Hurth HBW100-2R Gearbox

[AprilLady]

I cannot select any gear with the engine running but with no engine, I can select the gears. It is not linkage as I have disconnected it.

 

[Boater Sam]

You say cannot select gears, do you mean that the lever on the gearbox will not move when the engine is running?
Or do you mean that there is no drive to the prop?