I thought I was a little tired tonite. This explanation is the correct one I believe. I went back to your first post. You had the head rebuilt. So when you put the washer on upside down in relationship to its previous positioning. Naturally you lined up the new mark that was 180 degrees out before installing the head.

This is how you got out that far. Or the shop that rebuilt the head did this for you before giving the head back. Makes sense basically? This is about the only way it could have happened in my opinion. Tired as I am.

The sprocket also does not have two keyways. Your posts and the resultant thread were also a good learning tool for a lot of viewers.