what center pulse rudder you have set in SERVOS - TYPE ?
for servo rudder 3515t is exact pulse center 760us

Hello Franz, the center is set to 760, see attached screenshot.
In my EdgeTX remote, the output at 1500, but i think this is not relevant as I use FrSky Fport....

I also attached my complete Spirit-4ds-file.

Regards, Chris

I only have one idea left
for that size of helicopter those rpm are few
try 2700 rpm
for me you have few rpm rotor
my 580 use 1900-2000 rpm and the helicopter the smaller it is and the more RPM you have to use.
start at 2300 rpm and increases the rpm until you see that it flies well
for me a helicopter size same as yours It must fly at almost 3000 rpm
I don't know omp but I can tell the turns of my helicopters
my sab goblin raw 580 1900/2000 rpm
my trex 600l dominator 2300rpm
trex 450 3000rpm
trex 600cf 2100rpm

I think everything is ok you didn't find the RPM exact for your helicopter
Maybe the problem it happens only in a certain rpm range can disappear exceeding those rpm
my old helicopter trex 450 it's the size closer to yours and I used 3000rpm
PS
the manual omp m4 has RPM min 1400 and RPM max 3000
Find the right RPM for you

No, the rpm are correct an quite perfect for this heli. Attention: this ist the M4max, not M4. The recommended rpm were posted on page 2, and I am not Tareq
And as I stated before: the problem grows with higher rpm.
I will commence tuning the governor, maybe the path to success lies there

Let me know how to solve the problem.
The tail he was going crazy for an esc that wasn't working well.
I'm curious to know
Ps
Thrust bearings they are mounted exactly?
the part of the spheres towards the outside.
The part with the edge towards the t hub

I understand the problem.
Online i found many posts of problems of the tail of your helicopter model.
The problem is the servo tail, you just have to try another servo tail (a different brand) and you'll see that it will go well.