I usually break engines in on the airplane. Get it adjusted enough so that it's reliable and then go fly. It's not like a glow engine and will tolerate being out of tune quite a bit before actually quitting on you. There is no mention of what brand of prop you are using. Some prop designs have not been updated to accomidate multi bolt hubs. Vibration harmonics is a complicated topic and the combination of prop, mount and RPM may be putting it into a destructive harmonic. The other thing is the prop bolts on a wood prop should be tightened to about 45-50 in lbs and checked frequently. Over tightening them will cause them to fail. Some manufacturers also supply grade 12 bolts and in some cases they can be too brittle. I always swap out bolts to stainless grade 8.