In all honesty, hard mounting 4 strokes is much better then trying to use vibration dampeners. Usually rubber type spacers have give to them that actually excells the vibration. I've always hardmounted 4 strokes to whatever plane they've been one...whether on a metal motor mount or not....no spongy type rubber material is used to isolate the motor. I tried it a couple times and it actually shook the plane half apart.