Bought a new house on about a half acre lot and got a new John Deere D 110. I mistakenly overfilled the engine with my fist oil change by about 1/2 a quart. After mowing for about 20-30 minutes it back fired a couple times and billowed white smoke. I put the mower up and tried again the next day. After about 20 minutes it back fired and billowed white smoke again. I now realize that I had overfilled the oil. I've drained some and all seems to be fine now. Do you think I did permanent damage running it about an hour overfilled?