Jamo

Hi I’m having a nightmare with my g reg xr3i i have put car back together almost finished it but as I tried to turn engine over it cranked really slow I’ve load tested battery and taken starter motor off my brother cabby which works and still same problem when I take plugs out it cranks fine but soon as they go back in it’s slow as if battery is dead I’ve taken head off and pistons are fine stripped head and cam is fine when I turn by hand it seems it too compressed if that makes sense if I don’t know what it could be,anyone has any suggestions it would be much appreciated thanks