(I do not have an engine to show in this Instructable, and have decided to use a holesaw to represent an engine cylinder. The bottom of the holesaw represents the top of the piston.)
Step 1: Measure the cyclinder's diameter
Step 2: Round the ends for better fit
Step 3: Drill-end-to-end
I made guide lines in pencil and drilled by hand. Because bits this size are short I had to drill from each end to make a hole that runs the full length of the block. Happily, my holes met in the center. Even if they do not meet, this device will still work, but the holes should at least be close to meeting.