I am new to this forum and it looks like a great place for info. I was cutting the lawn with my Toro wheelhorse and it just gave a loud bang and shot a huge cloud of blue smoke out of the exhaust. Any ideas of what went wrong? I can still turn it over but each time the plug fires, I get another puff of blue smoke.

It has a 15.5 hp Briggs & Stratten engine model 280777. The oil level was fine and the engine was serviced a year ago for a tune up. The shop that performed the maintenance has since gone out of business.

Not sure if I should tackle this on my own or take it into a shop.

I would start by checking your oil for a gasoline smell, just to make sure no gasoline has leaked into the crankcase due to a carburetor problem. Blue smoke indicates oil burning, tell us did the bang sound like a metal on metal bang or more of a backfire. At this point you could have a blown head gasket or bent pushrod/bent valve.

The sound was from a very large backfire of blue smoke.

Remove your valve cover in the front of the engine and make sure both valves are opening and closing. Did you check for a gasoline smell in your oil?

Yes there is gas in the oil.

Start by doing a compression test, remove the spark plug, put a paper towel on the hole and crank the engine over, if it blows the towel off then you have compression. Or you can use a compression gauge if you have one. If you have compression, next drain out the oil and gas and refill with fresh oil. If your engine has no compression then you most likely have a bent valve/push rod or thrown rod. Both can be caused by diluted oil.
Your gas in the oil was caused by a leaking carburetor, this means the carb must be rebuilt, if you feel uncomfortable rebuilding it yourself then you can have a dealer rebuild it, the carb kit itself runs about $40. If you don't fix the carb your problem will happen again. Your air filter may also now be clogged with oil/gas so you will need to replace that as well as the spark plug.