[SAJ]

Frank. The timing cover spring was replaced with an adjustable threaded stop early on in the saga. No effect on the gear clacking noise. A polythene bolt threaded into the timing pin hole against the fibre gear immediately stopped the noise as an experiment to prove it was timing gear noise.
The post is about the beneficial result of a simple torsional damper on crankshaft harmonics really. As T Bird points out in a PM, putting in an aluminium gear with no backlash in not a good idea. But I ordered new crank and cam gears and when they arrived, that is what I got for backlash when fitted. They were free and not binding and I covered them with moly paste to ease the run in.
I had to get the car going for an event, so fitted them and I guess they wore in badly to give the noises and I got what I deserved. I will take the front cover off one day and see what backlash there now is.