I am building an Atkinson Differential engine and I am having a problem getting enough compression to run. I have made several pistons and rings. I have made rings using the Trimble method and been very careful to use the method and hold tolerances. When the pistons move to the right to the firing position I have leakage around the skirt of the LH piston and only low compression. Once it has reached TDC and the piston starts to move to the right it creates a very good vacuum and will hold this for several seconds. I cannot understand why I am getting so much leakage on the compression stroke and then immediately get a good seal as soon as the piston direction changes. As I said I have made at least four different pistons and at least 8 sets of rings and nothing seems to change.