EC120 T&B
Not sure if this helps but I will give it a shot. We operate 3 EC120's our high time ship is coming up on 4,000 hours and #2 is close to 3,500. We almost never do a track and balance. If you are trying to get rid of a vibration that you cannot seem to fix with T&B, adjust the RRPM. We have found that the hammers are tuned to a specific RRPM. As little as a 2 RRPM difference in this equation makes a HUGE difference. Ours are smoothest at 409-410 RRPM. It does not seem that this would make a big difference but it does. If all else fails try this and see if it works. Hope this will will smooth things out for you.