Hi all, I acquired a used tractor from a friend (Briggs motor: 445677). It was running well for a few months and then started blowing black smoke. After reading various threads about Intek engines blowing head gaskets, I decided to replace the head gasket. When I took the heads off however, I did not notice signs of deterioration in the head gasket. Nevertheless, I replaced the head gasket as I had to scrape off bits anyway. I cleaned up a decent amount of carbon buildup from the top of the piston and I used fine drywall screen and seafoam to "sand" the bits of old gasket from all surfaces. Unfortunately, during the process of reinstallation, I over-torqued the head bolts (wrong setting on torque wrench). I, ultimately, torqued them to the correct torque (but I was sure I had at least compressed the gasket or worse, warped the heads). Anyway, I put everything back together and the engine still smoked. It also appear to have oil visibly leaking onto or from where the exhaust pipe connected to the head. So, I suspected a warped head (either from my over-torquing or from previous overheating - the engine was quite dirty when I got it). I ordered two new head kits (came complete with head, intake and exhaust gaskets). This time when I replaced the heads, I filed down the exhaust pipe connection as it had quite a bit of old gasket material stuck to it. I also made sure all metal contact surfaces were cleaned again and I set the valve gap to .004. With new heads and new gaskets, I was SURE the smoking problem would be solved! Well...still smoking from, again, what appears to be around the exhaust port. This time, I don't see any visible moisture/oil from that area. I should add, that when I run the machine, I don't have the air filter hooked up (if that matters). I should add, the engine now has an occasional stumble and it will backfire when moving from full throttle to idle. And, the engine smokes more at idle. I've been reading threads about the issue, but thought I'd post to see if anyone has suggestions about any TESTS I can do to narrow down the problem. I've read the following: 1. take the exhaust pipe off and run the engine to see if oil drips out 2. take the valve cover off and shine a light into the chamber to see if oil is leaking into the chamber Ideas of the possible problems: 1. is the engine block surface warped from over torquing the head bolts? (except the same symptoms are occurring before and after the head replacement). 2. bad piston rings? 3. ? Thanks in advance for any help.