Does your engineer not have a tracking and balancing kit? Enstrom's can be made to fly smoothly. There is a host of things that might be causing the vibrations. If the vibration cannot be reduced sufficiently by tracking and balancing then there is probably something worn. Places to check would be the swashplate then the head. There are 12 bearings in the head that don;t last for ever and if one or more of them is not moving smoothly they will need to be replaced to get the vibrations down to an acceptable level.