Not sure if it's a motor or belt problem?

I have had a few minor tail boom strikes and a minor crash lately.
There is nothing serious on the boom itself.
Before the crash the rotor head was stiff to turn by hand and made a squeaking noise.
Yesterday I changed the main shaft & feathering shaft. I made sure that nothing was over tightened.
The problem is still there, but seam’s worse now. With the battery disconnected & the Tx turned off, I tried to rotate the rotor head by hand it turn’s only if I really force it, and it really squeak’s. I noticed that when I turn it by hand the main gear does not turn for a few rotations but the tail blades still move, then the pressure releases a bit and the main gear starts to move again! But still stiff.
With the battery & Tx on, when I apply the throttle the motor jerks’ forward’s & backwards like it is really struggling. I thinks it made a noise two?. For a few sec’s the blades wont move, then all of a sudden after a little more throttle the main blades spin up like the brakes have been released dangerously fast.
I don’t think it is the motor that is the problem, as it is really hard to move the rotor head even by hand with the heli turned off.
Any suggestion’s are greatly appreciated.
Thanks’
Marc
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Not sure about what heli you have,but it sounds like damage to the oneway bearing
on the main gear. You need to investigate this because I doubt it will fix itself.

Back off the motor first and then try turning, if it still does it then we know its not the motor.
Then loosen the belt and pull it off of the pully. Then turn the rotor again and if it still does
it, then we know for sure its in the main system. Main bearings or oneway bearing.

Thank You. I am going to try these suggestions.
It is a CP V2.