[Richard]

The exhaust manifold bolts did not seize on me as I feared, so getting the head off was pretty straight forward. Remove the intake and exhaust manifold, get the injector lines removed, take off the valve train, and let the impact wrench take the head bolts out. 

It was pretty evident upon removing the head that cylinder 1 was not burning cleanly at all. You can see a pic of the crud on the valves. Plus the exhaust port was all gunked up with a 1/4 inch of carbon.
   

When I pulled the valves out. Here are pictures of the exhaust valve and seat in cylinder 1.
       

It’s pretty evident, that those two mating surfaces are not going to seal. The other exhaust valves were a little pitted but nothing like cylinder 1. There are lots of opinions on the interweb about what causes the valves to pit like that, but the leading contender is carbon deposits that build up on the sealing surfaces and get hammered into the seal each time the valve closes. I started by lapping the valves and seats. It worked just fine to restore the valve and seat on the intakes but I would have been lapping for a week to fix the exhaust valves. So I did a very light grind to remove the pits, and followed up with lapping. I was unsure if this would work or if I would need new exhaust valves and seats. Luckily, I didn’t have to remove too much metal, and I was right on the edge of Yanmar specification for seat width and valve recession. Here are a couple of pics of the valve and seat from above after some TLC.