Mass of the engine+frame is approximately 500kg. The mount will be U shaped, with the supports level with it's CG - approximately at flywheel level. It's operating speed is 650RPM. There will mainly be 5Hz power/torque pulses, but there will be a 10Hz component due to imbalance in flywheels from the factory, although this will be reduced as much as possible. There may be opportunity to increase the mass of the system, possibly double it.

I'm looking at air-cushion isolators from firestone, which have a natural frequency of about 80Hz. These - according to their charts - should give abut a 95% isolation. Googling around shows many heated debates about internal engine stresses and possible fatigue issues if it's mounted on flexible mounts, although I have trouble understanding why.

Anyone have any ideas or suggestions?