After a major crash, I changed Esky Belt CP's main frame and few servos. Its boom was bent to I make it straight. Yesterday I completed all the assembely.

This heli is not able to hold its tail now ..... Its rudder survo is perfectly working but I am not able to control its tail movement with extreme left or right commands to the controller.  It's rotating on its axis.... like a dog running to catch his tail..

Its behaving as if there is no tail rotor.

Belt tension is fine,
servo is fine
gyro is fine

where is the problem

Try reversing the gyro compensation direction ON THE GYRO. 

Note that this is NOT the same as reversing the rudder channel IN THE RADIO.

Hi Arvind,

You need to check the following things:-

1. make sure that the tail servo and tail slider is moving in the right direction (check in manual )

2.  As you reinstalled the boom, then also check that the belt is fixed properly(turned only half step and no crimps inside the boom) and also that is making the tail rotor move in the right direction (clock wise if seen from left side of the heli , Nose on your left)

3. As you installed a new Servo, I would agree with Anwar to check direction (NOR or REV ) the small blue switch on the Gyro (see manual)

Thanks
Hellyflyer

If all of the above points suggested are intact on ur heli(belt tension, gyro direction and servo), check if u stripped the front gear set on which the tail belt loops around. If it has stripped teeth, the torque counteraction between the main and tail rotors may not be effective, making the heli do circles on the ground.

That being said, I strongly share anwar's suspicion that it's a reversed gyro that is causing the trouble. Getting it to NOR should fix it

Wow, its fixed by reversing gyro

thank yo all