We had a tractor turn upside down on hill while mowing. Oil was pouring out of muffler & burning bad. The engine will start & run well now but still bellows white smoke. What's the damage & what's the repair? Or are we looking at a junk engine now?

Does it make any knocking sounds? How long did it continue running after it overturned?

Make sure your oil level is correct and restart the engine. If it sounds pretty much like it always did you should be OK. It will take awhile running at idle to burn off the oil that got past the rings into the combustion chamber

I agree with BB.

You could spray some carb cleaner in the spark plug hole and with a rag over it turn over the engine.

Replace the plug when it settles or clean well with carb cleaner.