other smoking could be caused by *worn piston rings as you said (checking compression would be a good idea) *pcv valve blocked *valve stem seals gone (try taking the car for a drive, pick up some speed and drop it down a gear and let it slow down with engine braking, if it smokes more when you do this then valve stem seals will be bad.) *head gasket (check for mayo looking gunge round oil filler cap) quite a few possiblities to be honest and lots of ways of testing. search on here theres loads.