and have higher frequencies.
Camshafts are 2:1, I think, so if a lobe is about 30 degrees then
the upper frequency might be around (50*2*24)=2400 Hz sound
at 3000 rpm, or 160 Hz at a 200 rpm idle.

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