compression could be down due to the valves on the head but ive been reading up and if there is a variation of 1 bar between any two cylinders is a indication of a fault.... so new head my be a good idear but may be in same situation!! anyway get the new head fitted and if it still happening time for a bottom end rebuild, just hope that the cylinders are not scratched... other wise you will need a rebore with bigger pistions!!!