Valves possibly hitting piston after timing chain replacement?

Has the heads redone the mechanics messed up and forgot to tighten one of the cam sprockets and in result caused it to jump timing. I redid my timing with all new sprockets chains and gears all new now everything lined up like supposed to be. Now when I turn the motor by hand, I get about a half of turn them it stops like something is hitting the piston. How do I get the cam right without having to pull it all back out? It's still down to the chains I haven't put the covers or anything back on I think it's the driver's side cam that's off due to that being the one that was not tightened to spec. How can I fix this?