Like Montague said, but I'll add a bit more. SOME new ABC engines are difficult to turn through top dead center WITH a prop.

I've seen one or two that I thought were hydro-locked, but weren't. I was nearly afraid to force it through compression.

Tom,
I'm guessing that you meant 360 degrees, or one full rotation. You should be able to turn it 180 degrees each way if you're centered on the stroke.
Dennis-