Check the exhaust valve guide clearance- - - -lots of oil can go down the exhaust pipe without ever being noticed as fouled spark plugs or smoke. If it doesn't get into the combustion chamber and get burned, the characteristic blue smoke doesn't always become apparent.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!