They were actually held in suspension by wires. Many times you can find core wire inside an old block if it has not been cleaned out well during previous overhauls. The wires become part of the block during the pour but they sometimes melt out of position or were not placed in the mold box well during assembly of the mold. THis can shift the placement of the cylinders enough to make one side very thin and the other very thick. The only way to non-destructively test it without X-ray or gama-ray pictures. is with ultrasonic equipment.