If you put too much oil in the engine when its rotated it can hydraulic lock and with enough force you could bend something, like the rod. I remove the glow plug and then put lots in the bottom end of the engine. I then rotate it by hand and then rotate it with the electric starter. Watch the oil coming out the glow plug hole!! I usually turn the airplane so the engine is upside down so the oil does not shoot straight up. I then repeat the process at least twice. I then reinstall the glow plug.

If you take the engine apart right after this, you will notice the insides are coated very well and there is not much excess oil, to get in the way the next time you start it up.

I have used in the past air tool oil and now I am using a 50/50 mix of air tool oil and ATF. Seems to work well and smokes less on startup.