I've been looking at the fuel in the tank to see any engine vibes as I guess they would be quite high frequency and I've read about 'foaming' indicating an engine balance issue but this one seems to be in the tail for sure.

I've got to replace the feathering bearings before I fly it again so might as well check the rotor output shaft while I've got the spanners out.

I'l let you know when I've flown it again.

cheers

bit of an update...

tail rotor output shaft was straight but on the blade end it looked like the diameter was too small when it was ground to size so there was like an angled step where the hub located so that is being replaced along with a few other things.

replacement parts have arrived and are as follows :

Tail rotor output shaft
tail main pulley and idler pulley
main idler pullies
new belt
new starter shaft
new main bearings
new clutch / pinion / starter shft bearings
and some new tail and main blades.

One of the boom stays had been repaired but was lose so I have made an effective repair for now but I will replace them if they give me any trouble

some of the replacements were preventative but some were necessary to replace worn out items.

I will also be replacing the carbon tail control rod with a wire type with guides as the carbon one was to big and was rubbing on the tail case.

I also checked he fan / hub run out on the engine and it was within a few thou' so that should be OK. The engine is bearly run is so my vibes must be mechanical somewhere else. The starter shaft looked quite worn and the new one sits much better in the clutch and some of the bearings were not as tight as they should have been. They didn't feel bad, just worn as you'd expect from a older heli.

I split the main frame last night to fit the new bearings so should be up and running again the the next couple of days.

I'll let you know how I get on.

Cheers

Sounds a very likely culprit mate.
The hub being even slightly off centre would obviously give you a whole world of pain.

hope so, although I will not find out until the w/e now as the new shaft I got was bent...... so now waiting for another replacement.

also a couple of other issues to resolve...

the wire tail control rod is just a little too long so I need to cut about an inch off the end of it and re-thread it. Hopefully not to difficult a task..

and I broke my 1.5mm hex driver last night so I can't do up the main shaft collar or the grub screw that holds the pin in the tail output shaft.....

oh well..... only a day or two more..