jay it sounds like the crank seal on the right of the bike, When this seal passes the engine oil gets into the crankase as so gets burned producing the thick smoke, its not a full strip...not even an engine out job but you will need a clutch holding tool to hold the engine still so you can undo the nut on the primary gear altrenatively you will need to remove the cylinder piston and head and place a rod (1/2 inch drive extension bar) through the small end onto wooden blocks so the small end is approx 1/2 stroke
aside from this is it possible you forgot to fit the 'O' ring under the spacer behind the primary gear when you worked on the bike last?