I guess a warped main gear could cause this but I would say it is not likely. I have replaced 6-7 main gears and every one of them seems to have the same "warped" like characteristic. My performance does not seem to be compromised. Unless it is so bad that you can see the main gear shuttering just before lift off, I would look elsewhere. Look at the collar and the bearings now since you have tried everything else. Make sure that the collar on the main shaft is snug to the top bearing in the frame and in the correct orientation(rounded side up, flange part down to ride on the bearing race). Also when you check the collar, make sure that you pull up on the head to see how much play the main gear at the bottom has. It should be pretty darn snug against the bottom bearing(1/4mm of play maybe). Check that the bearings are not wasted enough to cause a shutter and the small brass spacer is not missing from between the pulley and the bottom bearing. If any of these parts are wrong, you could have an intolerance that would/could cause a vibration.

Hope this helps, there are so many things it could be....Are your control arms on backwards? Elongated part should be toward the inside of the center fly-bar holder.

Hmm?

Z