[Dave at Pelican Parts]

Cut a piece of plexiglass to fit in the register where the cylinder fits. Cut a hole in it. Get yourself a "graduated cylinder" from a science-type supply house. Fill the cylinder with a known amount of water (that's what the "graduations" on the cylinder are for), pour carefully into the hole in the plexi. Carefully work the bubbles out from under the plexi, and stop when the water is touching all of the plexi. Check how much water is left in the cylinder. The difference is how much volume in the chamber.

Repeat several times, average the numbers to help minimize measurement error. A difference of 1CC is actually a fair bit in this context.

--DD