I have a 1991 560 sel. It is having a knocking in the upper end, I assume valve knock. I thought maybe a stuck lifter but it doesn't appear that this engine has lifters per se. Anyway, from what I read the valves are adjustable and I'm wondering what exactly I should be looking for when pulling the valve cover. I'm getting some smoke when I start the motor and until I put some Sea Foam in the crank case, was getting some smoke upon acceleration. After the Sea foam there was decreased knocking and smoke but it's still there and I suspect valve setting and possibly valve seals. Does this head require removing in order to replace the seals? And, should an adjustment to which ever valve (how do I determine which valve(s))quiet an otherwise strong motor? Thanks