Hi John,
Thanks for this quick input.

Guess what: I didn't even think of the cam! And it sounds like you got the right diagnosis, because the noise fades and eventually disappears totally as the RPM go up.

The mileage of the engine is unknown, but it still pushes hard although the rings must have seen better days (oil comes out from the oil filling cap quite a lot, no PVC installed though).

This being said, have you experienced long service period with worn out timing gears or is this a "fix it or it'll die soon" situation?

Also, do you know where to source new thrust plates in europe?

Thanks for your help,
Séb