Are you testing each side at a time without blocking off the cylinder that isn't being pressurized? If not, try to block both sides while testing each cylinder and see if you're losing pressure. If your crank is new, you may still have a leak through the center from uneven mating surfaces on the engine case. I had this problem after my rebuild and had to open it back up, touched up the surface slightly with a grinding stone and applied just a touch more 1207b and then the motor held 8psi for 10 minutes solid with either cylinder open while doing the leak down test on the other end.