RC:

As Don, & I, and others have suggested, the most critical parts are the main shaft, Feathering shaft, all of the ball's tightness in their holders, and, of course, the links themselves. As Don suggested--Start from scratch---Re-Measure everything --Realistically do a total setup. Even use new blades, though I doubt that's the problem. Don't just look at the Main & feathering shafts--REPLACE them--Without precise measuring tools you'll never find a bent shaft. Even the "mildest" crash, where the blade hits something, 90+ % of the time the main & feathering shafts will be bent. I always replace both!!! AND--I've had more than one occasion where a brand new main shaft out of the package is bent. Amongst my large supply of spare parts are at least 15--20 main shafts and featheing shafts.

And do check out the whole head geometry--Be sure the damper grommets on each side are intact and the head is very firmly screwed together.

Don't start worrying about motors, pinion, etc---Get the set up correct & you'll be OK.

And as Don said, bouncing all over the forums will lose the continuity necessary to help you.

Good Luck

Lloyd