Hilti TE74 Demolition Tool, no hammer function

Hi,
Does anyone know what sort of pressure can be expected when turning over the air piston by hand for the Hilti TE 74? This drill has no hammer function, The con rod is not broken, there is oil in the gearbox, the piston travels in the bore ok, but I don't know what resistance it should have when turned by hand.
If anyone has any information, it would be great to hear from you, thanks.