RE: fpe 5.8 with the shakes...
Twisting vibration is called torsional vibration by the engineers, but it means the same thing. If I said torsional vibration, two thirds of the folks reading this wouldn't know what I was talking about. Every power pulse of the piston tries to twist the crank one way, every time the piston compresses the mixture tries to twist the crank the other way. The crankshaft has a natural resonance frequency (where it sings like a guitar string). Bad things happen if the power pulses are in tune with the resonance frequency of the crank. The harmonic balancer dampens out these vibrations. Like a guitar string, you can change the resonance frequency of the crank by changing the diameter (stiffness). But, this has nothing to do with the type of engine mount. Crankshaft torsional vibrations are not damped out by travelling through the engine mount. It's the torsional vibrations that will damage the crank and the bearings.