i replaced head gaskets in 98 caddy 32 valve northstar engine. i marked both cams before removing chain then put cams back in exact same place. put chain on now engine valves rattle on left side. i pulled front covers off and both valve covers then lined up timing marks on crank with all 4 cams timing marks at 90 degrees and still same rattle like engine is not timed. what am i doing wrong?