When your piston rings or valve guides are worn out, oil is bound to leak to the combustion chamber. It mixes with gasoline/petrol in the chamber and are burnt jointly thereby resulting in the production of the blue emissions. I see it far too when I stage on it and http://valvestemsealreplacement74368.blogprodesign.com/17159378/5-essential-elements-for-blue-tint-smoke-from-exhaust