While the double bearing trick that 3dx came up with is nice, its costly and requires a lot of work. So, I came up with my own method in which I will now share with you all.
Step 1. Remove the engine and shim up the clutch with a few washers. While your at it loosen the starter shaft bearing block along with all engine mount screws. Remove the engine mount bolts also. Be sure that each washer stack is the same height. I used a set of calipers to measure them and used about 5 washers on each side.
Step 2. If you place the clutch bell onto the clutch you can see it sits perfectly flat with zero eccentricity. The start shaft can rock back and fourth in the one-way however it has very limited play when it comes to eccentric movement. Now move the loosened starter bearing block to make sure its completely free, reinstall the clutch bell, and insert a folded piece of office paper between the pinion and the main gear.
Step 3. Now place the back in the heli and be sure it is firmly against the clutch bell so it and the clutch remained perfectly aligned. Clamp the engine to the engine mount with the clutch and bell still seated together and adjust everything as one piece so the gear mesh is correct sort of like the pic below(clamp not shown).
Step 4. Once this is done tighten down the starter bearing block while maintaining alignment. Followed by the engine mount screws for the lower plate, then insert the bolts that fasten the mount to the frame. Mark the left and right sides where the engine and its mount make contact with a sharpy. This is to maintain lateral alignment when you bolt the engine back on.
Step 5. Remove the clamp, then the engine and reattach the clutch correctly. Bolt the engine back in making sure it is in agreement with the marks you previously made. And you know the rest of the story.
These are the steps I followed and my heli has 0 hum and the only vibes come from my crappy rotor blades. Happy flyen.
will wash your heli for a quarter