What do you mean half turn? If you used the method of spinning the crank and going through the firing order to tighten the lifters then u should have went 1/4 turn increments. But there are many ways of doing this. The most important thing is.to make sure the valves were closed when you set 0 lash.
Did you soak the lifters at all? And I assume when u checked it they were tight, the valves where closed?
Sorry for the obvious question but many people including myself sometimes can get confused even if we have done it a lot of times.