You can absolutely have one 180 degrees out all marks lined up and will not start, just backfires, proof right here, watch mark on flywheel (08 YZ450F subject) turn cams to 10 and 2 and marks line up TDC also through plug hole, now turn and watch flywheel mark line up and look at cams they are down and valves are open. I dont care what none of you so called experts say Ive had one 180 out and pop only trying to start, remove cams rotate to flywheel mark reinstall cams and boom first kick, enough said. And by the way Ive been doing this 25 years and it just happened to me for the first time, thank you and goodnight.... If you were 180 off the piston would be a BDC and if Im not mistaken the piston would hit the exhaust valves. Bring piston to TDC (dial indicator or align stator mark with cover) and time cams. Thats it. Its not that difficult.