Did you do the paper gap pinion to spur gear test?
Its trial and error w gear mesh, almost like a black art, lol.
This is how I get it set;
Blue threadlock w a few drops of red to the bottle, medium strength. Install bolts on the engine, secure but not completely tight. Then I roll the chassis on the floor pushing it by hand, going easy and letting the engine sit, like the spur gear will push it and make it right. The engine has to be somewhat secure but not complete.
Then criss cross, easy, roll, cc, roll, and tighten all the way down. A few silly drops of thin light oil, 25w shock oil, 3in1. Just a bit, roll and see if is still binding.
Factors to check;
Clutchbell bent
Clutchbell bolt bent
Clutch gear out of round warped
Spur gear warped, rare
Dirt or oil underneath engine or where the spacers go
Barely stripped bolts, fatigued, swap as necessary
Low quality clutch gear, buy brand only
You did not specify what brand the gear is. I will say, I installed a Rovan 19t on my X2.and lasted half a tank. Now I am running Losi 19T and spacers, no more issues.
Once all nice and tight, take it cor a spin and bring w you the allen wrench, bring it back, tighten, another spin, jump it, check, push roll it see how it sounds.
If you still have problems redo everything, and check for bent parts, loose stripped bolts on center diff housing, chassis flex.
Two things I always check when driving the damn monster, carb is not loose and proper mesh.
