Step 1: Materials
Engine gasket material
(found online or in auto stores)
Or brown paper bags (this will get the job done
But is inferior to the gasket material)
Liquid ink or industrial sharpie
(Optional) hole punch
Engine (I'm rebuilding a lawnmower engine)
Step 2: Practice
You take the sharpie and draw over the entire edge of the engine quickly, leaving enough ink for it to be visibly wet. You may need to go around the edge 2-6 times in order to get wet ink on it. Immediately after applying the ink flip the engine half onto the paper ink side down and press hard on the top. Remove it and examine your mark. It may take a few times to get this right.
If you're using the ink, dip a Q-tip into the ink and apply it to the edge. This ink will take longer to dry because of the amount but accuracy and speed are still necessary.