the a12a was produce from 79 to 82 the cranks stroke is the same but the a12a crank was stronger the con rods are same length the a12 rod uses a 17mm pin and a12a uses a 19mm pin the a12a block has 76mm bore increasing engine size to 1237cc the block also has the layout as a13 to a15 blocks for mount locations, distributer and oiling of the head.