My briggs and stratton 14.5 hp smokeing?

I just bought a used Yard Machine with a 14.5 OHV rideing mower. I cut the yard and before I was finished it was "bellowing out white smoke (smells like oil). I checked the oil leave...good, cleaned the air filter, added freash fuel and still the smoke is comeing out....more when under a load. I'm thinking bad ring's? I've got no oil leaks anywhere on the mower, so Im thinking I need to replace the rings? Thank you for the help in advance.......Will