I have a Snapper SR1433. It is about 10 years old. I was mowing this past Saturday when, suddenly, the blade stopped turning, the engine sounded like it was under a heavy load and smoke started pouring from underneath my seat. I got it back to the shed and stood it on end to check it out. There was nothing binding the blade as I suspected but I could barely turn the blade by hand. What is causing this and what do I need to do fix it? Thanks for your help.