I have been chsing down a wicked vibration in my 600n the past few days, it was most noticable on spoolup or spooldown, but sometimes if I made a hard negative collective descent and pulled it to a hard stopping hover the whole helicopter would shake. The skids and flexible tailpipe deflector would become a blur.
Anyway, last night I balanced the fan, checked the runout on the main shaft, tail shaft, and clutch, balanced the tail blades and paddles, and made sure that the flybar was centered with the weights spaced out equally.
So today after work I decided to run it up in the driveway without blades, basically into a fast idel so not to overspeed the engine and lo and behold the damn thing still had a vibration. About this time I noticed that the head button was moving around a bit. So next withthe head at a good idel I bent down to look at the head level with the blade holders and wouldn't you know it the blades holders were out of track. This is without and blades on and I had just put in a brand new feathering spindle.
I shut it down and took in in the garage to swap out the head block as I had another whole head from when I put a 600 head on my Raptor. After swapping everything over I ran it again and vibration gone, blade holders were perfectly in line.
I have stuffed it a few times pretty good, but I would have NEVER imagined that I could have tweaked the head block like that! I mean, it is a pretty good chunk of metal but I guess that anything is possible. I am really looking forward to trying it out now that everything is nice and balanced, but alas it looks like it is going to snow here in Dallas tomorrow (yes Dallas) and just generably be colder then us Southerners like, so I guess that it will have to wait for a few days.
Have any of you managed to tweak a head block? It must have taken one hell of a wallop....