Ok, so what exactly does the readings tell you?  Ring issues, crank sealing issues?

Nice DIY tester Mitch!

On engines that have power valves, it usually tells you that you need to figure out a way to keep the power valve from leaking air into the crankcase so that you get an accurate pressure and or vacuum test.


Once you solve the power valve sealing issue, a pressure test will help indicate leaking gaskets, cracks in the cases or cylinder and if the pressure lips on the crank seals are leaking.  IT WILL NOT REVEAL IF THE CRANK SEAL SUCTION LIP IS LEAKING.  Crank seals have two lips.  One lip holds pressure and the other suction.  The suction lip is the most important lip and the lip that is most apt to leak causing a lean condition at partial throttle.  A vacuum test is also necessary to accurately test for leaking crank seals.