My car has 145000 and about 3 months ago it started making a knocking sound on start up and last for about 1 or 2 seconds. It started getting louder and then this morning it didn't go away. It is very loud. I replaced the upper timing chain tensioner at around 135000 miles. I took the valve cover off and the chain was tight and the tensioner looked great. I also noticed that when I start it up now, it smokes out of the tail pipe really bad. Is my engine screwed or do I have a valve problem. I depend on this car for my job, please help.