Properly adjusted, a solid lifter 6-cylinder engine should emit a rhythmic clicking/metallic tapping sound. There should be no individually louder clicking - it should be a harmonic sound. The sewing machine analogy is a good one... it's simply a smooth mechanical rhythm.

Woody
Your Brother in Bolthood

My 1951 half-ton 'Ol Red

Save the VINTAGE DOOR ART! Please contribute photos.
Door Art Collection