Depending how the Snap rings are installed is very Important. The open end of the snap ring should be at the bottom of the pin hole. That way when you have the explosion due to firing of the cylinder. It puts pressure pushing down on the piston and Pin retainers and if the open part of the snap ring is at the bottom it applies pressure down on the top of the Snap ring which pushes the sides out to keep it in the ring groove. If it is at the top the downward pressure can push the ends out of the groove and the snap ring pop out. It happens in Big Industrial Diesel Engines and have seen it in gas engines as well. Quite a few engine builders just put the ring in without worrying about orientation of the snap ring.