Greetings All, Assistance needed from the engine guru's out there. To cut a rather long story short I have just completed the rebuild post head work. Only changes apart from the Skimming, porting, polishing and valve lapping of the head were fitting of a thicker 1.2mm copper gasket, a new cylinder stud and a change of oil to 10w 60 (mobil 1 older engine performance oil) Engine started on the button, oil pressure as normal, but a loud very alarming metallic rattle or clacking was evident when the revs were raised above 1200 rpm and when the engine was revved it rattled on run down. I have now stripped the engine down and can report that there is now light vertical scoring in the bore sides and on the piston sides (opposite side to gudgeon pin not the forward and rear faces)see pic's. The rings are all intact and clean. Big and little ends are firm and there was only slight contamination of the oil with three small 3 x 1 mm pieces of material on the sump mag plug. I'm so glad I didn't drive the car as it may well have gone bang! So, question time what the hell is going on here???? This noise was not evident prior to rebuild and oil change??? What has caused the markings on the internals - possibly Piston slap but why???? HELP!!!!