Why you should be cautious about harmonic dampers with moving fluids or weights.
Fluid Dampers and harmonic balancers with balls, springs, or inertia rings with rubber o-rings are very expensive (more than the cost of balancing many engines). And they cannot be accurately balanced. Centrifugal force will move the inertia weight (ring or fluid) off “center” no matter the RPM. As the RPM increases, so does the centrifugal force, so your engine is almost, but never quite, balanced. Centrifugal force will not allow the inertia weight to center no matter what the RPM. The heavy fluid, or moving weight, is always playing “catch-up” with the actual rotating weight of the engine.
However, fluid dampers do help dampen the torsional vibration induced by internal combustion engines, so while they are very expensive, they do have a function. Fluid dampers can be added to a neutral balanced rotating assembly, but they are not a substitute for a properly balanced engine.
We know of one customer who even cracked the front main cap on a Chev V-8, and another cracked the nose of the crankshaft due to extreme vibration induced by running an expensive fluid damper on a high RPM performance engine that had not been balanced.