more valves

sorry to hit you with this being my first post, but i am desperate. I have just rebuilt a 2005 K5-K6 gz125 marauder engine, and the mark on the alt rotor does"t match up to the mark on camshaft. if i set it to what the heynes manual says, the exhaust valve hits the piston at about 20 degs btdc. when putting the cams at the both valves closed position, and the piston at TDC, there is no mark on the rotor. it"s amost like the rotor has moved on the crankshaft, but this is not possible. if i line up the mark that is on the rotor, the piston is near the bottom of its stroke, this is not correct. does anyone know anything about this model. needless to say this engine wont start and im running out of ideas.(ps i haven"t bent any valves). Thanks.

just managed to remove the rotor, and guess what the woodruf key had sheered off allowing the rotor to move on the crankshaft,lining up the two slots,the original timing marks line up. I hope this fixes the non running engine. I will post the results as soon as I get a new key.
I hope this post can be of use to someone who has a similar problem