I tried to start our riding lawn mower and the engine would not turn over had only been a week since the last run. I opened the hood and manual turned the top of the fan assembly (3/4 of a turn) and tried the key again and the engine started. Backed out of the shed and started to heading forward placing the blades in gear. When the blades were in gear white smoke filled the backyard (looked like I was spraying for mosquites). I pulled the head off and found a couple of oz of oil in the cylinder. The cylinder wall looked smooth and clean the. (this is an 8 year old mower) So why would I have had to turn the fly wheel to get the motor started, why would it have smoked like it did? Why would there be oil in the cylinder?

Could be valve clearance is off.
But did you check your oil level ? Sounds like you cold have gas in you oil , this will make it smoke and hard to turn past compression stroke.
LUCK