[Cupcar]

To add my BS here.

To me "deck height" is the difference between the plane of the piston's horizon line (the point of reflection from the piston's side to crown) and the top plane of the cylinder. This is a nice number to have for calculation of deck volume for CR number. I like Steve W's method for measurement of this however one must consider base gasket, if any, crush.

This may NOT be the point of closest interference between piston and head however, for example the piston crown may be close to the combustion chamber above the plane of deck height.

The important thing is that no point of potential interference between the piston and head should be less than .040" = 1 mm is what people say and seems time tested.

One has to look for these interference points when putting odd combinations of head and piston together, particularly with bore increases. For these points I use solder and a head assembly.

Having said that, I have "gotten away" with .035 (Carillo + Mahle forged) at a few points at the combustion chamber edge, but didn't like it.