i have a problem with the timing gears. when all the gear marks line up should the #1 piston be at TDC or at the ADV. mark? cause last time i put it together i lined up the marks but the piston didn't line up and when i got it together and started it up, it ran but but it backfired through the intake and the exaust. it didn't do this before i took it apart. the reason i did take it apart was to change out the oil lines cause they had cracked. i now have the marks lined up again and i did rotate the engine twice to make sure the marks lined up again and they did but the piston isn't at TDC. does anyone have any info on how to fix my problem?