Bad porpoising after crash repair - any ideas guys?

[Rick Rotorhead]

Broke a blade grip, replaced it (which I have done before, no drama).
Heli now rocks back and forth during hover, builds up quite violently over several seconds until it gets uncontrollable. Blades are a little tight in the grips, I don't know if that could cause it. Any ideas?

[Skiddz]

Tight blade grips *could* cause it as each blade will lead or lag with each revolution of the main rotors. If they're not allowed to swing back into phase, the vibrations could get very nasty.

I assume your blades are balanced and tracked properly??

[zooland1]

And you checked the main shaft and spindle?

[Rick Rotorhead]

Well, no the blades aren't especially tracked or balanced to be honest, but they never have been and I've not had excessive vibration or problems before. The mainshaft is, well, less bent than it has been at other times, so its not a suspect. Ok, so favourite at the moment then is blades too tight in their grips. Its difficult to loosen them off adequately since the retaining bolts are already barely pinching the grips. I think the new blade grips have a narrower opening and the cf blades are a bit too thick to fit in smoothly. Can I sand the cf blades at the root to make them thinner? Or would it be safer to fit a thin washer in to reduce surface contact between grip and blade? Any other ideas welcome.........