Hi Jeff/Colin.
Thank you for your replies. The handbook is the same as i have for the helicopter.
Colin you have just put your finger on the problem. I have had a close look at the assembly detail in the manual and see that the part identified as 030 has not been installed. The part does not have the grub screw provision and therefore the problem has existed from the original purchase of the helicopter. I spoke to my son today who owns the helicopter who told me he never actually managed to fly it. Now we know why.
I have ordered two collars and see what happens when they arrive.
Thanks again for your help.
Stay safe.