First, place the correct size wrist pin boss of the piston to use as a tool from each side. Then place the ring to be squared in the cylinder. Be sure not to push the ring down too low. Now, with the piston upside down, push the ring with the top of the piston until the wrist pin stops at the block. To verify ring is squared in the cylinder check with a simple depth gauge. I have found this method to be simple, quick and accurate.
Next, verify ring seal. While keeping the feeler gauge snug in the ring gap take a flexible light with the flex part bent in a u-shape and shine the light right under the piston ring to cylinder area. Move around the whole cylinder and look at your gap. Needless to say no light should appear between the ring and cylinder, or the gap. If it shows light through try a ring from a cylinder that does not leak. This will determine if the leaking light is coming from the ring or the cylinder wall.
Animal Jim Racing and Animal Engines