Valve Timing, 1918 Super Six

Although I can remember this topic being covered before I don't seem to be able to find it in the conversations when I search.

So, I had the marks on the cam and crank sprockets lined up but still had a 'late' opening exhaust valve compared to what measurements are in the book. Adjusted the sprockets one tooth and exhaust now ok but inlet is now one tooth off! I have the cylinder head off and have been using a vernier to determine position of piston crown wrt valve.

Any guidance would be appreciated.

Kind Regards