Originally Posted by high voltage
Unless you are hand swinging I wouldbnt be rotating the prop, other than a few degress to eg attach the pull bar to the nose wheel. Too many people have no respect or understand how to handle the prop, therefore I always tell them to leave it alone! I can't see it ever firing by rotating it counter-clockwise due to the timing set-up but you could easily destroy the suction pump.
You should turn the prop on some aircraft particularly those with upside down cylinders (radials, some in-line 4s and 6s) to clear any oil and make sure you don't have any hydraulically locked cylinders.
Best to teach them how to do it properly rather than tell them to leave it alone.