To truly find out the compression of an engine (and each cylinder) you need to first figure out how many cc's of volume there is in each haed. To do that I cut a piece of thick, rigid plexiglass then drilled a hole in it.
The valves must be closed, and the spark plugs must be in place to keep the liquid in.
The plastic goes on the head with petroleum jelly or white grease around the rim to seal it.
Using a graduated pipette, fill the head through the hole until there are no air bubbles.
#1 - #3 were all about 59 cc. But #4 was 62.2 (I did the measurement twice just to make sure). So it's possible that there might be a different thickness barrel shim that goes on that cylinder. There is a formula for determining compression, but I need to know my deck height, and I won't know that until I install the pistons.
==============
Running total of hours spent: 1.5 2.5 3.5 2.0 2.5 2.0 1.5 2.5 (18 hrs total)
Water w/ food coloring, and a pipette
Colored water fills the head through the small hole.
When all the air bubbles are gone the head is filled.