Motus V4

[Lord Popgun]

Thessler,

Can you expound on coning type vibration?

[thessler3_imp]

Coning vibration is where the two crankshaft ends vibrate in a reverse cone, sort of shaped like two ice-cream cones with the pointy ends in the center of the crank. The two crankpins are 180 degrees in revolution apart from each other but separated by several inches. Think about how a bicycle moves back and forth as you pedal it. All triples and V-4 with 180 degree cranks have it. Some people refer to it as "rocking couple". Most triples have a balance shaft running at engine speed to counter balance the vibration. V-4's are not quite as bad as triples, as their crankshafts are shorter. The coning vibration is sometimes referred to as nutation by automotive engineers. In-line fours do not have it as their outer cylinders go up and down together and 180 degrees opposite the two inner cylinders. You see very few V-4 car engines because the rocking couple is significant in bigger displacements. Although I am not an expert on vibration, I have been studying it ever since my hands fell asleep on my first bike back in 1968.